_______________________________________________________________ Maxim Integrated Products 1
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.
MAX5977A/MAX5977B
1V to 16V, Single-Channel, Hot-Swap Controllers
with Precision Current-Sensing Output
General Description
The MAX5977A/MAX5977B hot-swap controllers provide
complete protection for systems with a 1V to 16V single-
supply voltage.
During the initial insertion, the hot-swap controllers
limit the inrush current from damaging the board or
from shorting out the backplane. When the input volt-
age is above the undervoltage threshold and below the
overvoltage threshold, a 5FA current source powered
from the internal 5V charge pump drives the gate of an
external n-channel MOSFET, providing a slow turn-on
response. An internal current-sense amplifier in the IC
monitors the current across an external shunt resistor,
providing current sensing for wide input-sense voltage
range. The devices provide two levels of overcurrent
circuit-breaker protections: a fast-trip threshold for a fast
turn-off and a lower slow-trip threshold for a delayed
turn-off.
Exceeding either of the overcurrent circuit-breaker
thresholds forces the device into fault mode where the
external n-channel MOSFET is disabled. The MAX5977
is available in two versions that provide a latched-off
(MAX5977A) or autoretry (MAX5977B) output when the
device is in fault mode.
A calibration mode allows further calibration of the inte-
grated transconductance amplifier for production testing
of the final design. The devices are offered in a 20-pin,
4mm x 4mm, TQFN-EP package and are fully specified
from -40NC to +85NC.
Features
S 1% Accurate Current-Sense Amplifier Output
S Hot-Swap Monitors Operation from 1V to 16V
S Integrated Charge Pump Fully Enhances the
External n-Channel FET (VGATE = VIN + 5V)
S VariableSpeed/BiLevelK Fault Protection Provides
Electronic Circuit-Breaker Function
S Output Latched Off After Fault Condition
(MAX5977A)
S Autoretry After Fault Condition (MAX5977B)
S Power-Good Indicator
S Calibration Mode
S Small, 20-Pin, 4mm x 4mm TQFN-EP Package
Applications
Servers
Storage Systems
Network Switches and Routers
General Hot-Swap
19-5553; Rev 2; 7/11
Ordering Information
Typical Operating Circuit
VariableSpeed/BiLevel is a trademark of Maxim Integrated
Products, Inc.
Note: All devices are specified over the -40NC to +85NC oper-
ating temperature range.
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
EVALUATION KIT
AVAILABLE
MAX5977A
MAX5977B
CALSENSE SOURCE
CSOUT
FAULT
PG
CAL
PWR
AGND
SCOMP FCOMP IN SENSE GATE
GND
2.7V TO 16V
CALIBRATION
MODE INPUT
RCAL
RSCOMP RFCOMP
RSENSE
RGATE
+3.3V
RCSOUT
CGATE
CL
TO LOAD
CURRENT-SENSE
AMPLIFIER OUTPUT
FAULT OUTPUT
POWER-GOOD OUTPUT
VIN
1V TO 16V
PART PIN-PACKAGE FAULT RESPONSE
MAX5977AETP+ 20 TQFN-EP* Latched
MAX5977BETP+ 20 TQFN-EP* Autoretry
MAX5977A/MAX5977B
1V to 16V, Single-Channel, Hot-Swap Controllers
with Precision Current-Sensing Output
2
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.
PWR, SENSE, IN, FCOMP, SCOMP,
GATE, SOURCE, CALSENSE to GND ...............-0.3V to +28V
PG, CAL, BIAS, UV, OV, FAULT, CSOUT to GND ..-0.3V to +6V
REG to GND ............................................................-0.3V to +4V
GATE to SOURCE ...................................................-0.3V to +6V
IN to FCOMP, IN to SCOMP, IN to SENSE,
IN to CALSENSE ..................................................-0.3V to +1V
GND to AGND ......................................................-0.3V to +0.3V
FAULT, PG Current ........................................... -1mA to +50mA
GATE, SOURCE, GND Current ........................................750mA
Input/Output Current (all other pins) ..................................20mA
Continuous Power Dissipation (TA = +70NC)
20-Pin TQFN, Single-Layer Board
(derate 16.9mW/NC above +70NC)..........................1355.9mW
20-Pin TQFN, Multilayer Board
(derate 25.6mW/NC above +70NC)..........................2051.3mW
Junction-to-Ambient Thermal Resistance (Note 1)
BJA, Single-Layer Board ........................................... +59NC/W
BJA, Multilayer Board ................................................ +39NC/W
Junction-to-Case Thermal Resistance (Note 1)
BJC, Single-Layer and Multilayer Board...................... +6NC/W
Operating Temperature Range .......................... -40NC to +85NC
Junction Temperature .....................................................+150NC
Storage Temperature Range ............................ -65NC to +150NC
Lead Temperature (soldering, 10s) ................................+300NC
Soldering Temperature (reflow) ......................................+260NC
ABSOLUTE MAXIMUM RATINGS
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-
layer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial.
ELECTRICAL CHARACTERISTICS
(VPWR = VIN = 12V, RSENSE = 4mI, RFCOMP = RSCOMP = 2kI, RGATE = 1kI, CGATE = 330nF, CREG = 1FF, unless otherwise noted.
Typical Values at VPWR = VIN = 3.3V, TA = +25NC, unless otherwise noted.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Operating Voltage Range VPWR 2.7 3.3 16 V
Undervoltage Lockout VUVLO Minimum rising voltage on PWR 2.69 V
Undervoltage-Lockout Hysteresis VUVLOHYS 100 mV
Supply Current IPWR 0.734 4 mA
Internal LDO Output Voltage VREG 2.7V < VPWR < 16V, 0 to 1mA 2.49 2.6 V
CURRENT-MONITORING FUNCTION
IN Input Range Common-mode range 1 16 V
SCOMP Input Range 1 16 V
FCOMP Input Range 1 16 V
IN Input Current 135 FA
SENSE Input Current VIN = VSENSE = 1V to 16V 6 FA
Circuit-Breaker Current (Slow
Comparator) ISCOMP VSCOMP = 1V to 16V 24.0 25 26.0 FA
Circuit-Breaker Current (Fast
Comparator) IFCOMP VFCOMP = 1V to 16V 48.1 50 51.4 FA
Slow Current-Limit Threshold
Error VSENSE - VSCOMP = 50mV -2.0 +2.1 mV
Fast Current-Limit Threshold Error VSENSE - VFCOMP = 100mV -2.2 +1.4 mV
Slow-Comparator Response Time tSCD 1mV overdrive 1 ms
50mV overdrive 130 Fs
Fast-Comparator Response Time tFSD 10mV overdrive, from overload condition,
VPWR = 12V 200 ns
MAX5977A/MAX5977B
1V to 16V, Single-Channel, Hot-Swap Controllers
with Precision Current-Sensing Output
3
ELECTRICAL CHARACTERISTICS (continued)
(VPWR = VIN = 12V, RSENSE = 4mI, RFCOMP = RSCOMP = 2kI, RGATE = 1kI, CGATE = 330nF, CREG = 1FF, unless otherwise noted.
Typical Values at VPWR = VIN = 3.3V, TA = +25NC, unless otherwise noted.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
CURRENT-SENSE AMPLIFIER
Input Common-Mode Range VIN - VSENSE 1.5 V
Input Offset Error 0.1 mV
Transconductance Gain gM
10mV P (VIN - VSENSE) P 50mV,
-40NC P TA P +85NC2457 2500 2537
FS
10mV P (VIN - VSENSE) P 50mV,
0NC P TA P +25NC2467 2500 2532
Combined Gain and Offset
Accuracy
Set VIN - VSENSE = 50mV, measure ICSOUT,
VCSOUT = 25mV (-40NC P TA P +85NC) 122.1 125 128
FA
Set VIN - VSENSE = 50mV, measure ICSOUT,
VCSOUT = 25mV (0N P TA P +25NC) 123.5 125 126.5
Set VIN - VSENSE = 10mV, measure ICSOUT,
VCSOUT = 25mV (-40NC P TA P +85NC) 22.5 25 27.6
Set VIN - VSENSE = 10mV, measure ICSOUT,
VCSOUT = 25mV (0N P TA P +25NC) 24.0 25 26.0
Total Full-Scale Error
2mV < (VIN - VSENSE) < 10mV
(-40NC P TA P +85NC),
% error = (ICSOUT - (VIN - VSENSE) x
0.0025)/(10mV x 0.0025)
-10 +10 % of
10mV
Full-Scale
Output
2mV < (VIN - VSENSE) < 10mV
(0NC P TA P +25NC),
% error = (ICSOUT - (VIN - VSENSE) x
0.0025)/(10mV x 0.0025)
-4.21 +4.21
2mV < (VIN - VSENSE) < 25mV
(-40NC P TA P +85NC),
% error = (ICSOUT - (VIN - VSENSE) x
0.0025)/(25mV x 0.0025)
-4.1 +4.1 % of
25mV
Full-Scale
Output
2mV < (VIN - VSENSE) < 25mV
(0NC P TA P +25NC),
% error = (ICSOUT - (VIN - VSENSE) x
0.0025)/(25mV x 0.0025)
-1.68 +1.68
2mV < (VIN - VSENSE) < 50mV
(-40NC P TA P +85NC),
% error = (ICSOUT - (VIN - VSENSE) x
0.0025)/(50mV x 0.0025)
-2.34 +2.3 % of
50mV
Full-Scale
Output
2mV < (VIN - VSENSE) < 50mV
(0NC P TA P +25NC),
% error = (ICSOUT - (VIN - VSENSE) x
0.0025)/(50mV x 0.0025)
-1.18 +0.9
Output Common-Mode Range CSOUT voltage range 0 2.5 V
POWER-GOOD
PG Delay tdPG 50 ms
PG Threshold Rising VTHRPG VIN - VSOURCE falling 100 mV
PG Threshold Hysteresis 100 mV
MAX5977A/MAX5977B
1V to 16V, Single-Channel, Hot-Swap Controllers
with Precision Current-Sensing Output
4
ELECTRICAL CHARACTERISTICS (continued)
(VPWR = VIN = 12V, RSENSE = 4mI, RFCOMP = RSCOMP = 2kI, RGATE = 1kI, CGATE = 330nF, CREG = 1FF, unless otherwise noted.
Typical Values at VPWR = VIN = 3.3V, TA = +25NC, unless otherwise noted.) (Note 2)
Note 2: All devices 100% tested at TA = +25°C. Limits over temperature guaranteed by design.
Typical Operating Characteristics
(VPWR = VIN = 3.3V, TA = +25NC, RFCOMP = RSCOMP = 2kI, RGATE = 1kI, CGATE = 330nF, CREG = 1FF, unless otherwise noted.)
IPWR vs. VPWR
MAX5977 toc01
VPWR (V)
IPWR (mA)
15105
0.64
0.65
0.66
0.67
0.68
0.69
0.70
0.71
0.72
0.73
0.63
0 20
VIN - VSENSE vs. ICSOUT
VIN - VSENSE (mV)
ICSOUT (µA)
40302010
25
50
75
100
125
0
0 50
MAX5977 toc02
VIN = VPWR = 12V
RCSOUT = 10kI
TRANSCONDUCTANCE
vs. TEMPERATURE
MAX5977 toc03
TEMPERATURE (°C)
Gm (µS)
7550250-25
2460
2470
2480
2490
2500
2510
2520
2530
2540
2550
2450
-50 100
VIN = VPWR = 12V
VIN - VSENSE = 10mV AND 50mV
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
CHARGE PUMP (GATE)
Charge-Pump Output Voltage VOHGATE Relative to VSOURCE 4.5 5 5.5 V
Charge-Pump Output Source
Current IGATEPU VGATE = VSOURCE = 0V 4 5 6 FA
VIN - VSOURCE < 100mV 8 10 12
Charge-Pump Pulldown Current IGATEPD VGATE = 2V, VSOURCE = 0 to 16V 500 mA
OUTPUTS (FAULT, PG)
Output Voltage Low VOLFAULT/
VOLPG ISINK = 3.2mA 0.4 V
Output Leakage (Open Drain) ILKFAULT/
ILKPG Tested at 0V and 5.2V 1 FA
UV/OV COMPARATOR INPUTS
UV/OV Threshold VUV/OVR UV, OV rising input voltage threshold 580 590 600 mV
UV/OV Threshold Hysteresis VUV/OVHYS UV, OV falling input hysteresis 4 %
UV/OV Input Current ILKUV/
ILKOV VUV = VOV = 0V and 5.5V -100 +100 nA
CALIBRATION MODE
CAL Low-Voltage Input VILCAL 0.4 V
CAL High-Voltage Input VIHCAL 1.4 V
CAL Input Current IIHCAL VCAL = 2.5V, the CAL input pulls low if left
unconnected 20 FA
CALSENSE Input Current ±300 FA
FAULT RESPONSE
Retry Timeout Period tRETRY MAX5977B 175 ms
MAX5977A/MAX5977B
1V to 16V, Single-Channel, Hot-Swap Controllers
with Precision Current-Sensing Output
5
Typical Operating Characteristics (continued)
(VPWR = VIN = 3.3V, TA = +25NC, RFCOMP = RSCOMP = 2kI, RGATE = 1kI, CGATE = 330nF, CREG = 1FF, unless otherwise noted.)
SLOW-COMPARATOR RESPONSE TIME
(50mV OVERDRIVE)
MAX5997 toc08
VIN - VSENSE
50mV/div
VGATE
5V/div
VSOURCE
2V/div
0V
0V
0V
100µs/div
RSENSE = 4mI
CURRENT OUTPUT ERROR (%)
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1.0
-1.0
CURRENT OUTPUT ERROR
vs. VIN - VSENSE
MAX5977 toc06
VIN - VSENSE (mV)
10 20 30 400 50
VIN = VPWR = 12V
RCSOUT = 10kI
I_COMP vs. TEMPERATURE
MAX5977 toc04
I_COMP (µA)
5
10
15
20
25
30
35
40
45
50
55
0
TEMPERATURE (°C)
7550250-25-50 100
IFCOMP
ISCOMP
SLOW-COMPARATOR RESPONSE TIME
(50mV OVERDRIVE)
MAX5977 toc09
VIN - VSENSE
100mV/div
VGATE
5V/div
VSOURCE
2V/div
0V
0V
0V
20µs/div
RSENSE = 4mI
tSCD vs. OVERDRIVE VOLTAGE
MAX5977 toc07
OVERDRIVE VOLTAGE (mV)
tSCD (µs)
45403530252015105
1000
100
0 50
VGATE vs. VIN
MAX5977 toc05
VIN (V)
VGATE (V)
15105
4.80
4.85
4.90
4.95
5.00
5.05
5.10
5.15
5.20
5.25
4.75
0 20
MAX5977A/MAX5977B
1V to 16V, Single-Channel, Hot-Swap Controllers
with Precision Current-Sensing Output
6
Typical Operating Characteristics (continued)
(VPWR = VIN = 3.3V, TA = +25NC, RFCOMP = RSCOMP = 2kI, RGATE = 1kI, CGATE = 330nF, CREG = 1FF, unless otherwise noted.)
ICSOUT SMALL-SIGNAL
PULSE RESPONSE
MAX5977 toc12
VIN - VSENSE
5mV/div
VCSOUT
100mV/div
0V
0V
20µs/div
RCSOUT = 10kI
ICSOUT LARGE-SIGNAL
PULSE RESPONSE
MAX5977 toc13
VIN - VSENSE
20mV/div
VCSOUT
500mV/div
0V
0V
20µs/div
RCSOUT = 10kI
FAST-COMPARATOR RESPONSE TIME
(10mV OVERDRIVE)
MAX5977 toc10
VIN - VSENSE
100mV/div
VGATE
5V/div
VSOURCE
2V/div
0V
0V
0V
2µs/div
RSENSE = 4mI
tFSD
VFCOMP
FAULT RETRY TIME
(MAX5977B ONLY)
MAX5977 toc11
VIN - VSENSE
50mV/div
VGATE
5V/div
VSOURCE
2V/div
0V
0V
0V
40ms/div
RSENSE = 4mI
MAX5977A/MAX5977B
1V to 16V, Single-Channel, Hot-Swap Controllers
with Precision Current-Sensing Output
7
Pin Description
Pin Configuration
19
20
18
17
7
6
8
PWR
OV
9
REG
GATE
CSOUT
PG
SOURCE
1
EP*
*CONNECT TO AGND.
2
I.C.
4 5
15 14 12 11
I.C.
BIAS
SENSE
IN
SCOMP
FCOMP
MAX5977A
MAX5977B
AGND GND
3
13
CAL
16 10 CALSENSE
FAULT
THIN QFN
TOP VIEW
UV
PIN NAME FUNCTION
1 REG Regulator Output. Bypass REG with a 1FF capacitor.
2 PWR Power-Supply Input. Bypass PWR with a 0.1FF or higher value capacitor.
3 AGND Analog Ground
4 UV Active-High Precision Turn-On Input. UV is used to turn on/off the output and set the input
undervoltage lockout threshold.
5 OV Active-Low Precision Turn-On Input. OV is used to turn on/off the output and set the input overvoltage
lockout threshold.
6 FCOMP Fast Circuit-Breaker Comparator Input. Connect FCOMP to IN with a resistor to set the fast-trip circuit-
breaker threshold.
7 SCOMP Slow Circuit-Breaker Comparator Input. Connect SCOMP to IN with a resistor to set the slow-trip
circuit-breaker threshold.
8 IN Hot-Swap Voltage-Monitoring Input
9 SENSE Current-Sense Voltage Input. The voltage across an external sense resistor between IN and SENSE is
used to measure the channel current.
10 CALSENSE Calibration Voltage Input
11 PG Power-Good, Active-High Open-Drain Output
12 CSOUT Transconductance Current-Sense Amplifier Output. The output current of CSOUT is the product of the
voltage measured between SENSE and IN and the transconductance gain (2500FS typ).
13 GND Ground
14 GATE Gate-Driver Output. Connect GATE to the gate of the external n-channel MOSFET switch.
15 SOURCE MOSFET Source Voltage Input. Connect SOURCE to the source of the external n-channel MOSFET.
16 FAULT Active-Low, Open-Drain Fault Output. When an overcurrent occurs, FAULT goes low.
17 CAL Calibration Mode Select Input
18, 19 I.C. Internally Connected. Connect to ground.
20 BIAS Bias Input. Connect BIAS to REG.
— EP Exposed Pad. Connect to AGND.
MAX5977A/MAX5977B
1V to 16V, Single-Channel, Hot-Swap Controllers
with Precision Current-Sensing Output
8
Functional Diagram
MUX
25µA
SLOW CB
50µA
CS AMPLIFIER
OVERDRIVE
DELAY 5µA
10µA 10µA
CSOUT
GATE
SOURCE
PG
FAULT
GND
AGND
IN
SENSE
CALSENSE
CAL
SCOMP
FCOMP
UV
OV
PWR
REG
BIAS
50ms
PG TIMER
S
1
0
MAX5977A
MAX5977B
OD DELAY/
CB TIMER
2MHz
OSCILLATOR
IN
IN - 100mV
GATE
PULLDOWN
CHARGE
PUMP
FAST CB
OVP
POR
S
R
AUTORETRY ENABLE
MAX5977B
ONLY
0.6V
0.59V
0.59V
REF/
BIAS
LDO
UVLO
UVP
RETRY TIMER
Q
MAX5977A/MAX5977B
1V to 16V, Single-Channel, Hot-Swap Controllers
with Precision Current-Sensing Output
9
Detailed Description
The hot-swap controllers provide electronic circuit-
breaker protection and precision current sensing for a
single-supply voltage from 1V to 16V. Programmable
undervoltage and overvoltage protection qualifies the
supply voltage prior to enhancing the external n-channel
MOSFET with the internal gate driver.
The VariableSpeed/BiLevel fault levels are program-
mable with external resistors providing both slow and
fast circuit-breaker protection. The transconductance
current-sense amplifier provides continuous current
monitoring with high accuracy and features a calibration
mode for production testing.
Programmable Undervoltage
and Overvoltage Protection
The programmable undervoltage and overvoltage pro-
tection enables the hot-swap channel when the voltage
at UV is above 590mV, and the voltage at OV is below
590mV. After the hot-swap channel is enabled, the hot-
swap channel is disabled if the voltage at OV exceeds
the 590mV threshold.
Gate Driver
An integrated 5V charge pump supplies the gate-driver
output of the devices, allowing it to fully enhance the
external n-channel MOSFET during normal operation.
The 5FA (typ) current source at GATE slowly charges the
gate-to-source capacitance of the external n-channel
MOSFET to 5V (typ) relative to the SOURCE input.
Programmable Fast-Trip and Slow-Trip
Overcurrent Circuit Breaker
During normal operation with the channel turned on, two
analog comparators are used to detect an overcurrent
condition by comparing the voltage across the external
sense resistor (RSENSE) connected between IN and
SENSE to the voltages across the respective external
overcurrent circuit-breaker threshold set resistors con-
nected from IN to FCOMP and SCOMP. Precision cur-
rent sources at the FCOMP and SCOMP inputs establish
these thresholds.
If the voltage across the sense resistor is less than
the fast-trip and slow-trip overcurrent circuit-breaker
thresholds, the GATE output remains high. If either of
the thresholds is exceeded due to an overcurrent condi-
tion, the GATE output is pulled down to SOURCE by a
500mA current sink, and the FAULT and PG outputs are
asserted low.
If the sense voltage rises above the fast circuit-breaker
threshold, the devices turn off the external MOSFET in
200ns (typ).
If the sense voltage rises above the slow circuit-breaker
threshold, the internal timer begins counting. If the sense
voltage remains above the slow circuit-breaker threshold
until the timer expires, the devices turn off the external
MOSFET. The slow circuit-breaker timer occurs in 1ms
(typ) when the slow-current comparator threshold is over-
driven by 1mV and 130Fs (typ) when overdriven by 50mV.
Current-Sense Amplifier
The integrated transconductance current-sense ampli-
fier features high accuracy with less than 1% error over
its 10mV to 50mV input range, and provides continu-
ous current monitoring into the load. The sense voltage
of the external sense resistor connected between IN
and SENSE is multiplied by the transconductance gain
(2500FS typ) of the amplifier with the resulting current
output at CSOUT.
Calibration Mode
The devices' calibration mode bypasses the trans-
conductance amplifier inputs to measure the voltage
between IN and CALSENSE when the calibration mode
select input CAL is high.
This enables the user to apply a known calibration
voltage across the current-sense amplifier input. This
voltage corresponds to a full scale for the actual sense
voltage. During the calibration mode, the current-sense
amplifier only measures the calibration voltage between
IN and CALSENSE.
The calibration mode is completely asynchronous and
does not disrupt the circuit-breaker threshold compari-
son. Once in calibration mode there is no expiration until
the CAL input is brought low. This allows the calibration
to occur at multiple voltages by applying various calibra-
tion voltages during the calibration mode.
Fault Output
The FAULT output goes low when a slow or fast com-
parator current-limit fault has occurred.
On the MAX5977A, the device is latched in fault mode
until it is reset either by initiating a full power-on reset or
pulling UV below 590mV.
On the MAX5977B, the device reenables the hot-swap
output after the autoretry timer has expired in 175ms
and FAULT is pulled high if the fault condition has been
removed and startup conditions are met.
MAX5977A/MAX5977B
1V to 16V, Single-Channel, Hot-Swap Controllers
with Precision Current-Sensing Output
10
Power-Good Output
The open-drain, active-high output PG indicates the
power-good status of the output. Once the input voltage
satisfies the undervoltage and overvoltage requirements
for startup and VIN - VSOURCE is less than 100mV and
the VGATE - VSOURCE > 4V, the PG timer is started. At
the expiration of the 50ms PG timer, PG is asserted high.
Applications Information
Undervoltage and Overvoltage Protection
The undervoltage and overvoltage protection is pro-
grammed with a voltage-divider formed by three resis-
tors (R1, R2, and R3) placed in series. The resistor
values should be selected such that the series current,
IS, is greater than 5FA. The resistor values are then cal-
culated using the following equations with the overvolt-
age threshold (VOVR), undervoltage threshold (VUVR),
and the overvoltage hysteresis (VOVHYS) obtained from
the Electrical Characteristics table:
( )
( )
OVR
S
IN,OV UVR
IN,UV OVR OVHYS
IN,UV
UVR
V
R3 I
V V
R2 1 R3
V V V
V
R1 1 R2 R3
V
−
−
=
×
= ×
×
= − × +
where VIN,UV and VIN,OV are the desired undervoltage
and overvoltage thresholds for the hot-swap input volt-
age IN.
Programmable Slow and Fast Current Limit
The slow and fast current-limit thresholds are pro-
grammed by connecting resistors between the high
side of RSENSE to SCOMP and FCOMP. The current-limit
thresholds are set using the following equations:
SENSE, SCOMP SENSE
SCOMP
I R
R25 A
×
=µ
and:
SENSE, FCOMP SENSE
FCOMP
I R
R50 A
×
=µ
where ISENSE,_COMP is the desired circuit-breaker cur-
rent limit for the slow or fast current limit.
Startup Sequence
When all conditions for channel turn-on are met, the
external n-channel MOSFET switch is fully enhanced
with a typical gate-to-source voltage of 5V to ensure
a low drain-to-source resistance. The charge pump at
GATE sources 5FA to control the output voltage turn-on
voltage slew rate. An external capacitor must be added
from GATE to ground to further reduce the voltage slew
rate. Placing a 1kI resistor in series with this capaci-
tance prevents the added capacitance from increasing
the gate turn-off time. Total inrush current is the load cur-
rent summed with the product of the gate voltage slew
rate dV/dt and the load capacitance.
To determine the output dV/dt during startup, divide the
GATE pullup current IGATEPU by the GATE to ground
capacitance. The voltage at the source of the external
MOSFET follows the gate voltage, so the load dV/dt is
the same as the gate dV/dt. Inrush current is the product
of the dV/dt and the load capacitance. The time to start
up tSU is the hot-swap voltage VIN divided by the output
dV/dt.
Be sure to choose an external MOSFET that can handle
the power dissipated during startup. The inrush cur-
rent is roughly constant during startup and the voltage
drop across the MOSFET (drain to source) decreases
linearly as the load capacitance charges. The resulting
power dissipation is therefore roughly equivalent to a
single pulse of magnitude (VIN x Inrush current)/2 and
duration tSU. Refer to the thermal resistance charts in
the MOSFET data sheet to determine the junction tem-
perature rise during startup, and ensure that this does
not exceed the maximum junction temperature for worst-
case ambient conditions.
Transconductance Current-Sense Amplifier
The current-sense resistor, RSENSE, must be connected
between IN and SENSE to sense the average current
into the load. The voltage drop across RSENSE should
be less than or equal to the slow current-limit threshold;
therefore, RSENSE should be selected based on the fol-
lowing equation:
SENSE SENSE,FS SCOMP
R I V× ≤
where ISENSE,FS is the full-scale current into the load
and VSCOMP is the slow current-limit threshold. A Kelvin
sense connection should be used to connect RSENSE to
IN and SENSE.
MAX5977A/MAX5977B
1V to 16V, Single-Channel, Hot-Swap Controllers
with Precision Current-Sensing Output
11
An output resistor, RCSOUT, must be connected between
the transconductance current-sense amplifier output
CSOUT and AGND. The transconductance GM, of the
amplifier is typically 2500FS:
CSOUT M SENSE, FS
R G V 2.5V× × ≤
n-Channel MOSFET Selection
Select the external n-channel MOSFET according to the
application’s current level. The MOSFET’s on-resistance
(RDS(ON)) should be chosen low enough to have a mini-
mum voltage drop at full load to limit the MOSFET power
dissipation. High RDS(ON) causes output ripple if there
is a pulsating load. Determine the device power rating to
accommodate a short-circuit condition on the board at
startup and when the device is in automatic-retry mode
(see the MOSFET Thermal Considerations section).
The MAX5977A’s fault latch allows the use of MOSFETs
with lower power ratings. A MOSFET typically withstands
single-shot pulses with higher dissipation than the speci-
fied package rating.
MOSFET Thermal Considerations
During normal operation, the external MOSFETs dis-
sipate little power. The MOSFET RDS(ON) is low when
the MOSFET is fully enhanced. The power dissipated in
normal operation is PD = ILOAD2 x RDS(ON). The most
power dissipation occurs during the turn-on and turn-off
transients when the MOSFETs are in their linear regions.
Take into consideration the worst-case scenario of a
continuous short-circuit fault; consider these two cases:
1) The single turn-on with the device latched after a fault
(MAX5977A).
2) The continuous automatic retry after a fault
(MAX5977B).
MOSFET manufacturers typically include the package
thermal resistance from junction to ambient (RBJA) and
thermal resistance from junction to case (RBJC), which
determine the startup time and the retry duty cycle
(d = tSU/(tSU + tRETRY)). Calculate the required transient
thermal resistance with the following equation:
JMAX A
JA(MAX) IN INRUSH
T T
ZV I
θ×
≤×
Layout Considerations
To take full 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 resistance and inductance. Place the devices
close to the card’s connector, and a 0.01FF capacitor to
GND should be placed as close as possible to VIN. Use
a ground plane to minimize impedance and inductance.
Minimize the current-sense resistor trace length and
ensure accurate current sensing with Kelvin connec-
tions.
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 pack-
age 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.
Related Parts
PART DESCRIPTION
MAX5970
0 to 16V, Dual Hot-Swap Controller with
a 10-Bit Current and Voltage Monitor and
Four LED Drivers
MAX5978
0 to 16V, Single Hot-Swap Controller with
a 10-Bit Current and Voltage Monitor Plus
Four LED Drivers
MAX5977A/MAX5977B
1V to 16V, Single-Channel, Hot-Swap Controllers
with Precision Current-Sensing Output
12
Typical Application Circuit
Chip Information
PROCESS: BiCMOS
Package Information
For the latest package outline information and land patterns,
go to www.maxim-ic.com/packages. Note that a “+”, “#”, or
“-” in the package code indicates RoHS status only. Package
drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND PATTERN
NO.
20 TQFN-EP T2044+3 21-0139 90-0037
MAX5977A
MAX5977B
UV SOURCE
CSOUT
FAULT
PG
CAL
OV
CALSENSE
PWR
BIAS
REG AGND
SCOMP FCOMP
125µA
PRECISION
CURRENT
SOURCE
MAX6033AAUT25
IN SENSE GATE
GND
2.7V TO 16V
*OPTIONAL
RSCOMP RFCOMP
RSENSE
RGATE
+3.3V
RCSOUT
MAX1393
ADC
CGATE
CL
TO LOAD
I/O
I/O
I/O
µP
VIN
1V TO 16V
49.9IR2
R3
R1
OUTF
0.1µF
5.1kI4.99kI
10kI10kI
1µF
1µF
0.1µF
OUTS
GND
IN
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 13
© 2011 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
MAX5977A/MAX5977B
1V to 16V, Single-Channel, Hot-Swap Controllers
with Precision Current-Sensing Output
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 9/10 Initial release —
1 1/11 Changed current-sense amplifier specifications in Electrical Characteristics table 3
2 7/11 Updated Electrical Characteristics specifications to reflect improved yield of part 2, 3
