Typical Operating Circuit
N
M1
MAX4271
MAX4272
VOUT
CBOARD
CTIM
CSPD
CTIM
ON
ON
GND
STAT
VCC
RSENSE
STAT
REMOVABLE CARD
2.7V TO 13.2V
BACKPLANE
IN SENSE GATE
GND
General Description
The MAX4271/MAX4272/MAX4273 comprise a com-
plete family of integrated 3V to 12V hot-swap con-
trollers. They allow the safe insertion and removal of
circuit cards into live backplanes.
The discharged filter capacitors of the circuit card pro-
vide a low impedance to the live backplane. High in-
rush currents from the backplane to the circuit card can
burn up connectors and components, or momentarily
collapse the backplane power supply leading to a sys-
tem reset. This family of hot-swap controllers prevents
such problems by regulating the current to a preset
limit when the board is plugged in, allowing the system
to stabilize safely. After the startup cycle is completed,
two on-chip comparators provide DualSpeed/BiLevel™
protection against short circuits, load glitches, and
overcurrent conditions. In the event of a fault condition,
the load is disconnected. Fault recovery is handled by
unlatching (MAX4271), autoretry (MAX4272), or pro-
grammed (MAX4273) methods.
The MAX4271 family includes many integrated features
that reduce component count and design time. An on-
board charge pump provides the gate drive for a low-
cost, external n-FET. Integrated features like startup
current regulation and current glitch protection eliminate
external timing resistors and capacitors. Also featured
are an open-drain status output to indicate a fault condi-
tion, and an adjustable overcurrent response time.
The MAX4271 (latched fault protection) and MAX4272
(autoretry fault protection) come in 8-pin SO packages.
The MAX4273 (full function) comes in the space-saving
16-pin QSOP package and 16-pin SO package. All
parts are specified across the extended temperature
range, and have an absolute maximum rating of 15V to
provide extra protection against inductive kickback dur-
ing board removal.
Features
♦Provide Safe Hot Swap for +3V to +12V Power
Supplies with Few External Components
♦Unique Current Regulation Architecture
Minimizes n-FET Linear Mode Duration
♦Autoretry Feature (MAX4272/MAX4273)
♦DualSpeed/BiLevel Current Limit Protects Against
Current Glitches and Short Circuits
♦Power-On RESET (MAX4273)
♦15V Absolute Maximum Rating Protects Against
Inductive Kickbacks During Board Removal
♦Internal Charge Pump Generates Gate Drive for
External n-MOSFET
♦Status Output Pin Indicates Fault/Safe Condition
♦Space-Saving 8-Pin SO, 16-Pin QSOP Packages
________________________Applications
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
________________________________________________________________ Maxim Integrated Products 1
19-1694; Rev 2; 12/07
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
EVALUATION KIT
AVAILABLE
DualSpeed/BiLevel is a trademark of Maxim Integrated
Products.
Pin Configurations appear at end of data sheet.
Base Stations
RAID
Remote-Access Servers
Network Routers and
Switches
ISDN
Ordering Information
PART
TEMP RANGE
PIN-
PACKAGE
PKG
CODE
MAX4271ESA
-40°C to +85°C
8 SO
S8-1
MAX4272ESA
-40°C to +85°C
8 SO
S8-1
MAX4273EEE
-40°C to +85°C
16 QSOP
E16-1
MAX4273ESE
-40°C to +85°C
16 SO
E16-1
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN = +2.7V to +13.2V, TA= -40°C to +85°C, unless otherwise noted. Typical values are at VIN = +5V and TA= +25°C.) (Note 3)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Note 1: GATE can be pulled below LLMON, but current must be limited to 2mA.
Note 2: INC and ON can be pulled below ground. Limiting the current to 2mA ensures that these pins are never lower than about -0.8V.
IN to GND ............................................................................+15V
STAT, OUTC, LLMON, AUXVCC to GND ...............-0.3V to +14V
GATE to GND ..............................................-0.3V to (VIN + 8.5V)
GATE to LLMON (Note 1).........................................-1V to +8.5V
INC, ON to GND (Note 2) .........................................-1V to +14V
CEXT to GND...............................................-8.5V to (VIN + 0.3V)
CSPD, CTON,
REF to GND ...........-0.3V to the lower of (VIN + 0.3V) or +12V
VSENSE, RTH, CTIM to GND.......................-0.3V to (VIN + 0.3V)
Current into INC, ON (Note 2) ............................................±2mA
Current into Any Other Pin ...............................................±50mA
Continuous Power Dissipation (TA= +70°C)
8-Pin SO (derate 5.9mW/°C above +70°C)..................471mW
16-Pin QSOP (derate 8.3mW/°C above +70°C)...........667mW
16-Pin SO (derate 8.7mW/°C above +70°C)................696mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
POWER SUPPLIES
Input Voltage Range VIN 2.7
13.2
V
Supply Current IQVON = VIN 0.6 1 mA
CURRENT CONTROL
TA = +25°C 455055
Slow Comparator Threshold
VSC
,
TH
VIN - VSENSE
TA = TMIN to TMAX 43.5
56 mV
CSPD = floating 10 20 40 μs
Slow Comparator Response
Time tCSPD CSPD = 100nF to GND 10 20 40 ms
TA = +25°C 455055
5kΩ on
RTH to
VIN
TA = TMIN to TMAX 43.5
56
TA = +25°C 675 750 825
75kΩ
on RTH
to VIN
TA = TMIN to TMAX
650 840
MAX4273
only
RTH = GN D
Fast Comparator Threshold
VFC
,
TH
MAX4271/MAX4272 180 200 220
mV
Fast Comparator Response
Time tFCD 10mV overdrive, from overload condition to
gate discharging 350 ns
SENSE Input Bias Current
IB
,
SENSE
VSENSE = VIN 0.2 10 μA
MOSFET DRIVER
MAX4271/MAX4272 CTIM = 100nF 21 31 41
MAX4273 CTON = 100nF 21 31 41 ms
Startup Period
(Notes 4, 5)
tSTART
No capacitor 5.5 μs
Gate Charge Current IGATE GATE = IN (Note 6) 100 μA
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VIN = +2.7V to +13.2V, TA= -40°C to +85°C, unless otherwise noted. Typical values are at VIN = +5V and TA= +25°C.) (Note 3)
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX
UNITS
Slow Turn-Off Time
tSLOW
,
OFF
Time from trigger to VGATE < 0.1V
(triggered by either the ON input or the
slow comparator), CGATE = 1000pF to
GND
60 µs
Fast Turn-Off Time
tFAST
,
OFF
Time from current overload to VGATE < 0.1V
(triggered by the fast comparator, during
normal operation), CGATE = 1000pF to GND
15 μs
Maximum Gate Protection
Voltage
Voltage at which internal zener clamp
circuitry is triggered, measured with
respect to VIN (MAX4271/MAX4272),
measured with respect to VLLMON
(MAX4273)
6.7 7.5 V
VIN ≥ 5V 5
Minimum Gate Drive Voltage
Measured with
respect to VIN,
IGATE = 8.5µA VIN ≥ 2.7V 2.7
V
During fast discharge, due to a fast
comparator fault in normal operation 0.4 1
2.75
mA
During startup (current regulation provided
by fast comparator) 25 70 195
Gate Discharge Current
IGATE
,
DIS
During normal discharge, due to a slow
comparator fault in normal mode, or by ON
going low
75 200 550
μA
LLMON Overvoltage Threshold
Startup is initiated only after VLLMON is less
than this voltage (MAX4273) 0.1 V
GATE Overvoltage Threshold Startup is initiated only after VGATE is less
than this voltage 0.1 0.6 V
LLMON Impedance Im p ed ance to GN D , after a faul t ( M AX 4273) 1 kΩ
REFERENCE (MAX4273)
Output Voltage VREF No load, VIN = 5V
1.164
1.2
1.236
V
Line Regulation
ΔVREF
,
LINE
2.7V ≤ VIN ≤ 13.2V, no load 1 8 mV
Load Regulation ΔVREF,
LOAD IREF = 0 to 100μA, VIN = 5V 0.6 3 mV
ON AND RESET COMPARATORS
Threshold Voltage VIN = 5V, rising threshold at ON or INC
0.575
0.6
0.625
V
Hysteresis VHYST 3mV
Power-Supply Rejection Ratio PSRR 2.7V ≤ VIN ≤ 13.2V ±1
mV/V
10mV overdrive, ON going positive or
negative, INC going negative 10 μs
Propagation Delay
tD
,
COMP
INC going positive 100 150 200 ms
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
4 _______________________________________________________________________________________
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Input Voltage Range
Input can be driven to the absolute
maximum limit without false output
inversion
-0.1
13.2
V
Input Bias Current
IB
,
COMP 0.001
1μA
ON Pulse Width Low (Note 7)
tRESTART
To unlatch a fault MAX4271, MAX4273 with
CTIM = IN 20 μs
DIGITAL OUTPUTS (STAT, OUTC)
Output Leakage Current VSTAT ≤ 13.2, VOUTC ≤ 13.2 1 μA
Output Voltage Low VOL ISINK = 1mA 0.4 V
RETRY TIMING (MAX4272, MAX4273)
Retry Timeout Period
tRETRY
100nF capacitor on CTIM (Note 5) 0.5 1 2 s
Default Retry
Timeout Period
tRETRY
(default)
CTIM = no connection 176 µs
UNDERVOLTAGE LOCKOUT (UVLO)
Threshold
VUVLO
Startup is initiated when this threshold is
exceeded at IN
2.25 2.67
V
Hysteresis
V
U V LO
,
H YS T
100 mV
Delay
tD
,
UVLO
Time the input voltage must exceed
undervoltage lockout before startup is
initiated
100 150 200 ms
ELECTRICAL CHARACTERISTICS (continued)
(VIN = +2.7V to +13.2V, TA= -40°C to +85°C, unless otherwise noted. Typical values are at VIN = +5V and TA= +25°C.) (Note 3)
Note 3: All devices are 100% tested at TA= +25°C. All temperature limits are guaranteed by design.
Note 4: Startup period is the time during which the slow comparator is ignored and the fast comparator regulates the sense current.
It is measured from the time ON is brought high.
Note 5: Inferred from test with CTON = 10nF (MAX4273) and CTIM = 1nF.
Note 6: The current available at GATE is a function of VGATE (see Typical Operating Characteristics).
Note 7: Guaranteed by design.
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
_______________________________________________________________________________________ 5
Typical Operating Characteristics
(VIN = 5V, RSENSE = 100mΩ, CBOARD = 47µF, TA = +25°C, unless otherwise noted.)
0
0.3
0.2
0.1
0.5
0.4
0.9
0.8
0.7
0.6
1.0
02468101214
SUPPLY CURRENT vs. INPUT VOLTAGE
MAX4271/3-01
VIN (V)
SUPPLY CURRENT (mA)
ON = VIN
IGATE = 10μA
ON = GND
-40 -15 10 35 60 85
SUPPLY CURRENT vs. TEMPERATURE
MAX4271/3-02
TEMPERATURE (°C)
0
0.3
0.2
0.1
0.5
0.4
0.9
0.8
0.7
0.6
1.0
SUPPLY CURRENT (mA)
ON = VIN
VIN = 12V
VIN = 5V
VIN = 3V
180
200
190
220
210
230
240
18
20
19
22
21
23
24
0682 4 10 12 14
SLOW COMPARATOR
RESPONSE TIME vs. INPUT VOLTAGE
MAX4271/3-03
VIN (V)
tCSPD (μs)
tCSPD (ms)
CSPD = 110nF
TIME IN ms
CSPD = 0
TIME IN μs
49.0
49.6
49.4
49.2
50.0
49.8
50.8
50.6
50.4
50.2
51.0
02468101214
SLOW COMPARATOR THRESHOLD
vs. INPUT VOLTAGE
MAX4271/3-04
VIN (V)
VSC,TH (mV)
TA = -40°C
TA = +25°C
TA = +85°C
200
250
350
300
400
450
1 10 100 1000
FAST COMPARATOR RESPONSE TIME
vs. OVERDRIVE VOLTAGE
MAX4271/3-05
OVERDRIVE VOLTAGE (mV)
RESPONSE TIME (ns)
VIN = 12V
VIN = 5V
VIN = 3V
200
300
400
350
450
500
-40 10-15 35 60 85
FAST COMPARATOR RESPONSE TIME
vs. TEMPERATURE
MAX4271/3-06
TEMPERATURE (°C)
RESPONSE TIME (ns)
VIN = 12V
VIN = 5V
VIN = 3V
250
190
196
194
192
200
198
208
206
204
202
210
FAST COMPARATOR THRESHOLD
vs. INPUT VOLTAGE
MAX4271/3-07
VFC,TH (mV)
02468101214
VIN (V)
TA = -40°C
TA = +25°C
TA = +85°C
0.1
1
1k
100
10
10k
100k
0.01 10.1 10 100 1000
TIME TO FAST DISCHARGE GATE
vs. CGATE
MAX4271/3-08
CGATE (nF)
TIME TO DISCHARGE GATE (μs)
VIN = 12V
VIN = 5V
VIN = 3V
NO EXTERNAL MOSFET
DISCHARGE TO VGATE = 0.1V
250
270
310
290
330
350
042 6 8 101214
STARTUP PERIOD
vs. INPUT VOLTAGE
MAX4271/3-09
VIN (V)
tSTART (μs)
25
27
31
29
33
35
tSTART (ms)
CTIM = 100nF
TIME IN ms
CTIM = 1nF
TIME IN μs
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
6 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VIN = 5V, RSENSE = 100mΩ, CBOARD = 47µF, TA = +25°C, unless otherwise noted.)
0
0.4
0.2
0.8
0.6
1.0
1.2
1.6
1.4
1.8
02468101214161820
FAST GATE DISCHARGE CURRENT
vs. VGATE
MAX4271/3-10
VIN (V)
FAST GATE DISCHARGE CURRENT (mA)
VIN = 12V
VIN = 3V
VIN = 5V
0
60
40
20
80
100
120
0862 4 10 12 14 16 18 20
GATE CHARGE CURRENT
vs. GATE VOLTAGE
MAX4271/3-11
VGATE (V)
IGATE (μA)
VIN = 12V
VIN = 5.0V
VIN = 3.0V
0
50
25
100
75
125
150
-40 10 35-15 60 85
GATE CHARGE CURRENT
vs. TEMPERATURE
MAX4271/3-12
TEMPERATURE (°C)
IGATE (μA)
VIN = 12V
VGATE = 0
VIN = 5V
VIN = 3V
0
5
15
10
20
25
042 6 8 101214
GATE VOLTAGE vs. INPUT VOLTAGE
MAX4271/3-13
VIN (V)
VGATE (V)
IGATE = 10μA
TA = +85°C
TA = +25°C
TA = -40°C
0
100
50
150
300
350
250
200
400
0 468102 1214161820
SLOW GATE DISCHARGE CURRENT
vs. GATE VOLTAGE
MAX4271/3-13a
VGATE (V)
IGATE (μA)
VIN = 12V
VIN = 3V
TRIGGERED BY A FAULT
OR BY ON FALLING
VIN = 5V
0.01 0.1 1 10 100 1000
TIME TO CHARGE GATE
vs. CGATE
MAX4271/3-14
CGATE (nF)
TIME TO CHARGE GATE (ms)
1000
0.001
0.01
1
0.1
100
10
NO EXTERNAL MOSFET
VIN = 12V
TO VGATE = 17V
VIN = 5V
TO VGATE = 10V
VIN = 3V
TO VGATE = 6V
1.0
2.5
2.0
1.5
3.0
3.5
4.0
3.0 3.83.63.2 3.4 4.0 4.2 4.4 4.6 4.8 5.0
FAST GATE DISCHARGE CURRENT
vs. VIN
MAX4271/3-15
FAST GATE DISCHARGE CURRENT (mA)
RISING VIN
FALLING VIN
VIN (V)
0
100
50
200
150
350
300
250
400
-40 10-15 35 60 85
SLOW GATE DISCHARGE CURRENT
vs. TEMPERATURE
MAX4271/3-16
TEMPERATURE (°C)
IGATE (μA)
VIN = 3V
VIN = 5V, 12V
VGATE = VIN
TRIGGERED BY A FAULT
OR BY ON FALLING
0.01 0.1 1 10 100 1000
TIME TO SLOW DISCHARGE GATE
vs. CGATE
MAX4271/3-17
CGATE (nF)
TIME TO DISCHARGE GATE (ms)
1000
0.001
1
0.1
0.01
10
100
VIN = 12V
VIN = 5V
VIN = 3V
DISCHARGE TO VGATE = 0.1V
NO EXTERNAL MOSFET
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
_______________________________________________________________________________________ 7
Typical Operating Characteristics (continued)
(VIN = 5V, RSENSE = 100mΩ, CBOARD = 47µF, TA = +25°C, unless otherwise noted.)
1.0
1.4
1.2
1.8
1.6
2.2
2.0
2.4
-40 10-15 356085
FAST GATE DISCHARGE CURRENT
vs. TEMPERATURE
MAX4271/3-18
TEMPERATURE (°C)
FAST GATE DISCHARGE CURRENT (mA)
VGATE = VIN
VIN = 3V
VIN = 5V, 12V
CBOARD = 470μF, RSENSE = 100mΩ,
CGATE = 0
ILOAD
(1A/div)
VOUT
(2V/div)
VGATE
(2V/div)
0
50μs/div
MAX4271/MAX4272
TURN-OFF TIME (CBOARD = 470μF)
MAX4271/3-19
ON
0
CBOARD = 470μF, RSENSE = 100mΩ,
CGATE = 22nF, RS = 0
ILOAD
1A/div
VOUT
2V/div
VGATE
2V/div
0
0
200μs/div
MAX4271/MAX4272
TURN-OFF TIME
(EXTERNAL CGATE = 22nF, CBOARD = 470μF)
MAX4271/3-20
ON
0.595
0.597
0.601
0.599
0.603
0.605
042 6 8 101214
ON COMPARATOR THRESHOLD
vs. INPUT VOLTAGE
MAX4271/3-21
VIN (V)
ON COMPARATOR THRESHOLD (V)
RISING
FALLING
0.5950
0.6000
0.5975
0.6050
0.6025
0.6075
0.6100
-40 35 60-15 10 85
ON-COMPARATOR THRESHOLD
vs. TEMPERATURE
MAX4271/3-22
TEMPERATURE (°C)
ON COMPARATOR THRESHOLD (V)
RISING
FALLING
}
}
VIN = 12V
VIN = 5V
VIN = 3V
2.30
2.40
2.35
2.50
2.45
2.55
2.60
-40 35 60-15 10 85
UVLO THRESHOLD VOLTAGE
vs. TEMPERATURE
MAX4271/3-26
TEMPERATURE (°C)
UVLO THRESHOLD (V)
RISING
FALLING
140
145
150
155
160
UVLO DELAY vs. TEMPERATURE
MAX4271/3-27
TEMPERATURE (°C)
UVLO DELAY (ms)
-40 35 60-15 10 85
VIN = 3V
VIN = 5V, 12V
MAX4273
TURN-OFF TIME
(EXTERNAL CGATE = 22nF, CBOARD = 470μF)
MAX4271/3-20a
ILOAD
1A/div
0
ON
VOUT
2V/div
VGATE
2V/div
0
20μs/div
MAX4273
TURN-OFF TIME
(CBOARD = 470μF)
MAX4271/3-20b
VOUT
2V/div
VGATE
2V/div
0
ILOAD
1A/div
0
ON
50μs/div
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
8 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VIN = 5V, RSENSE = 100mΩ, CBOARD = 47µF, TA = +25°C, unless otherwise noted.)
0.625
0.605
0.615
0.595
0.585
0.575
4106 8 12 14 16
INC THRESHOLD vs. INPUT VOLTAGE
MAX4271/3-28
INPUT VOLTAGE (V)
THRESHOLD (V)
RISING
FALLING
600
610
608
606
604
602
614
612
618
616
620
-40 10-15 356085
INC THRESHOLD vs. TEMPERATURE
MAX4271/3-29
TEMPERATURE (°C)
THRESHOLD (mV)
RISING
FALLING
1.2020
1.2024
1.2022
1.2030
1.2028
1.2026
1.2038
1.2036
1.2034
1.2032
1.2040
3795 111315
MAX4273
REFERENCE VOLTAGE
vs. INPUT VOLTAGE
MAX4271/3-30
INPUT VOLTAGE (V)
REFERENCE VOLTAGE (V)
1.2000
1.2005
1.2010
1.2015
1.2020
1.2025
1.2030
1.2035
1.2040
-40 -15 10 35 60 85
REFERENCE VOLTAGE
vs. TEMPERATURE
MAX4271/3-31
TEMPERATURE (°C)
REFERENCE VOLTAGE (V)
920
930
925
940
935
945
950
3579111315
RETRY TIMEOUT PERIOD
vs. INPUT VOLTAGE
MAX4271/3-32
INPUT VOLTAGE (V)
RETRY TIMEOUT (ms)
CTIM = 100nF
965
970
975
980
985
990
995
-40 -15 10 35 60 85
RETRY TIMEOUT PERIOD
vs. TEMPERATURE
MAX4271/3-33
TEMPERATURE (°C)
RETRY PERIOD (ms)
12V
5V
3V
CBOARD = 470μF, RSENSE = 100mΩ,
CTIM = 10nF, CGATE = 0
ILOAD
1A/div
VOUT
2V/div
VGATE
2V/div
ON
500μs/div
STARTUP TIME (CBOARD = 470μF)
MAX4271/3-34
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
_______________________________________________________________________________________ 9
Typical Operating Characteristics (continued)
(VIN = 5V, RSENSE = 100mΩ, CBOARD = 47µF, TA = +25°C, unless otherwise noted.)
CBOARD = 0, RSENSE = 100mΩ,
CGATE = 0, RS = 0
ILOAD
1A/div
VOUT
2V/div
VGATE
2V/div
0
50μs/div
TURN-OFF TIME (CBOARD = 0)
MAX4271/3-37
ON
0
Pin Description
CBOARD = 0, RSENSE = 100mΩ,
CTIM = 10nF, CGATE = 0
VOUT
2V/div
VGATE
2V/div
ON
100μs/div
STARTUP TIME (CBOARD = 0)
MAX4271/3-35
PIN
MAX4271
MAX4272
MAX4273
NAME FUNCTION
— 1 RTH
Current-Sense Threshold Setting Input. Connect a resistor from RTH to VIN to set the
fast comparator threshold. Bypass to VIN with 0.1μF. Connect RTH to VIN to disable
both the fast comparator and current regulation at startup. Short RTH to GND for a
200mV threshold. See Fast Comparator Threshold section.
—2
AUXVCC
Auxiliary Supply Input. Supply input for short-circuit switchover. To use this, connect a
1μF capacitor from AUXVCC to GND; otherwise, leave floating. See Auxiliary VCC
section.
13IN
Input Voltage. Connect to +2.7V to +13.2V supply; 15V absolute maximum voltage
rating.
2 4 SENSE Current-Sense Resistor Voltage Input. RSENSE is connected from IN to SENSE.
3 5 GATE Gate Drive Output. Connect to gate of external N-channel pass transistor.
—6
CEXT External Gate Capacitance Connection. Connect a capacitor from CEXT to GATE to
increase the gate charging time. This pin goes high impedance during a fast
comparator fault for fast discharge.
—7
LLMON
Load Line Monitor. Connect to the source of the external N-channel MOSFET. The
external FET is turned on only when the load voltage is less than 100mV.
4 8 GND Ground
— 9 CTON Startup Timer Input. Leave floating or connect the timing capacitor from CTON to GND.
See Startup and Retry Timers section.
5 10 CSPD Slow Comparator Speed Setting. Leave floating or connect the timing capacitor from
CSPD to GND. See Slow Comparator Response Time section.
Detailed Description
The MAX4271/MAX4272/MAX4273 are circuit breaker
ICs designed for hot-swap applications where a line
card is inserted into a live backplane. Normally, when a
line card is plugged into a live backplane, the card’s
discharged filter capacitors provide a low impedance
that can momentarily cause the main power supply to
collapse. The MAX4271/MAX4272/MAX4273 are
designed to reside either in the backplane or in the
removable card to provide inrush current limiting and
short-circuit protection. This is achieved by using an
external N-channel MOSFET, an external current-sense
resistor, and two on-chip comparators. Figures 1 and 2
show the functional diagrams.
The timing and voltage levels for several critical parame-
ters can be adjusted with external resistors, external
capacitors, or by pin strapping. The timing components
are optional; without them, the part is set to its nominal
values, as shown in the Electrical Characteristics. The
parameters that can be adjusted are:
• Current-limit threshold
• Slow comparator response time
• Startup timer
• Fast comparator threshold
• Autoretry timeout period (time the part is shut down
after an overcurrent event)
• Fault management (latched/autoretry)
• Current overload threshold
Startup Mode
CTIM (MAX4271/MAX4272) or CTON (MAX4273) sets
the startup period (see Startup and Retry Timers). The
startup period begins after three conditions are met:
1) 150ms after VIN exceeds the UVLO threshold (see
Over/Undervoltage Lockouts)
AND
2) 10µs after VON >0.6V
AND
3) The device is no longer in retry mode.
During startup, the slow comparator is disabled and the
inrush current can be limited in two ways:
1) Slow ramping of the current to the load by control-
ling the external MOSFET gate voltage
OR
2) Limiting the current to the load by regulating the volt-
age across the external current-sense resistor
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
10 ______________________________________________________________________________________
PIN
MAX4271
MAX4272
MAX4273
NAME FUNCTION
6 11 CTIM
Startup and Retry Timers Input. Controls the startup time and the autoretry time (32x
startup time) in the MAX4272, only the autoretry time in the MAX4273, and only the
startup time in the MAX4271. Leave floating or connect the timing capacitor from CTIM
to GND. Connect to IN for latched mode (this prevents autoretry in MAX4273). See
Startup and Retry Timers section.
7 12 STAT Status Output. High indicates startup completed with no fault (Table 1). STAT is an
open-drain output.
813ON
ON Comparator Input. Connect high for normal operation; connect low to force the
MOSFET off. Comparator threshold VTH,ON = 0.6V allows for precise control over
shutdown feature. Pulse ON low for 20μs min to unlatch after a fault (MAX4273 in
latched mode, or MAX4271). Negative pulses are ignored during autoretry (MAX4273
in autoretry mode, or MAX4272). See ON and Reset Comparators section.
— 14 REF 1.2V Reference Output. Do not bypass with a capacitor to GND.
— 15 INC Uncommitted Comparator Input. Controls OUTC.
— 16 OUTC Uncommitted Comparator Output. OUTC goes high 150ms after INC goes high. OUTC
goes low immediately after INC goes low. OUTC is an open-drain output.
Pin Description (continued)
Unlike other circuit breaker ICs, the MAX4271/
MAX4272/MAX4273 regulate the current to a preset
level instead of completely turning off the external
N-FET if an overcurrent condition occurs during startup.
In startup mode, the gate drive current is limited to
100µA and decreases with the increase of the gate
voltage (see Gate Charge Current vs. Gate Voltage in
the Typical Operating Characteristics). This allows the
controller to slowly enhance the MOSFET. If the fast
comparator detects an overcurrent, the gate voltage is
momentarily discharged with a fixed 70µA current until
the load current through the sense resistor (RSENSE)
decreases below its threshold point. This effectively
regulates the inrush current during startup. Figure 3
shows the startup waveforms. STAT goes high at the
end of the startup period if no fault condition is present.
Normal Operation (DualSpeed/BiLevel)
In normal operation (after the startup timer has
expired), protection is provided by turning off the exter-
nal MOSFET when a fault condition is encountered.
DualSpeed/BiLevel fault protection incorporates two
comparators with different thresholds and response
times to monitor the current:
1)Slow comparator. This comparator has an externally
set response time (from 20µs to seconds) and a fixed
50mV threshold voltage. The slow comparator
ignores low-amplitude momentary current glitches.
After an extended overcurrent condition, a fault is
generated and the MOSFET gate is slowly dis-
charged.
2)Fast comparator. This comparator has a fixed 350ns
response time and a 200mV threshold voltage
(adjustable from 50mV to 750mV in MAX4273). The
fast comparator turns off the MOSFET immediately
after it detects a large amplitude event such as a
short circuit.
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
______________________________________________________________________________________ 11
Figure 1. MAX4271/MAX4272 Functional Diagram
MAX4271
MAX4272 6μA
SLOW COMPARATOR
FAST COMPARATOR
6μA
2.45V
CSPD
CSPD
INPUT
UVLO
LOGIC
CONTROL
DISCHARGE
ENABLE
VIN
STAT
GND
CTIM
CTIM
4μA
0.1V
0.6V
ON
RSENSE
N
M1
GATE
SENSE
IN
GATE
OVLO
ON COMPARATOR
GATE
DRIVE
VSC,TH
50mV
VSC,TH
200mV
150ms
DELAY
ON
VIN RISING
VOUT
VIN
CHARGE
PUMP
(1MHz)
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
12 ______________________________________________________________________________________
Figure 2. MAX4273 Functional Diagram
MAX4273
6μA
VIN
SLOW COMPARATOR
FAST COMPARATOR
6μA
2.45V
INPUT
UVLO
LOGIC
CONTROL
DISCHARGE
ENABLE
STAT
REF REF
1.2V
AUXVCC
AUXVCC
GND
0.1V
0.6V
ON
LLMON
INC
VOUT
RSENSE
VIN
CSPD
N
Q1
GATE
CEXT
CEXT
SENSE
RTH
RTH
IN
OUTPUT
OVLO
0.1V GATE
OVLO
ON COMPARATOR
RESET COMPARATOR
GATE DRIVE
VFC,TH = 50mV
VFC,TH = 200mV
VFC,TH =
50mV TO 750mV
150ms
DELAY
ON
VIN RISING
OUTC
VIN
CTIM
CTIM
4μA
10μA
AUXVCC
VIN
CTON
CTON
4μA
150ms
DELAY ON INC RISING 0.6V
CHARGE PUMP
1MHz
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
______________________________________________________________________________________ 13
In each case, when a fault is encountered, the status
pin (STAT) goes low, and for the MAX4273, the device
discharges the output voltage through a 1kΩresistor
from LLMON to GND. After a fault, the MAX4271 stays
latched off and the MAX4272 enters retry mode, while
the MAX4273 has selectable latched or retry mode.
Figure 4 shows the waveforms of a fault condition.
BiLevel Fault Protection
Slow Comparator
The slow comparator is disabled at startup while the
external MOSFET is turning on. This allows the part to
ignore the higher-than-normal inrush current charging
the board capacitors when a card is first plugged in.
If the slow comparator detects an overload condition
while in normal operation (after startup is completed), it
turns off the external MOSFET by discharging the gate
capacitance with a 200µA current. The slow compara-
tor threshold is set at 50mV and has a default delay of
20µs (CSPD floating), allowing it to ignore power-sup-
ply glitches and noise. The response time can be
lengthened with an external capacitor at CSPD (Figure
10).
If the overcurrent condition is not continuous, then the
duration above the threshold minus the duration below
must be greater than 20µs (or the external programmed
value) for the device to trip. When the current is above
the threshold, CSPD is charged with a 6µA current
source. A fault is detected when CSPD is charged to
the trip point of 1.2V. Therefore, a pulsing current with a
duty cycle of 50% or greater (i.e., the current is above
the threshold level > 50% of the time) is considered a
fault condition even if it is never higher than the thresh-
old for longer than the slow comparator’s set response
time.
The discharge rate depends on the N-FET gate capaci-
tance and the external capacitance at GATE. In the
MAX4273, CEXT remains connected and capacitance
to this point has to be discharged by the same current.
This increases the discharge time. Once the fault con-
dition is detected, the STAT pin goes low and the
device goes into retry or latched mode.
Fast Comparator
The fast comparator behaves differently according to
the operating mode.
During startup, the fast comparator is part of a simple
current regulator. When the sensed current is above
the fast comparator threshold, the gate is discharged
with a 70µA current source. When the sensed current
drops below the threshold, the charge pump turns on
again. The sensed current will rise and fall near the
threshold due to the fast comparator and charge-pump
propagation delay. The gate voltage will be roughly
sawtooth shaped, and the load current will present a
20% ripple. The ripple can be reduced by adding a
capacitor from GATE to GND.
Figure 3. Startup Waveforms
t
START
t
ON
2.7V TO 6V
VGATE
IFAST, SET
VGATE
STAT
ON
VTH
VOUT
CBOARD = LARGE
CBOARD = 0
VOUT
ILOAD
Figure 4. Response to a Fault Condition
t
OFF
VGATE
STAT
VOUT
ILOAD
ILIM
2.7V TO 6V
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
14 ______________________________________________________________________________________
Table 1. Status Output Truth Table
If the sensed current is still high after the startup timer
expires, the MOSFET gate is discharged completely as
described below.
In normal operation (after startup), the fast comparator is
used as an emergency off switch. If the load current
reaches the fast comparator threshold, the device quickly
forces the MOSFET off completely. This could happen in
the event of a serious current overload or a dead short.
The fast comparator has a 350ns response time and dis-
charges GATE with a 1mA current. Given a 1000pF gate
capacitance and 12V gate voltage, the MOSFET will be
off in about 12µs. Any additional capacitance connected
between GATE and GND to slow down the startup time
also increases the turn-off time.
In the MAX4273, CEXT goes high impedance during
the fast discharge. This reduces the effective capaci-
tance on GATE if a capacitor is used between GATE
and CEXT, and allows the MOSFET to quickly turn off.
In turn, this allows adjustment of the MOSFET charging
time without affecting the fast discharge rate, although
it does affect the slow discharge rate.
The MAX4271/MAX4272 fast comparator threshold is set
to four times the slow comparator threshold (i.e., 200mV).
The MAX4273 fast comparator threshold is set to 200mV
by connecting RTH to GND, is disabled by connecting
RTH to IN, or is adjustable by an external resistor con-
nected to IN (see Fast Comparator Threshold (RTH)).
Latched/Autoretry
The MAX4271 MOSFET driver stays latched off after a
fault condition until it is reset by a negative-going pulse
on the ON pin. The MAX4272 is periodically turned on
after a fault condition with a timeout duration set by an
external timing capacitor on CTIM. The MAX4273 has a
selectable latched mode or retry mode. Connect CTIM
to IN to set the device in latched mode, or use an exter-
nal capacitor at CTIM to set the retry timeout.
Pulse ON low for 20µs (min) to restart after a fault
(MAX4271/MAX4273 in latched mode). Negative pulses
are ignored during autoretry (MAX4273 in autoretry
mode, or MAX4272).
The capacitor on CTIM affects the MAX4272’s retry
timeout period (time the part is shut down after an over-
current event) and the startup time (see the Electrical
Characteristics). The retry timeout period is fixed at 32
times the startup time in order to minimize power dissi-
pation in the external MOSFET in case of a short-circuit
condition (see MOSFET Thermal Considerations). This
is not an issue for parts latched off during a fault condi-
tion since they stay off until commanded on. The
MAX4273 configured in retry mode has a separate
startup timer capacitor (CTON) and retry timeout
capacitor (CTIM). This allows the user to change the
ratio between startup time and retry timeout period.
Status Output
The status output is an open-drain output that goes low
under the following conditions:
• During the UVLO delay period
• In startup
• Forced off (ON <0.6V)
• In an overcurrent condition
• In the retry timeout period (or latched off, for the
latched parts)
STAT is high only if the part is in normal mode and no
faults are present (Table 1). Figure 5 shows the status
(STAT) output timing diagram.
Over/Undervoltage Lockouts
The UVLO prevents the MAX4271/MAX4272/MAX4273
from turning on the external MOSFET until VIN exceeds
the lockout threshold (2.25V min) for 150ms. The UVLO
protects the external MOSFET from insufficient gate
drive voltage. The 150ms timeout ensures that the
board is fully plugged into the backplane and that VIN
IN
UVLO DELAY
PERIOD
PART IN
STARTUP
ON PIN OVERCURRENT
CONDITION
PART IN RETRY-TIMEOUT
PERIOD (OR LATCHED OFF DUE TO
OVERCURRENT CONDITION)
STAT PIN
(STATUS)
Yes X X X X Low
X Yes X X X Low
X X Low X X Low
X X X Yes X Low
X X X X Yes Low
No No High No No High
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
______________________________________________________________________________________ 15
is stable. Any input voltage transient at IN below the
UVLO threshold will reset the device and initiate a start-
up sequence.
These devices also have an overvoltage lockout
(OVLO) feature that prevents the device from restarting
after a fault condition if the discharge has not been
completed. VGATE has to be discharged to below 0.1V.
Additionally, the MAX4273 LLMON pin discharges the
load line with a 1kΩpulldown and prevents startup until
the load voltage is below 0.1V.
Since the MAX4271/MAX4272 do not monitor the output
voltage, a startup sequence can be initiated while the
board capacitance is still charged.
A large board capacitance or a short startup period may
prevent the MAX4272 from charging completely in one
startup period. The MAX4272 responds to these condi-
tions by charging the capacitor with bursts defined by a
tON duty cycle and a period of tON + tRETRY. The charg-
ing will be complete after several retries unless the resis-
tive load or current load excessively discharges the
board capacitance during the retry timeout. This feature
applies to the MAX4273 if LLMON is left floating or is
connected to GND. To prevent multiple charging bursts,
ensure that the tON timer exceeds the minimum time
required to complete the charge of the board capaci-
tance (see Component Selection).
Gate Overvoltage Protection
New-generation MOSFETs have an absolute maximum
rating of ±8V for the gate-to-source voltage (VGS). To
protect these MOSFETs, the MAX4271/MAX4272 limit the
gate-to-drain voltage (the MAX4273 limits the gate-to-
source voltage) to +7.5V with an internal zener diode. No
protection is provided for negative VGS (MAX4271/
MAX4272). If GATE can be discharged to ground faster
than the output voltage, an external small-signal protec-
tion diode (D1) can be used, as shown in Figure 6. The
MAX4273 has the protection diode internal.
Applications Information
Component Selection
N-Channel MOSFET
Select the external N-channel MOSFET according to
the application’s current level. Table 2 lists some rec-
ommended components. The MOSFET’s on-resistance
(RDS(ON)) should be chosen low enough to have a min-
imum voltage drop at full load to limit the MOSFET
power dissipation. High RDS(ON) can cause output rip-
ple if the board has pulsing loads or triggers an exter-
nal undervoltage reset monitor at full load. Determine
the device power-rating requirement to accommodate
a short circuit on the board at startup with the device
Figure 5. Status (STAT) Output Timing Diagram
O
1.2V
tSTART
O
O
STAT
CTIM
(CTON)*
ON
FAULT CONDITION,
OR ON FALLING
EDGE
NO FAULT CONDITIONS PRESENT
*MAX4273 ONLY
VIN
VIN
Table 2. Recommended N-Channel
MOSFETs
PART
NUMBER
MANUFACTURER
DESCRIPTION
IRF7413 11mΩ, 8 SO, 30V
IRF7401 22mΩ, 8 SO, 20V
IRL3502S
International
Rectifier 6mΩ, D2PAK, 20V
MMSF3300 20mΩ, 8 SO, 30V
MMSF5N02H 30mΩ, 8 SO, 20V
MTB60N05H
Motorola
14mΩ, D2PAK, 50V
FDS6670A 10mΩ, 8 SO, 30V
NDS8426A 13.5mΩ, 8 SO, 20V
FDB8030L
Fairchild
4.5mΩ, D2PAK, 30V
Figure 6. External Gate-Source Protection
D1
GATE
RSENSE
VOUT
VGD
VGS
CBOARD
IN
SENSE
M1
N
MAX4271
MAX4272
GATE DRIVE
CHARGE PUMP
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
16 ______________________________________________________________________________________
configured in automatic retry mode (see MOSFET
Thermal Considerations).
Using the MAX4271/MAX4273 in latched mode allows
the consideration of MOSFETs with higher RDS(ON) and
lower power ratings. A MOSFET can typically withstand
single-shot pulses with higher dissipation than the
specified package rating. Low MOSFET gate capaci-
tance is not necessary since the inrush current limiting
is achieved by limiting the gate dv/dt. Table 3 lists
some recommended manufacturers and components.
Sense Resistor
The slow comparator threshold voltage is set at 50mV.
Select a sense resistor that causes a 50mV voltage
drop at a current level above the maximum normal
operating current; typically, set the overload current at
1.2 to 1.5 times the nominal load current. The fast com-
parator threshold is typically set at 200mV. This will set
the fault current limit at four times the overload current
limit. The MAX4273 fast comparator threshold can be
set between 50mV and 750mV; see Table 4 for a
detailed listing.
Choose the sense resistor power rating according to
the device configuration. If no retry mode is selected,
PRSENSE = (IOVERLOAD)2x RSENSE; if retry is selected,
then PRSENSE = (IFAULT)2x RSENSE x (tON/tRETRY).
Fast Comparator Threshold (RTH) (MAX4273)
The fast comparator threshold is determined by the
external resistor connected at RTH. To select threshold
voltages between 50mV and 750mV, use resistor val-
ues between 5kΩand 75kΩaccording to Figure 7.
Resistor values between 200Ωand 5kΩare not recom-
mended. Setting the threshold voltage of the fast com-
parator below 50mV will effectively override the slow
comparator operation. The MAX4273 fast comparator
can be disabled by shorting the RTH pin to VIN (VIN -
25mV or less). Ground RTH to set the threshold to
200mV internally.
Startup and Retry Timers (CTIM, CTON)
The startup (tSTART) and retry (tRETRY) timers are deter-
mined by the capacitors connected at CTIM and
CTON. The capacitor connected to CTIM has two func-
tions for the three devices as follows:
Table 4. Current Levels vs. RSENSE
RSENSE (mΩ) PART NUMBER OVERLOAD THRESHOLD
SET BY SLOW COMPARATOR (A)
FAULT CURRENT THRESHOLD
SET BY FAST COMPARATOR (A)
MAX4271/MAX4272 5 20
10 MAX4273 5 5 to 75
MAX4271/MAX4272 1 4
50 MAX4273 1 1 to 15
MAX4271/MAX4272 0.5 2
100 MAX4273 0.5 0.5 to 7.5
Table 3. Component Manufacturers
COMPONENT MANUFACTURER PHONE WEB
Dale-Vishay 402-564-3131 www.vishay.com
Sense Resistors IRC 704-264-8861 www.irctt.com
Fairchild 888-522-5372 www.fairchildsemi.com
International Rectifier 310-322-3331 www.irf.com
MOSFETS
Motorola 602-244-3576 www.mot-sps.com/ppd/
DEVICE CTIM FUNCTION
MAX4271 Startup time
MAX4272 Startup time and sets retry timer
MAX4273 Sets retry timer
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
______________________________________________________________________________________ 17
CTON determines the maximum time allowed to com-
plete turn-on for the MAX4273. The default values for
turn-on time (tON) and tRETRY are chosen by leaving
these pins floating; they are 10µs and 320µs, respec-
tively. These are also the minimum values (not con-
trolled and dependent on stray capacitance). Longer
timings are determined by the size of the capacitor
according to Figure 8, and can be determined in Table
5, which lists the startup and retry timing parameters.
Set the tON timer long enough to allow for the MOSFET to
be enhanced and the load capacitor to be charged com-
pletely .
There are two ways of completing the startup sequence.
Case A describes a startup sequence that does not use
the current-limiting feature and slowly turns on the MOS-
FET by limiting the gate dv/dt. Case B uses the current-
limiting feature and turns on the MOSFET as fast as
possible while still preventing a high inrush current.
Case A. Startup Without Current Regulation
There are three ways to turn on the MOSFET without
reaching the fast comparator current limit:
1) If the board capacitance is small, the inrush current
is low.
2) If the gate capacitance is high, the MOSFET turns on
slowly.
3) The fast comparator can be disabled (MAX4273
only).
In all three cases, tON is determined only by the charge
required to enhance the MOSFET. Effectively, the small
gate-charging current limits the output voltage dv/dt.
This time can be extended by connecting an external
capacitor between GATE and GND (MAX4271/
MAX4272) (Figure 9) or between GATE and CEXT
(MAX4273). The turn-on time is dominated by the exter-
nal gate capacitance if this value is considerably higher
than the MOSFET gate capacitance. Table 6 shows the
timing required to enhance the recommended MOSFET
with or without the external capacitor; Figure 3 shows
the related waveforms and timing diagrams. (See Time
to Charge Gate vs. CGATE and Startup Time with
CBOARD = 0 in the Typical Operating Characteristics.)
Remember that a high gate capacitance also increases
the turn-off time (tOFF), except in the case of a
MAX4273 fast fault.
If an external gate capacitor is not used, RSis not nec-
essary. RSprevents MOSFET self-oscillations that can
occur when CGATE is high while CBOARD is low.
Electrical characteristics as specified by the manufac-
turer’s data sheet are:
FDS6670A: CISS = 3200pF, QT(MAX) = 50nC, RDS(ON) =
8.2mΩ
IRF7401: CISS = 1600pF, QT(MAX) = 48nC, RDS(ON) =
22mΩ
MMSF5N03HD: CISS = 1200pF, QT(MAX) = 21nC,
RDS(ON) = 40mΩ
Figure 7. Fast Comparator Threshold vs. RTH
0
200
100
400
300
500
600
700
800
0203010 40 50 60 70 80
FAST COMPARATOR THRESHOLD
VOLTAGE vs. RTH
RTH (kΩ)
VTH, FC (mV)
RTH (kΩ) = VTH,FC (mV)/10
INDETERMINATE,
NOT RECOMMENDED FOR
RTH < 5kΩ
DISABLED FOR
RTH < 200Ω
*MAX4273 retry feature disabled by connecting CTIM to VIN.
Table 5. Startup and Retry Timing Parameters
tON tRETRY
PART
DEFAULT (µs)
EXTERNALLY SET
DEFAULT (µs)
EXTERNALLY SET
MAX4271 10 tON (ms) = 0.31 x CTIM (nF) No retry available
MAX4272 10 tON (ms) = 0.31 x CTIM (nF) 320 tRETRY (ms) = 32 x tON = 10 x CTIM (nF)
MAX4273* 10 tON (ms) = 0.31 x CTON (nF) 320 tRETRY (ms) =10 x CTIM (nF)
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
18 ______________________________________________________________________________________
Case B. Startup With Current Regulation
In applications where the board capacitance (CBOARD)
at VOUT is high, the inrush current causes a voltage
drop across RSENSE that exceeds the fast comparator
threshold (VFC,TH). In this case, the current charging
CBOARD can be considered constant and the turn-on
time is determined by:
tON = CBOARD ✕VIN / IFAST,SET
where the maximum load current IFAST,SET = VFC,TH /
RSENSE. Figure 3 shows the waveforms and timing dia-
grams for a startup transient with current regulation. (See
Startup Time (CBOARD = 470µF) in the Typical Operating
Characteristics.) When operating under this condition, an
external gate capacitor is not required. Adding an exter-
nal gate capacitor at GATE to GND reduces the regulat-
ed current ripple but increases tOFF by increasing the
gate delay (td) (Figure 4).
The actual startup time is determined by the longer of
the two timings of Case A and Case B. Set the startup
timer tSTART at 2 ✕tON to guarantee enough time for
the output voltage to settle; also take into consideration
device parameter variation.
Retry
The retry timer defines the dead time before the IC tries
to restart a startup sequence following a fault detection.
This feature is available on the MAX4272/MAX4273.
Before selecting the retry timer value, determine how
long a temporary high-current fault condition may be
present. In the event of a permanent fault, the automat-
ic retry will effectively force current pulses through the
Figure 8. Startup and Retry Timeout
tON AND tRETRY vs.
CTON AND CTIM
CAPACITANCE (nF)
tON AND tRETRY (ms)
10,000
0.1
0.01
1
10
100
1000
0.01 10 1000.1 1 1000
tRETRY vs. CTIM (MAX4272/MAX4273)
tON vs. CTIM (MAX4271/MAX4272)
tON vs. CTON (MAX4273)
Figure 9. Operation with an External Capacitor
M1
CSPD
*OPTIONAL (SEE TEXT)
CTIM
CTIM
GATE
SENSE
GND
CSPD
ON
RSENSE VOUT
CGATE
CBOARD
VIN
IN
RS*
MAX4271
MAX4272
MAX4273
RPULLUP
STAT
Table 6. “No-Overcurrent” Turn-On Timing (Startup Without Current Limit)
MOSFET tON (ms) MOSFET tOFF (ms)
DEVICE CGATE
(nF) VIN = 3V VIN = 5V
VIN = 12V
VIN = 3V VIN = 5V
VIN = 12V
0 0.22 0.16 0.19 0.07 0.13 0.145
Fairchild FDS6670A 22 2.3 2 3.2 0.54 1.1 1.95
0 0.175 0.130 0.16 0.075 0.13 0.16
International Rectifier
IRF7401 22 1.9 1.8 3.5 0.54 1.1 2.0
0 0.101 0.074 0.073 0.033 0.067 0.085
Motorola MMSF5N03HD 22 2.0 1.8 3.2 0.470 1.0 1.95
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
______________________________________________________________________________________ 19
MOSFET with a duty cycle equal to tON/tRETRY and with
a current equal to IFAST,SET. Therefore, particular care
has to be taken when choosing between immediate
retry and board space needed to manage the power
dissipation capabilities of the MOSFET (see Thermal
Considerations). The duty cycle is fixed to 1/32 for the
MAX4272, but can be varied in the MAX4273 by choos-
ing CTIM and CTON independently.
Additional External Gate Capacitance (CEXT)
An external gate capacitance can be connected at
GATE. This increases the time required to enhance the
MOSFET and further limits the output rise time. In the
MAX4271/MAX4272, connect the external capacitor
between GATE and GND. In the MAX4273, the external
capacitor can be connected between GATE and CEXT
or GND. If the capacitor is connected to CEXT, it is dis-
charged to ground during a slow comparator fault but it
is left floating during a fast comparator fault; this allows
the device to turn off the external MOSFET faster during
critical faults. (CEXT is biased at VIN; therefore, use a
nonpolarized capacitor). Capacitance connected from
GATE to CEXT does little to decrease the regulated cur-
rent ripple. Add a small capacitor (5nF) from GATE to
GND. See the charging and discharging time vs. CGATE
graphs in the Typical Operating Characteristics.
Slow Comparator Response Time (CSPD)
The slow comparator threshold is set at 50mV, and its
response time is determined by the external capacitor
connected to CSPD (Figure 10).
A minimum response time of 20µs (typ) is achieved by
leaving this pin floating. This time is determined inter-
nally and is not affected by stray capacitance at CSPD
(up to 100pF).
Set the slow comparator response time to be longer
than the normal operation load transients (see Slow
Comparator).
ON and Reset Comparators
The ON comparator controls the ON/OFF function of
these devices. The ON comparator is a precision volt-
age comparator that can be used for temperature moni-
toring or as an additional UVLO (Figure 11). The
MAX4273 also features an uncommitted delayed com-
parator. This comparator can be used for voltage moni-
toring, power sequencing, or for generating a power-on
reset signal for on-card microprocessors (Figure 12).
Both comparator threshold voltages are set at VREF/2 =
0.6V with a 3mV (typ) hysteresis.
The uncommitted comparator OUTC output is an open-
drain output, and it is asserted low when its input volt-
age (INC) is below the threshold voltage. It goes into a
high-impedance state 150ms after the voltage has risen
above the threshold. The delay for negative-going
edges is 10µs.
Figure 13 shows the MAX4273 used to monitor precise-
ly the temperature of an external device such as the
MOSFET. This configuration uses the uncommitted
comparator to set the UVLO at a higher level by running
its output into the ON comparator’s input.
The ON comparator initiates startup when its input volt-
age (VON) rises above the threshold voltage and turns
off the MOSFET when the voltage falls below the thresh-
old. The propagation delay is 10µs going high or low.
The ON comparator is also used to reset the
MAX4271/MAX4273 (when CTIM = VIN) after a fault
condition (see Latched/Autoretry).
Figure 10. Slow Comparator Response Time vs. CSPD
1000
0.01 0.1 1 10 100 1000
100
10
1
0.1
0.01
SLOW COMPARATOR
RESPONSE TIME vs. CSPD
CSPD (nF)
RESPONSE TIME (ms)
tCSPD (ms) = 0.2 x CSPD (nF)
Figure 11. Temperature Monitoring and Protection
LOGIC
CONTROL
VREF
R2
ON
NTC
R1 = R2 ✕ (VREF / O.6 - 1)
R2 = VALUE OF THE NTC RESISTOR AT THE LIMIT TEMPERATURE
VREF = ANY REFERENCE VOLTAGE AVAILABLE OR VIN
0.6V
R1
MAX4271
MAX4272
MAX4273
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
20 ______________________________________________________________________________________
The ON and INC comparator inputs and the STAT and
OUTC can be pulled to voltages up to 14V indepen-
dently of VIN, thus allowing parts to be daisy-chained
and not be turned on through the internal protection
diodes. In some applications, it is useful to use connec-
tors with staggered leads. In Figure 14, the ON pin
forces the removable board to be powered up only
when all connections are made.
Auxiliary VCC
The auxiliary VCC is available on the MAX4273 and is
used to sustain the input voltage required for the device
to operate during a short-circuit condition on the board.
When a short occurs, the main system power supply
could collapse and the MAX4273 will not have enough
voltage to keep the gate drive operational and turn off
the external MOSFET. If the fault is not removed, the
system could remain in a sustained short-circuit state.
Connect a 1µF capacitor from the AUXVCC pin to GND.
This capacitor will deliver the necessary energy to the
gate drive until the MOSFET is turned off and the main
supply recovers. The 1µF capacitor is charged from VIN
through an internal switch during normal operation.
Maximum Load Capacitance
The MAX4271/MAX4272/MAX4273 can be used on the
backplane to regulate current upon insertion of a
removable card (Figure 16). This allows multiple cards
with different input capacitance to be inserted into the
same slot even if the card doesn’t have on-board hot-
swap protection.
The MAX4271/MAX4272/MAX4273 current-limiting fea-
ture is active during the startup period set by CTIM.
The startup period can be triggered if VIN is connected
to ON through a trace on the card. Once tSTART has
expired (timed out), the load capacitance has to be
charged or a fault condition is detected. To ensure
startup with a fixed CTIM, tSTART has to be longer than
the time required to charge the board capacitance. The
maximum load capacitance is calculated as follows:
CBOARD < tSTART ✕IFAST,SET / VIN
Input Transients
The voltage at VIN must be above the UVLO during
inrush and fault conditions. When a short condition
occurs on the board, the fault current can be higher
than the fast comparator current limit. The gate voltage
Figure 12. Power-On Reset
OUTC RESET
μP
INC
LLMON
IN SENSE GATE
VIN
MAX4273
Figure 14. Fail-Safe Connector
IN
ON
BACKPLANE
10k
1M
RESET
VCC
MAX4271
MAX4272
MAX4273
SENSE GATE
REMOVABLE
CARD
Figure 13. Power-On Reset and Temperature
GND LLMON
OUTC
ON
REF
IN
INC
SENSE GATE
NTC
VIN VOUT
MAX4273
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
______________________________________________________________________________________ 21
is discharged immediately, but note that the MOSFET is
not completely off until VGS < VTH. If the main system
power supply collapses below UVLO, the MAX4271/
MAX4272/MAX4273 will force the device to restart in
startup mode with a 150ms delay once the supply has
recovered. The main system power supply must be
able to deliver this fault current without excessive volt-
age drop.
The MOSFET is turned off in a very short time; there-
fore, the resulting dv/dt can be considerable. The back-
plane delivering the power to the external card must
have a fairly low inductance to limit the voltage tran-
sients caused by the removal of a fault. Bypassing the
input with a small capacitor alleviates false UVLO trips
due to these transients.
MOSFET Thermal Considerations
During normal operation, the MOSFET dissipates little
power, it is fully turned on, and its RDS(ON) is minimal.
The power dissipated in normal operation is PD=
ILOAD2x RDS(ON). A considerable amount of power is
dissipated during the startup and turn-off transients.
The design must take into consideration the worst-case
scenario of a continuous short-circuit fault present on
the board. Two cases need to be considered:
1) The single turn-on with the device latched after a
fault (when using MAX4271 or MAX4273 in latched
mode)
2) The continuous automatic retry (when using the
MAX4272 or MAX4273 in retry mode)
Use the following equation to calculate the maximum
transient thermal resistance (in °C/W) required for an
output short to ground:
ZθJA (max) = (TJMAX - TA) / (VIN ✕IFAST, SET)
MOSFET manufacturers typically include curves for the
transient thermal resistance, ZθJA, of the package
(Figure 17). Find the thermal impedance of the MOS-
FET by using tSTART as the pulse duration and by
choosing the single pulse curve for latched mode parts
or by choosing the duty cycle = 0.03 curve for the
MAX4272 (the duty cycle is fixed at 32:1). If the ZθJA
required is less than that of the package, reduce
tSTART, reduce IFAST,SET, use a heatsink on the MOS-
FET, or choose one with better thermal characteristics.
Figure 16. Using the MAX4271/MAX4272/MAX4273 on a
Backplane
IN
VIN
ON
BACKPLANE
MAX4271
MAX4272
MAX4273
SENSE GATE
CTIM
CBOARD
VOUT
REMOVABLE CARD
WITH NO HOT-INSERTION
PROTECTION
Figure 15. Adjustable Undervoltage Lockout and Output Voltage Reset Generator
OUTC RESET
μP
INC
LLMONON
IN SENSE GATE
VIN
MAX4273
•
•
•
•
•
•
100k
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
22 ______________________________________________________________________________________
For the MAX4273 in retry mode, the duty cycle can be
adjusted. Use the MOSFET ZθJA curve and the tSTART
pulse duration to choose a maximum duty cycle, D.
Calculate the retry time:
tRETRY = tSTART / D
Use Figure 8 to determine CTIM given tRETRY.
Design Procedure (MAX4273)
GIVEN:
• Hot-swap 5V supply to a 1000µF card
• MOSFET IRF7413A: RDS(on) = 0.0135Ω
• Operating current = 4A
• Overload current = 5A
• System current limit = 10A
• Retry enabled
PROCEDURE:
1) Select the current sense resistor:
Slow comparator threshold = 50mV
Overload current = 5A
Current-sense resistor value = 50mV/5A = 10mΩ
The device will initiate a slow fault if the load current
is greater than 5A for longer than 20µs after startup.
2) Set fast comparator threshold (RTH).
The MOSFET pulsed drain current limit is 58A.
Another consideration for setting the current limit is
the system requirement. Systems may glitch if 58A
load transients are present. For this example, the
load transient will be limited to 10A:
System current limit = 10A
Current-sense resistor = 10mΩ
Fast comparator threshold = 10mΩ✕10A = 100mV
Select RTH from Figure 7, RTH = 10kΩ
3) Set Startup timer.
Startup current = System current limit = 10A
VIN = 5V
CBOARD = 1000µF
tON = 1000µF ✕5V / 10A = 500µs
Give a factor of 2 guardband on the startup timer.
tSTART = 2 ✕tON = 1.0ms
From Figure 8, CTON = 3000pF.
4) Select Retry Timeout.
VIN = 5V.
IMAX = 10A.
Peak junction temperature, TJ= 150°CJ
Peak ambient temperature, TA= 85°CA
1001010.10.010.0010.0001
0.1
1
10
100
THERMAL RESPONSE (ZθJA)
t1, RECTANGULAR PULSE DURATION (s)
PDM
t1
t2
NOTES:
1. DUTY FACTOR D = t1 / t2
2. PEAK TJ = PDM X ZθJA + TA
D = 0.50
0.20
0.10
0.05
0.02
0.01
SINGLE PULSE
(THERMAL RESPONSE)
Figure 17. Example Curves (from IRF7413A) for Maximum Effective Transient Thermal Impedance, Junction to Ambient
Calculate the MOSFET thermal resistance required
for a short to ground.
ZθJA = (150°C - 85°C) / (5V ✕10A) = 1.30°C/W
Using tSTART = 1ms as the pulse duration, use
Figure 17 to select a duty cycle. The duty cycle
should be about 0.01 or less. This implies tRETRY =
tSTART / 0.01 = 100ms. From Figure 8, CTIM = 10nF.
Layout Considerations
To take full tracking advantage of the switch response
time to an output fault condition, it is important to keep
all traces as short as possible and to maximize the
high-current trace dimensions to reduce the effect of
undesirable parasitic inductance. Place the MAX4271/
MAX4272/MAX4273 close to the card’s connector. Use
a ground plane to minimize impedance and induc-
tance. Minimize the current-sense resistor trace length
(<10mm), and ensure accurate current sensing with
Kelvin connections (Figure 18).
When the output is short circuited, the voltage drop
across the external MOSFET becomes large. Hence,
the power dissipation across the switch increases, as
does the die temperature. An efficient way to achieve
good power dissipation on a surface-mount package is
to lay out two copper pads directly under the MOSFET
package on both sides of the board. Connect the two
pads to the ground plane through vias, and use
enlarged copper mounting pads on the top side of the
board.
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
______________________________________________________________________________________ 23
CTIM
CSPDGND
1
2
8
7
ON
STATSENSE
GATE
IN
SO
TOP VIEW
3
4
6
5
MAX4271
MAX4272
Pin Configurations
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
RTH OUTC
INC
REF
ON
STAT
CTIM
CSPD
CTON
MAX4273
QSOP/SO
AUXVCC
IN
CEXT
SENSE
GATE
LLMON
GND
Figure 18. Kelvin Connections for the Current-Sense Resistors
SENSE RESISTOR
HIGH-CURRENT PATH
MAX4271
MAX4272
MAX4273
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
24 ______________________________________________________________________________________
SOICN .EPS
PACKAGE OUTLINE, .150" SOIC
1
1
21-0041 B
REV.DOCUMENT CONTROL NO.APPROVAL
PROPRIETARY INFORMATION
TITLE:
TOP VIEW
FRONT VIEW
MAX
0.010
0.069
0.019
0.157
0.010
INCHES
0.150
0.007
E
C
DIM
0.014
0.004
B
A1
MIN
0.053A
0.19
3.80 4.00
0.25
MILLIMETERS
0.10
0.35
1.35
MIN
0.49
0.25
MAX
1.75
0.050
0.016L0.40 1.27
0.3940.386D
D
MINDIM
D
INCHES
MAX
9.80 10.00
MILLIMETERS
MIN MAX
16 AC
0.337 0.344 AB8.758.55 14
0.189 0.197 AA5.004.80 8
N MS012
N
SIDE VIEW
H 0.2440.228 5.80 6.20
e 0.050 BSC 1.27 BSC
C
HE
eBA1
A
D
0∞-8∞
L
1
VARIATIONS:
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
______________________________________________________________________________________ 25
QSOP.EPS
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
26 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 4/00 Initial release —
1 7/00 Removed future product designation for MAX4273 1
1a 4/01 Updated footer 1
2 12/07 Included Package codes in Ordering Information table, Updated Note 5 and
Package Outlines 1, 4, 24
