19-1694; Rev 2; 12/07
KIT
ATION
EVALU
E
L
B
A
IL
AVA
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
Features
The MAX4271/MAX4272/MAX4273 comprise a complete family of integrated 3V to 12V hot-swap controllers. They allow the safe insertion and removal of
circuit cards into live backplanes.
The discharged filter capacitors of the circuit card provide a low impedance to the live backplane. High inrush currents from the backplane to the circuit card can
burn up connectors and components, or momentarily
collapse the backplane power supply leading to a system 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 programmed (MAX4273) methods.
The MAX4271 family includes many integrated features
that reduce component count and design time. An onboard charge pump provides the gate drive for a lowcost, 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 condition, 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 during board removal.
♦ 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
DualSpeed/BiLevel is a trademark of Maxim Integrated
Products.
Pin Configurations appear at end of data sheet.
________________________Applications
Base Stations
RAID
Remote-Access Servers
Network Routers and
Switches
ISDN
Ordering Information
PART
TEMP RANGE
PINPACKAGE
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
Typical Operating Circuit
BACKPLANE
VCC
REMOVABLE CARD
M1
N
RSENSE
2.7V TO 13.2V
VOUT
CBOARD
IN
STAT
GND
ON
SENSE
GATE
STAT
CSPD
ON
MAX4271
MAX4272
CTIM
GND
CTIM
________________________________________________________________ Maxim Integrated Products
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.
1
MAX4271/MAX4272/MAX4273
General Description
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
ABSOLUTE MAXIMUM RATINGS
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
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)
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.
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.
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)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
POWER SUPPLIES
Input Voltage Range
VIN
Supply Current
IQ
2.7
VON = VIN
0.6
13.2
V
1
mA
CURRENT CONTROL
Slow Comparator Threshold
VSC,TH
Slow Comparator Response
Time
tCSPD
Fast Comparator Threshold
VFC,TH
TA = +25°C
VIN - VSENSE
TA = TMIN to TMAX
SENSE Input Bias Current
IB,SENSE
55
56
mV
10
20
40
μs
CSPD = 100nF to GND
10
20
40
ms
45
50
55
MAX4273
only
5kΩ on
RTH to
VIN
TA = +25°C
TA = TMIN to TMAX
43.5
75kΩ
on RTH
to VIN
TA = +25°C
675
TA = TMIN to TMAX
650
RTH = GND
tFCD
50
CSPD = floating
MAX4271/MAX4272
Fast Comparator Response
Time
45
43.5
180
56
750
825
mV
840
200
220
10mV overdrive, from overload condition to
gate discharging
350
VSENSE = VIN
0.2
10
ns
μA
MOSFET DRIVER
Startup Period
(Notes 4, 5)
tSTART
Gate Charge Current
IGATE
2
MAX4271/MAX4272 CTIM = 100nF
21
31
41
MAX4273 CTON = 100nF
21
31
41
ms
No capacitor
5.5
μs
GATE = IN (Note 6)
100
μA
_______________________________________________________________________________________
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
(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
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
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
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
Minimum Gate Drive Voltage
Measured with
respect to VIN,
IGATE = 8.5µA
VIN ≥ 5V
MAX
60
µs
μs
7.5
V
VIN ≥ 2.7V
2.7
0.4
1
2.75
During startup (current regulation provided
by fast comparator)
25
70
195
During normal discharge, due to a slow
comparator fault in normal mode, or by ON
going low
75
200
550
LLMON Overvoltage Threshold
Startup is initiated only after VLLMON is less
than this voltage (MAX4273)
0.1
GATE Overvoltage Threshold
Startup is initiated only after VGATE is less
than this voltage
0.1
LLMON Impedance
Impedance to GND, after a fault (MAX4273)
IGATE,DIS
V
5
During fast discharge, due to a fast
comparator fault in normal operation
Gate Discharge Current
UNITS
mA
μA
V
0.6
1
V
kΩ
REFERENCE (MAX4273)
Output Voltage
VREF
ΔVREF,
Load Regulation
LOAD
ON AND RESET COMPARATORS
Threshold Voltage
1.164
IREF = 0 to 100μA, VIN = 5V
VIN = 5V, rising threshold at ON or INC
Hysteresis
VHYST
Power-Supply Rejection Ratio
PSRR
Propagation Delay
No load, VIN = 5V
ΔVREF, LINE 2.7V ≤ VIN ≤ 13.2V, no load
Line Regulation
tD,COMP
0.575
1.2
1.236
V
1
8
mV
0.6
3
mV
0.6
0.625
V
±1
mV/V
3
2.7V ≤ VIN ≤ 13.2V
10mV overdrive, ON going positive or
negative, INC going negative
INC going positive
mV
μs
10
100
150
200
ms
_______________________________________________________________________________________
3
MAX4271/MAX4272/MAX4273
ELECTRICAL CHARACTERISTICS (continued)
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
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
Input can be driven to the absolute
maximum limit without false output
inversion
Input Voltage Range
Input Bias Current
IB,COMP
ON Pulse Width Low (Note 7)
tRESTART
MIN
TYP
-0.1
0.001
To unlatch a fault MAX4271, MAX4273 with
CTIM = IN
MAX
UNITS
13.2
V
1
μA
μs
20
DIGITAL OUTPUTS (STAT, OUTC)
VSTAT ≤ 13.2, VOUTC ≤ 13.2
Output Leakage Current
Output Voltage Low
VOL
ISINK = 1mA
1
μA
0.4
V
2
s
RETRY TIMING (MAX4272, MAX4273)
Retry Timeout Period
Default Retry
Timeout Period
tRETRY
tRETRY
(default)
100nF capacitor on CTIM (Note 5)
0.5
CTIM = no connection
1
176
µs
UNDERVOLTAGE LOCKOUT (UVLO)
Threshold
VUVLO
Hysteresis
VUVLO,HYST
Delay
tD,UVLO
Startup is initiated when this threshold is
exceeded at IN
2.25
2.67
100
Time the input voltage must exceed
undervoltage lockout before startup is
initiated
100
150
V
mV
200
ms
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.
4
_______________________________________________________________________________________
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
0.4
ON = GND
0.3
0.4
0.2
0.1
0.1
2
4
6
8
10
12
21
-15
10
35
60
180
85
0
2
6
8
10
12
14
TEMPERATURE (°C)
VIN (V)
SLOW COMPARATOR THRESHOLD
vs. INPUT VOLTAGE
FAST COMPARATOR RESPONSE TIME
vs. OVERDRIVE VOLTAGE
FAST COMPARATOR RESPONSE TIME
vs. TEMPERATURE
50.4
50.2
50.0
49.8
TA = +85°C
49.6
400
RESPONSE TIME (ns)
TA = -40°C
49.4
500
450
VIN = 12V
350
VIN = 5V
300
VIN = 12V
400
350
VIN = 5V
300
VIN = 3V
250
250
VIN = 3V
49.2
49.0
2
4
6
8
10
12
200
200
14
1
10
100
1000
-40
-15
10
35
60
VIN (V)
OVERDRIVE VOLTAGE (mV)
TEMPERATURE (°C)
FAST COMPARATOR THRESHOLD
vs. INPUT VOLTAGE
TIME TO FAST DISCHARGE GATE
vs. CGATE
STARTUP PERIOD
vs. INPUT VOLTAGE
TA = -40°C
204
202
TA = +25°C
200
198
TA = +85°C
196
194
10k
1k
VIN = 12V
100
VIN = 5V
10
35
33
31
310
CTIM = 1nF
TIME IN μs
290
29
27
270
VIN = 3V
1
CTIM = 100nF
TIME IN ms
330
tSTART (μs)
206
NO EXTERNAL MOSFET
DISCHARGE TO VGATE = 0.1V
85
MAX4271/3-09
350
MAX4271/3-08
208
100k
TIME TO DISCHARGE GATE (μs)
MAX4271/3-07
210
18
MAX4271/3-06
TA = +25°C
50.6
450
MAX4271/3-04
50.8
VFC,TH (mV)
4
19
VIN (V)
51.0
0
20
CSPD = 0
TIME IN μs
190
0
-40
14
22
210
200
RESPONSE TIME (ns)
0
VIN = 3V
0.3
0.2
0
VSC,TH (mV)
0.5
23
CSPD = 110nF
TIME IN ms
220
0.6
24
tCSPD (ms)
0.5
0.7
230
tCSPD (μs)
0.6
VIN = 12V
VIN = 5V
0.8
MAX4271/3-05
SUPPLY CURRENT (mA)
0.7
0.9
SUPPLY CURRENT (mA)
ON = VIN
IGATE = 10μA
ON = VIN
MAX4271/3-03
240
MAX4271/3-02
0.9
0.8
1.0
MAX4271/3-01
1.0
SLOW COMPARATOR
RESPONSE TIME vs. INPUT VOLTAGE
SUPPLY CURRENT vs. TEMPERATURE
192
190
0
2
4
6
8
VIN (V)
10
12
14
0.1
0.01
0.1
1
10
CGATE (nF)
100
1000
25
250
0
2
4
6
8
10
12
14
VIN (V)
_______________________________________________________________________________________
5
tSTART (ms)
SUPPLY CURRENT vs. INPUT VOLTAGE
MAX4271/MAX4272/MAX4273
Typical Operating Characteristics
(VIN = 5V, RSENSE = 100mΩ, CBOARD = 47µF, TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)
(VIN = 5V, RSENSE = 100mΩ, CBOARD = 47µF, TA = +25°C, unless otherwise noted.)
GATE CHARGE CURRENT
vs. GATE VOLTAGE
VIN = 3V
1.2
VIN = 12V
100
VGATE = 0
IGATE (μA)
1.0
0.8
0.6
VIN = 12V
125
80
VIN = 5V
100
VIN = 5.0V
VIN = 3.0V
60
VIN = 5V
75
40
50
20
25
VIN = 3V
0.4
0.2
0
0
2
4
6
8
10 12 14 16 18 20
2
4
6
8
10 12 14 16 18 20
-40
10
35
60
VGATE (V)
TEMPERATURE (°C)
GATE VOLTAGE vs. INPUT VOLTAGE
SLOW GATE DISCHARGE CURRENT
vs. GATE VOLTAGE
TIME TO CHARGE GATE
vs. CGATE
300
IGATE (μA)
TA = +25°C
15
TA = -40°C
10
VIN = 3V
250
200
VIN = 5V
150
VIN = 12V
100
5
NO EXTERNAL MOSFET
0
0
2
4
6
8
10
12
0
14
2
4
6
8
100
VIN = 12V
TO VGATE = 17V
10
1
VIN = 5V
TO VGATE = 10V
0.1
VIN = 3V
TO VGATE = 6V
0.01
TRIGGERED BY A FAULT
OR BY ON FALLING
50
MAX4271/3-14
TA = +85°C
350
0.001
0.01
10 12 14 16 18 20
0.1
1
10
100
VGATE (V)
CGATE (nF)
FAST GATE DISCHARGE CURRENT
vs. VIN
SLOW GATE DISCHARGE CURRENT
vs. TEMPERATURE
TIME TO SLOW DISCHARGE GATE
vs. CGATE
350
VIN = 3V
300
IGATE (μA)
3.0
2.5
250
200
150
2.0
VIN = 5V, 12V
100
1.5
FALLING VIN
0
1.0
3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0
VIN (V)
VGATE = VIN
TRIGGERED BY A FAULT
OR BY ON FALLING
50
-40
-15
10
1000
TIME TO DISCHARGE GATE (ms)
MAX4271/3-16
3.5
MAX4271/3-15
RISING VIN
400
100
NO EXTERNAL MOSFET
DISCHARGE TO VGATE = 0.1V
VIN = 12V
10
1
VIN = 5V
0.1
0.01
35
TEMPERATURE (°C)
60
85
1000
MAX4271/3-17
VIN (V)
4.0
85
1000
TIME TO CHARGE GATE (ms)
20
400
MAX4271/3-13a
IGATE = 10μA
0
-15
VIN (V)
25
VGATE (V)
0
0
MAX4271/3-13
0
6
150
IGATE (μA)
1.4
120
MAX4271/3-12
VIN = 12V
MAX4271/3-10
FAST GATE DISCHARGE CURRENT (mA)
1.8
1.6
GATE CHARGE CURRENT
vs. TEMPERATURE
MAX4271/3-11
FAST GATE DISCHARGE CURRENT
vs. VGATE
FAST GATE DISCHARGE CURRENT (mA)
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
0.001
0.01
VIN = 3V
0.1
1
10
CGATE (nF)
_______________________________________________________________________________________
100
1000
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
MAX4271/3-20
MAX4271/3-19
MAX4271/3-18
2.4
FAST GATE DISCHARGE CURRENT (mA)
MAX4271/MAX4272
TURN-OFF TIME
(EXTERNAL CGATE = 22nF, CBOARD = 470μF)
MAX4271/MAX4272
TURN-OFF TIME (CBOARD = 470μF)
FAST GATE DISCHARGE CURRENT
vs. TEMPERATURE
VIN = 3V
VGATE = VIN
2.2
ON
ON
VGATE
2V/div
ILOAD
(1A/div)
2.0
ILOAD
1A/div
0
0
1.8
VOUT
2V/div
1.6
VOUT
(2V/div)
1.4
VIN = 5V, 12V
1.2
VGATE
(2V/div)
0
0
1.0
10
35
60
85
200μs/div
CBOARD = 470μF, RSENSE = 100mΩ,
CGATE = 22nF, RS = 0
50μs/div
CBOARD = 470μF, RSENSE = 100mΩ,
CGATE = 0
TEMPERATURE (°C)
MAX4273
TURN-OFF TIME
(CBOARD = 470μF)
MAX4273
TURN-OFF TIME
(EXTERNAL CGATE = 22nF, CBOARD = 470μF)
ON COMPARATOR THRESHOLD
vs. INPUT VOLTAGE
MAX4271/3-20b
MAX4271/3-20a
0.605
ON
ON
VGATE
2V/div
ILOAD
1A/div
MAX4271/3-21
-15
VGATE
2V/div
ILOAD
1A/div
0
0
VOUT
2V/div
VOUT
2V/div
0
0
ON COMPARATOR THRESHOLD (V)
-40
0.603
RISING
0.601
FALLING
0.599
0.597
0.595
50μs/div
20μs/div
0
2
4
6
8
10
12
14
VIN (V)
UVLO THRESHOLD VOLTAGE
vs. TEMPERATURE
}
}
0.6000
VIN = 3V
0.5975
155
RISING
UVLO DELAY (ms)
VIN = 5V
0.6025
2.55
UVLO THRESHOLD (V)
VIN = 12V
0.6050
UVLO DELAY vs. TEMPERATURE
2.50
2.45
FALLING
2.40
-40
-15
10
35
TEMPERATURE (°C)
60
85
VIN = 5V, 12V
VIN = 3V
150
145
2.35
2.30
0.5950
160
MAX4271/3-26
2.60
MAX4271/3-22
0.6075
FALLING RISING
ON COMPARATOR THRESHOLD (V)
0.6100
MAX4271/3-27
ON-COMPARATOR THRESHOLD
vs. TEMPERATURE
140
-40
-15
10
35
TEMPERATURE (°C)
60
85
-40
-15
10
35
60
85
TEMPERATURE (°C)
_______________________________________________________________________________________
7
MAX4271/MAX4272/MAX4273
Typical Operating Characteristics (continued)
(VIN = 5V, RSENSE = 100mΩ, CBOARD = 47µF, TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)
(VIN = 5V, RSENSE = 100mΩ, CBOARD = 47µF, TA = +25°C, unless otherwise noted.)
INC THRESHOLD vs. INPUT VOLTAGE
FALLING
0.595
0.575
1.2038
RISING
612
610
608
FALLING
6
8
10
12
14
1.2034
1.2032
1.2030
1.2028
1.2026
1.2024
602
1.2022
16
1.2020
-40
-15
INPUT VOLTAGE (V)
10
35
60
85
3
5
7
TEMPERATURE (°C)
1.2035
950
CTIM = 100nF
945
RETRY TIMEOUT (ms)
1.2030
1.2025
1.2020
1.2015
940
935
930
1.2010
925
1.2005
920
1.2000
-40
-15
10
35
60
5
7
9
11
13
INPUT VOLTAGE (V)
RETRY TIMEOUT PERIOD
vs. TEMPERATURE
STARTUP TIME (CBOARD = 470μF)
15
MAX4271/3-34
MAX4271/3-33
990
RETRY PERIOD (ms)
3
85
TEMPERATURE (°C)
995
12V
ON
VGATE
2V/div
ILOAD
1A/div
985
980
VOUT
2V/div
5V
975
970
3V
965
-40
-15
10
35
TEMPERATURE (°C)
8
11
RETRY TIMEOUT PERIOD
vs. INPUT VOLTAGE
MAX4271/3-31
1.2040
9
INPUT VOLTAGE (V)
REFERENCE VOLTAGE
vs. TEMPERATURE
REFERENCE VOLTAGE (V)
1.2036
604
600
4
MAX4271/3-30
MAX4271/3-29
614
606
0.585
1.2040
MAX4271/3-32
0.605
616
THRESHOLD (mV)
0.615
618
REFERENCE VOLTAGE (V)
RISING
MAX4273
REFERENCE VOLTAGE
vs. INPUT VOLTAGE
INC THRESHOLD vs. TEMPERATURE
620
MAX4271/3-28
0.625
THRESHOLD (V)
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
60
85
500μs/div
CBOARD = 470μF, RSENSE = 100mΩ,
CTIM = 10nF, CGATE = 0
_______________________________________________________________________________________
13
15
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
(VIN = 5V, RSENSE = 100mΩ, CBOARD = 47µF, TA = +25°C, unless otherwise noted.)
STARTUP TIME (CBOARD = 0)
TURN-OFF TIME (CBOARD = 0)
MAX4271/3-35
MAX4271/3-37
ON
VGATE
2V/div
ON
VGATE
2V/div
ILOAD
1A/div
0
VOUT
2V/div
VOUT
2V/div
0
100μs/div
CBOARD = 0, RSENSE = 100mΩ,
CTIM = 10nF, CGATE = 0
50μs/div
CBOARD = 0, RSENSE = 100mΩ,
CGATE = 0, RS = 0
Pin Description
PIN
MAX4271
MAX4272
MAX4273
FUNCTION
NAME
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.
—
1
RTH
—
2
AUXVCC
1
3
IN
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
—
7
LLMON
4
8
GND
Ground
CEXT
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.
Input Voltage. Connect to +2.7V to +13.2V supply; 15V absolute maximum voltage
rating.
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.
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.
—
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.
_______________________________________________________________________________________
9
MAX4271/MAX4272/MAX4273
Typical Operating Characteristics (continued)
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
Pin Description (continued)
PIN
MAX4271
MAX4272
MAX4273
FUNCTION
NAME
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.
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.
8
13
ON
—
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.
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 parameters 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
• 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 controlling the external MOSFET gate voltage
OR
2) Limiting the current to the load by regulating the voltage across the external current-sense resistor
• Fast comparator threshold
10
______________________________________________________________________________________
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
MAX4271/MAX4272/MAX4273
CSPD
VIN
CSPD
IN
6μA
MAX4271
MAX4272
2.45V
6μA
VSC,TH
50mV
SLOW COMPARATOR
RSENSE
INPUT
UVLO
VSC,TH
200mV
FAST COMPARATOR
150ms
DELAY
ON
VIN RISING
SENSE
GATE
DRIVE
DISCHARGE
STAT
CHARGE
PUMP
(1MHz)
ENABLE
VIN
LOGIC
CONTROL
0.1V
4μA
M1
GATE
N
GATE
OVLO
CTIM
ON
ON COMPARATOR
CTIM
0.6V
VOUT
GND
Figure 1. MAX4271/MAX4272 Functional Diagram
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 external 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 discharged.
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.
______________________________________________________________________________________
11
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
CSPD
VIN
AUXVCC
IN
VIN
2.45V
VFC,TH = 50mV
6μA
MAX4273
6μA
REF
INPUT
UVLO
REF
1.2V
150ms
DELAY
ON
VIN RISING
RSENSE
RTH
VFC,TH = 200mV
SLOW COMPARATOR
RTH
FAST COMPARATOR
VFC,TH =
50mV TO 750mV
10μA
AUXVCC
SENSE
CEXT
CEXT
AUXVCC
DISCHARGE
ENABLE
STAT
CHARGE PUMP
1MHz
0.1V
VIN
LOGIC
CONTROL
Q1
GATE DRIVE
0.1V
4μA
GATE
N
GATE
OVLO
OUTPUT
OVLO
LLMON
CTIM
CTIM
VIN
4μA
ON
ON COMPARATOR
CTON
0.6V
CTON
RESET COMPARATOR
OUTC
150ms
DELAY ON INC RISING
INC
0.6V
VOUT
GND
Figure 2. MAX4273 Functional Diagram
12
______________________________________________________________________________________
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
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 comparator threshold is set at 50mV and has a default delay of
20µs (CSPD floating), allowing it to ignore power-supply 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 threshold for longer than the slow comparator’s set response
time.
The discharge rate depends on the N-FET gate capacitance 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 condition 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.
STAT
ON
STAT
tSTART
VGATE
VGATE
2.7V TO 6V
2.7V TO 6V
VOUT
VOUT
VTH
VGATE
VOUT
CBOARD = LARGE
IFAST, SET
ILIM
CBOARD = 0
ILOAD
ILOAD
tON
Figure 3. Startup Waveforms
tOFF
Figure 4. Response to a Fault Condition
______________________________________________________________________________________
13
MAX4271/MAX4272/MAX4273
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 1kΩ resistor
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.
MAX4271/MAX4272/MAX4273
3V to 12V Current-Limiting Hot-Swap Controllers
with Autoretry, DualSpeed/BiLevel Fault Protection
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 discharges 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 capacitance 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 connected 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 external 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 overcurrent 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 dissipation 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 condition 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
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