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MAX5976A/MAX5976B
2.7V to 18V, 7A, Hot-Swap Solution
General Description
The MAX5976A/MAX5976B are integrated solutions for
hot-swap applications requiring the safe insertion and
removal of circuit line cards from a live backplane. The
devices integrate a hot-swap controller, 24mI power
MOSFET, and electronic circuit-breaker protection in a
single package. The ICs are designed for protection of
2.7V to 18V supply voltages.
The devices provide inrush current control and short-
circuit detection during startup. During normal operation,
the devices provide circuit-breaker protection against
overload and short-circuit conditions. The circuit-breaker
function disconnects the power to the load if the load
current exceeds the circuit-breaker limit. The devices
are factory-calibrated to deliver accurate overcurrent
protection with Q10% accuracy. During a fault condi-
tion, the MAX5976A enters an autoretry mode while the
MAX5976B latches off. Both versions feature a resistor-
adjustable variable speed circuit-breaker threshold and
overtemperature protection. Additional features include
power-good and fault indicator outputs.
The ICs are available in a 16-pin, 5mm x 5mm, TQFN-
EP package and fully specified over the -40°C to +85°C
operating temperature range.
Applications
RAID Systems
Storage Bridge Bay
Disk Drive Power
Server I/O Cards
Industrial
Features
S 2.7V to 18V Operating Voltage Range
S 24mI Internal Power MOSFET
S 7A Load Current Capability
S No Sense Resistor Required
S ±10% Circuit-Breaker Threshold Accuracy
S Adjustable Circuit-Breaker Current
S Variable Speed Circuit-Breaker Response
S Thermal Protection
S Power-Good and Fault Outputs
S Latch-Off or Automatic Retry Options
S Drive-Present Signal Input
S Active-Low and Active-High Enables
19-5542; Rev 1; 4/11
Note: All devices are specified over the -40°C to +85°C
operating temperature range.
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
Ordering Information
Typical Application Circuit
EVALUATION KIT
AVAILABLE
R1
IN OUT
PRESDET
LOAD
(7A)
VPRESDET
ON1
CB
REG
R2
RCB
CREG
GND
2.7V TO 18V
2.7V TO 6V
CIN TVS
MAX5976A
MAX5976B
FAULT
PG
µP
ON2 RON2
RFAULT
RPG
VIN
REMOVABLE CARD
PART PIN PACKAGE FAULT
MANAGEMENT
MAX5976AETE+ 16 TQFN-EP* Autoretry
MAX5976BETE+ 16 TQFN-EP* Latched Off
MAX5976A/MAX5976B
2.7V to 18V, 7A, Hot-Swap Solution
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.
IN to GND ..............................................................-0.3V to +20V
CB to GND ..............................................-0.3V to (VREG + 0.3V)
ON1, REG to GND ..................................................-0.3V to +6V
OUT, ON2, PRESDET
to GND ............... -0.3V to the lower of (VIN + 0.3V) and +20V
PG, FAULT to GND ...............................................-0.3V to +26V
Continuous Power Dissipation (TA = +70NC)
TQFN (derate 33.3mW/NC above +70NC) (Note 1) ..2666.7mW
Operating Ambient Temperature Range ........... -40NC to +85NC
Maximum Junction Temperature .....................................+150NC
Storage Temperature Range ............................ -60NC to +150NC
Lead Temperature (soldering, 10s) ................................+300NC
Soldering Temperature (reflow) ......................................+260NC
ELECTRICAL CHARACTERISTICS
(VIN = 12V, VON1 = 2V, VON2 = VPRESDET = 0V, RCB = 40kI, TA = TJ = -40NC to +85NC, unless otherwise noted. Typical values are
at TA = +25NC.) (Note 3)
ABSOLUTE MAXIMUM RATINGS
Note 2: 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.
TQFN
Junction-to-Case Thermal Resistance (BJC) ...................30NC/W
Junction-to-Ambient Thermal Resistance (BJA) ............... ...2NC/W
PACKAGE THERMAL CHARACTERISTICS (Note 2)
Note 1: As per JEDEC51 standard (multilayer board).
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Input Supply Voltage Range VIN 2.7 18 V
Input Supply Current IIN VON1 = 3V, no load, 7A current-limit
threshold 5 7.5 mA
Default Undervoltage Lockout VUVLO VIN rising, VON1 = VIN 2.35 2.5 2.65 V
Default Undervoltage Lockout
Hysteresis VUVLO_HYS 0.1 V
ON1 Turn-On Threshold VON1_TH VON1 rising 1.17 1.21 1.25 V
ON1 Turn-On Threshold
Hysteresis VON1_HYS VON1 falling 0.1 V
ON1 Input Bias Current ION1 VON1 = 0 to 5V -1 +1 FA
CURRENT LIMIT
Circuit-Breaker Accuracy
(At Startup) ICB,TH
RCB = 40kI6.3 7 7.7
A
RCB = 28.57kI4.5 5 5.5
RCB = 20kI3.15 3.5 3.85
RCB = 10kI1.575 1.75 1.925
Slow-Comparator Response
Time (Note 4) tSCD 0.6% overcurrent 2.7 ms
30% overcurrent 200 Fs
MOSFET
Total On-Resistance RON 15 24 41 mI
LOGIC INPUTS (ON2, PRESDET)
Low Voltage Input VIL 2.7V < VIN < 18V 0.4 V
High Voltage Input VIH 2.7V < VIN < 18V 1.4 V
Input Current IIN VON2, VPRESDET = 0 to 6V -1 +1 FA
MAX5976A/MAX5976B
2.7V to 18V, 7A, Hot-Swap Solution
3
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 12V, VON1 = 2V, VON2 = VPRESDET = 0V, RCB = 40kI, TA = TJ = -40NC to +85NC, unless otherwise noted. Typical values are
at TA = +25NC.) (Note 3)
Note 3: All devices are 100% production tested at TA = +25°C. Limits over temperature are guaranteed by design.
Note 4: The current-limit slow-comparator response time is weighed against the amount of overcurrent so that the higher the over-
current condition, the faster the response time.
Typical Operating Characteristics
(VIN = 12V, VON1 = 2V, RCB = 40kω, VON2 = VPRESDET = 0V, TA = +25°C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
MAX5976 toc01
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
603510-15
4.5
5.0
5.5
6.0
4.0
-40 85
VON1 = 2V
VIN = 12V
VIN = 3V
VIN = 5V
CIRCUIT-BREAKER THRESHOLD
vs. CIRCUIT-BREAKER RESISTANCE
MAX5976 toc02
RCB (kI)
CIRCUIT-BREAKER THRESHOLD (A)
3530252015
2
4
6
8
10
0
10 40
VIN = 12V
CIRCUIT-BREAKER THRESHOLD
vs. TEMPERATURE
MAX5976 toc03
TEMPERATURE (°C)
CIRCUIT-BREAKER THRESHOLD (A)
603510-15
2
4
6
8
10
0
-40 85
VIN = 12V
RCB = 39.3kI
RCB = 30.1kI
RCB = 19.9kI
RCB = 10kI
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
OPEN-DRAIN OUTPUTS
FAULT, PG Output Low Voltage VOL Low-impedance state,
IFAULT = IPG = 5mA 0.4 V
FAULT, PG Output High
Leakage Current IOH High-impedance state,
VFAULT = VPG = 16V 1FA
OUT Bias Current IOUT VON1 = GND 10 FA
TIMING
Automatic Restart Delay After
Current-Limit Timeout tOFF 250 ms
PG Assertion Delay tPG From VOUT > VPG 16 ms
PG Threshold VPG VOUT = 12V 0.9 x
VIN V
THERMAL PROTECTION
Thermal-Shutdown Threshold 150 NC
Thermal-Shutdown Threshold
Hysteresis 20 NC
MAX5976A/MAX5976B
2.7V to 18V, 7A, Hot-Swap Solution
4
Typical Operating Characteristics (continued)
(VIN = 12V, VON1 = 2V, RCB = 40kω, VON2 = VPRESDET = 0V, TA = +25°C, unless otherwise noted.)
ON-RESISTANCE vs. TEMPERATURE
MAX5976 toc04
TEMPERATURE (°C)
ON-RESISTANCE (mI)
603510-15
25
30
35
40
20
-40 85
VIN = 12V
ILOAD = 100mA
TURN-ON WAVEFORM
MAX5976 toc05
VON1
2V/div
VOUT
10V/div
VPG
10V/div
ILOAD
5A/div
0A
0V
0V
0V
4ms/div
ILOAD = 5A
NORMAL TURN-OFF WAVEFORM
MAX5976 toc06
VON1
2V/div
VOUT
10V/div
VPG
10V/div
ILOAD
5A/div
0A
0V
0V
0V
4ms/div
ILOAD = 5A
FAULT SHUTDOWN WAVEFORM—OVERLOAD
(SLOW TRIP)
MAX5976 toc07
VOUT
10V/div
VFAULT
10V/div
VPG
10V/div
ILOAD
2A/div
0V
0V
0A
0V
2ms/div
FAULT SHUTDOWN WAVEFORM—SHORT
CIRCUIT
MAX5976 toc08
VOUT
10V/div
VFAULT
10V/div
VPG
10V/div
ILOAD
10A/div
0V
0V
0A
0V
4ms/div
ON1 RISING/FALLING THRESHOLD VOLTAGE
vs. TEMPERATURE
MAX5976 toc09
TEMPERATURE (°C)
VON1 RISING/FALLING THRESHOLD VOLTAGE
603510-15
1.12
1.14
1.16
1.18
1.20
1.22
1.24
1.10
-40 85
VON1 RISING
VON1 FALLING
PG ASSERTION DELAY
MAX5976 toc10
VON1
1V/div
VOUT
5V/div
VPG
5V/div
0V
0V
0V
4ms/div
AUTORETRY FUNCTIONALITY
MAX5976 toc11
VOUT
500mV/div
0V
0V
0V
40ms/div
ILOAD
2A/div
VFAULT
10V/div
ILOAD = 7A
CIRCUIT-BREAKER THRESHOLD TIME
vs. OVERCURRENT
MAX5976 toc12
OVERCURRENT (%)
CIRCUIT-BREAKER THRESHOLD TIME (ms)
2500200015001000500
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
0
0 3000
VIN = 12V
RCB = 19.9kI
MAX5976A/MAX5976B
2.7V to 18V, 7A, Hot-Swap Solution
5
Pin Description
Pin Configuration
PIN NAME FUNCTION
1 GND Ground
2–5 IN
Supply Voltage Input. IN is connected to the drain of the internal 24mI MOSFET. Bypass IN with
1FF capacitor to ground. Add a transient voltage suppressor diode from IN to GND for output
short-circuit protection.
6FAULT Fault Status Output. FAULT is an open-drain, active-low output. FAULT asserts low when an over-
current or overtemperature condition triggers a shutdown.
7 PG Power-Good Output. PG is an open-drain, active-high output. PG pulls low until the internal power
MOSFET is fully enhanced.
8–11 OUT Load Connection Point. Source of the internal power MOSFET.
12 PRESDET Active-Low Present-Detect Logic Input. Pulling PRESDET to GND enables the output if ON2 is low
and ON1 is high.
13 ON2 Active-Low Enable Logic Input. Pulling ON2 to GND enables the output if PRESDET is low and
ON1 is high.
14 CB Current-Limit Threshold Set. Connect a resistor from CB to GND to set the circuit-breaker threshold.
15 REG Internal Regulator Output. Bypass to ground with a 1FF capacitor. Do not power external circuitry
using the REG output.
16 ON1
Active-High Enable Comparator Input. Pulling ON1 high enables the output if PRESDET and
ON2 are held low. ON1 also sets the undervoltage threshold. See the Setting the Undervoltage
Threshold section.
— EP Exposed Pad. EP is internally grounded. Connect externally to ground plane for effective heat dis-
sipation. Do not use as the only ground connection.
15
16
14
13
6
5
7
IN
IN
GND
EP*
*CONNECT EP TO GND.
OUT
OUT
PRESDET
1 2
CB
4
12 11 9
REG
ON1
OUT
PG
FAULT
IN
MA5976A
MA5976B
IN OUT
3
10
ON2
TQFN
+
TOP VIEW
8
MAX5976A/MAX5976B
2.7V to 18V, 7A, Hot-Swap Solution
6
Functional Diagram
PRESDET
TEMP SENSE
2500X FAULT
PG
OUT
2X
15µA
1mA CB_COMP
SNS_OK
1V
ON2
REG CB GND
1.21V
UVLO
VREG
ON1
IN
SSET
CONTROL
LOGIC
CLR
R
Q
Q
LDO
O.9 X VIN
REFERENCE
GENERATOR
MAX5976A
MAX5976B
CHARGE PUMP
6µA
10µA
1.25V
MAX5976A/MAX5976B
2.7V to 18V, 7A, Hot-Swap Solution
7
Detailed Description
Enable Logic and
Undervoltage Lockout Threshold
The MAX5976A/MAX5976B enable the output as shown
in Table 1. The ICs turn on the output only when VON1
is high (VON1 > 1.21V) while ON2 and PRESDET are
low. The devices turn off the output when VON1 falls
below 1.21V - VHYS or whenever ON2 or PRESDET are
above VIH. A resistive divider from IN to ON1 and ground
provides the flexibility to set the undervoltage lockout
threshold to any desired level between VUVLO and 18V.
See Figure 1 and Setting the Undervoltage Threshold in
the Applications Information section.
Startup
Once the MAX5976A/MAX5976B output is enabled, the
device provides controlled application of power to a load.
The voltage at OUT will begin to rise at approximately
18kV/s until the programmed circuit-breaker current level
is reached, at which time the MAX5976A/MAX5976B will
actively limit inrush current at the circuit-breaker setting.
Because of this, the inrush current can be easily pro-
grammed by appropriate selection of RCB. This startup
mode of operation will continue for up to 16ms; after the
startup time elapses, the output will either have risen to
the IN potential, or if the device is still in current limit, it
will shut down and assert the FAULT output low.
The resulting dVOUT/dt during startup can be deter-
mined according to the following equation:
dVOUT/dt ≈ (ICB - ILOAD)/COUT
In this equation, ILOAD is any current drawn by a load
device during the output ramp time that does not charge
COUT. Make certain that RCB is chosen such that:
VIN x COUT/(ICB - ILOAD) < 16ms
This ensures that the output capacitance can be fully
charged before the 16ms startup timer elapses.
An open-drain power-good output goes high-impedance
16ms (typ) after the output has risen to more than 90% of
the input voltage to indicate a successful startup.
Charge Pump
An integrated charge pump provides the gate-drive volt-
age for the internal power MOSFET. The charge pump
generates +5V potential above VIN to fully enhance the
internal power MOSFET.
Circuit-Breaker Comparator
The current through the internal power MOSFET is com-
pared to a circuit-breaker threshold. An external resistor
between CB and ground sets this threshold.
The circuit-breaker comparator is designed so that the
load current can exceed the threshold for some amount
of time before tripping. The time delay varies inversely
with the overdrive above the threshold. The greater the
overcurrent condition, the faster the response time allow-
ing the devices to tolerate load transients and noise near
the circuit-breaker threshold.
The ICs also feature catastrophic short-circuit protec-
tion. During normal operation, if OUT is shorted directly
to ground, a fast protection circuit forces the gate of the
internal MOSFET to discharge quickly and disconnect
the output from the input.
Autoretry/Latch-Off
During a fault condition, the devices turn off the inter-
nal MOSFET disconnecting the output from the input.
The MAX5976A enters an autoretry mode with a fixed
250ms lockout time before reconnect can occur. The
MAX5676B latches off and remains off until the enable
logic is cycled off and on.
Figure 1. Undervoltage Threshold Setting
Table 1. Output Enable Truth Table
X = Don’t care.
VON1_TH = 1.21V (typ).
ON2
ON1
R1
R2
VIN
MAX5976A
MAX5976B
PRESDET
ACTIVE-
HIGH
ENABLE
1.21V
PRECISION
ANALOG INPUT
ON1
LOGIC INPUTS
OUT
ON2 PRESDET
VON1 > VON1_TH 0 0 ON
VON1 < (VON1_TH
- VON_HYS)X X OFF
X 1 X OFF
X X 1 OFF
MAX5976A/MAX5976B
2.7V to 18V, 7A, Hot-Swap Solution
8
Power-Good Delay
The devices feature an open-drain, power-good output
that asserts after 16ms (typ), indicating that OUT has
reached (0.9 x VIN) voltage.
REG
The devices include a linear regulator that outputs
2.6V at REG. REG provides power to the internal circuit
blocks of the ICs and must not be loaded externally. REG
requires a 1FF capacitor to ground for proper operation.
Fault Status Output (FAULT)
FAULT is an open-drain output that pulls low when a cur-
rent limit or an overtemperature fault shutdown occurs.
FAULT remains low until the next startup cycle. FAULT is
capable of sinking up to 5mA when asserted.
Thermal Protection
The devices enter a thermal shutdown mode in the event
of overheating caused by excessive power dissipation
or high ambient temperature. When the junction tem-
perature exceeds TJ = +150NC (typ), the internal thermal
protection circuitry turns off the internal power MOSFET.
The devices recover from thermal shutdown mode once
the junction temperature drops by 20NC (typ).
Applications Information
Setting the Undervoltage Threshold
The devices feature an independent ON/OFF control
(ON1) for the internal MOSFET. The devices operate
with a 2.7V to 18V input voltage range and has a default
2.5V (typ) undervoltage lockout threshold. The internal
MOSFET remains off as long as VIN < 2.5V and/or VON1
< VON1_TH. The undervoltage lockout threshold is pro-
grammable using a resistive divider between ON1 and
GND (Figure 1). When VIN is greater than 2.7V and VON1
exceeds the 1.21V (typ) threshold, the gate of the inter-
nal MOSFET enhances to 5V, with respect to VIN and the
devices' internal switch goes into normal operation. Use
the following equation to calculate the resistors values for
the desired undervoltage threshold:
IN
ON1_TH
V
R1 - 1 R2
V
= ×
where VIN is the desired turn-on voltage for the output
and VON1 is 1.21V. R1 and R2 create a resistive divider
from VIN to ON1. During normal operating conditions,
VON1 must remain above its 1.21V (typ) threshold. If
VON1 falls 100mV (VON1_HYS) below the threshold, the
internal MOSFET turns off, disconnecting the load from
the input.
Setting the Current Limit
An external resistor from CB to ground sets the current
limit for the devices. Use the following formula to set the
current limit:
LIMIT CB
0.175A
I (A) R ( )
1000
= × Ω
Ω
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.
Chip Information
PROCESS: BiCMOS
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
16 TQFN-EP T1655+3 21-0140 90-0073
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 9
© 2011 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
MAX5976A/MAX5976B
2.7V to 18V, 7A, Hot-Swap Solution
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 9/10 Initial release —
1 4/11 Added the Package Thermal Characteristics and Startup sections. 2, 7
