General Description
The MAX6397/MAX6398 are small, high-voltage over-
voltage protection circuits. These devices disconnect
the output load or limit the output voltage during an
input overvoltage condition. These devices are ideal for
applications that must survive high-voltage transients
such as those found in industrial applications.
The MAX6397/MAX6398 monitor the input or output
voltages and control an external n-channel MOSFET to
isolate or limit the load from overvoltage transient energy.
When the monitored input voltage is below the user-
adjustable overvoltage threshold, the external n-channel
MOSFET is turned on by the GATE output. In this mode,
the internal charge pump fully enhances the n-channel
MOSFET with a 10V gate-to-source voltage.
When the input voltage exceeds the overvoltage threshold,
the protection can disconnect the load from the input by
quickly forcing the GATE output low. In some applications,
disconnecting the output from the load is not desirable. In
these cases, the protection circuit can be configured to
act as a voltage limiter where the GATE output sawtooths
to limit the voltage to the load.
The MAX6397 also offers an always-on linear regulator
that is capable of delivering up to 100mA of output current.
This high-voltage linear regulator consumes only 37µA of
quiescent current.
The regulator is offered with output options of 5V, 3.3V,
2.5V, or 1.8V. An open-drain, power-good output (POK)
asserts when the regulator output falls below 92.5% or
87.5% of its nominal voltage.
The MAX6397/MAX6398 include internal thermal-
shutdown protection, disabling the external MOSFET
and linear regulator if the chip reaches overtemperature
conditions. The devices operate over a wide 5.5V to
72V supply voltage range, are available in small TDFN
packages, and are fully specified from -40°C to +125°C.
Applications
●Industrial
●FireWire®
●Notebook Computers
●Wall Cube Power Devices
Features
●5.5V to 72V Wide Supply Voltage Range
●Overvoltage Protection Controllers Allow User to Size
External n-Channel MOSFETs
●Internal Charge-Pump Circuit Ensures MOSFET
Gate-to-Source Enhancement for Low RDS(ON)
Performance
●Disconnect or Limit Output from Input During
Overvoltage Conditions
●Adjustable Overvoltage Threshold
●Thermal-Shutdown Protection
●Always-On, Low-Current (37µA) Linear Regulator
Sources Up to 100mA (MAX6397)
●Fully Specified from -40°C to +125°C (TJ)
●Small, Thermally Enhanced 3mm x 3mm TDFN Package
19-3668; Rev 6; 7/14
*Replace “-T” with “+T” for lead(Pb)-free/RoHS-compliant packages.
**EP = Exposed pad.
The MAX6397 linear regulator is offered in four output
voltage options and a choice of a 92.5% or 87.5% POK
threshold assertions. See the Selector Guide.
FireWire is a registered trademark of Apple Computer, Inc. Pin Configurations continued at end of data sheet.
Selector Guide and Typical Operating Circuit appear at end
of data sheet.
PART TEMP RANGE PIN-PACKAGE
MAX6397_ATA-T* -40°C to +125°C 8 TDFN-EP**
MAX6398ATT-T* -40°C to +125°C 6 TDFN-EP**
MAX6397
8
REG
6
GATE
7
OUT
5
GND
3
SHDN
21
IN
TDFN
TOP VIEW
*EP
4
POKSET
*EXPOSED PAD. CONNECT TO GND.
MAX6397/MAX6398 Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
Pin Congurations
Ordering Information
EVALUATION KIT AVAILABLE
(All pins referenced to GND, unless otherwise noted.)
IN, GATE, OUT ...................................................... -0.3V to +80V
SHDN .........................................................-0.3V to (VIN + 0.3V)
GATE to OUT .......................................................... -0.3 to +20V
SET, REG, POK ....................................................-0.3V to +12V
Maximum Current:
IN, REG ........................................................................350mA
All Remaining Pins .............................................................50mA
Continuous Power Dissipation (TA = +70°C)
6-Pin TDFN (derate 18.2mW/°C above +70°C) ........1455mW
8-Pin TDFN (derate 18.2mW/°C above +70°C) ........1455mW
Operating Temperature Range (TA) ................. -40°C to +125°C
Junction Temperature ...................................................... +150°C
Storage Temperature Range ............................ -65°C to +150°C
Lead Temperature ...........................................................+300°C
(VIN = 14V; CGATE = 6000pF, CREG = 4.7µF, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = TJ = +25°C.)
(Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Supply Voltage Range VIN 5.5 72 V
Input Supply Current
SHDN = high, no load (MAX6397) 118 140
µA
SHDN = high, (MAX6398) 104 130
SHDN = low, no load (MAX6397) 37 45
SHDN = low, (MAX6398) 11 20
IN Undervoltage Lockout VIN rising, enables GATE 4.66 5 5.50 V
IN Undervoltage-Lockout
Hysteresis VIN falling, disables GATE 175 mV
SET Threshold Voltage VTH With respect to GND 1.181 1.215 1.248 V
SET Threshold Hysteresis VHYST 4 %
SET Input Current ISET -50 +50 nA
Startup Response Time tSTART SHDN rising (Note 2) 100 µs
GATE Rise Time GATE rising from GND to VOUT + 8V,
CGATE = 6000pF, OUT = GND 1 ms
SET-to-GATE Propagation
Delay tOV SET rising from VTH - 100mV to VTH + 100mV 0.75 µs
GATE Output High Voltage VOH
VOUT = VIN = 6V, RGATE to IN = 1MΩ VIN +
3.8V
VIN +
4.2V
VIN +
4.6V V
VOUT = VIN; VIN ≥ 14V, RGATE to IN = 1MΩ VIN +
8.5V
VIN +
9.2V
VIN +
11.5V
GATE Output Low Voltage VOL GATE sinking 20mA, VOUT = GND 0.38 V
GATE Charge-Pump Current IGATE GATE = GND 75 µA
GATE-to-OUT Clamp Voltage VCLMP 13 18 V
SHDN Logic-High Input Voltage VIH 1.4
SHDN Logic-Low Input Voltage VIL 0.4
SHDN Input Pulldown Current VSHDN = 2V, SHDN is internally pulled
down to GND 1 µA
Thermal Shutdown (Note 3) +150 °C
Thermal-Shutdown Hysteresis 20 °C
REGULATOR (MAX6397)
Ground Current IGND SHDN = GND IREG = 1mA 40 48 µA
IREG = 100mA 60
MAX6397/MAX6398 Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
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Absolute Maximum Ratings
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 = 14V; CGATE = 6000pF, CREG = 4.7µF, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = TJ = +25°C.)
(Note 1)
Note 1: Specifications to TA = -40°C are guaranteed by design and not production tested.
Note 2: The MAX6397/MAX6398 power up with the external FET in off mode (VGATE = GND). The external FET turns on tSTART
after the device is powered up and all input conditions are valid.
Note 3: For accurate overtemperature-shutdown performance, place the device in close thermal contact with the external MOSFET.
Note 4: Dropout voltage is defined as VIN - VREG when VREG is 2% below the value of VREG for VIN = VREG (nominal) + 2V.
Note 5: Operations beyond the thermal dissipation limit may permanently damage the device.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
REG Output Voltage
(VIN ≥ VREG + 1.8V) VREG
MAX6397L/M IREG = 1mA 4.925 5 5.120
V
1mA < IREG < 100mA 4.85 5.15
MAX6397S/T IREG = 1mA 3.243 3.3 3.36
1mA < IREG < 100mA 3.201 3. 36
MAX6397Y/Z IREG = 1mA 2.246 2.5 2.542
1mA < IREG < 100mA 2.41 2.55
MAX6397V/W IREG = 1mA 1.76 1.8 1.837
mV/V
1mA < IREG < 100mA 1.715 1.837
Dropout Voltage (Note 4) ∆VDO
5.5V ≤ VIN ≤ 72V, IREG = 1mA, VREG = 5V 0.12
5.5V ≤ VIN ≤ 72V, IREG = 100mA, VREG = 5V 1.2
Current Limit VIN = 14V 150 300 mA
Overvoltage-Protection
Threshold VOVP 105 % of
VREG
Overvoltage-Protection Sink
Current IOVP VREG = 1.1 x VREG (Nominal) 15 mA
Line Regulation (Note 5) ∆VREG/
∆VREG
6.5V ≤ VIN ≤ 72V, IREG = 10mA, VREG = 5V 0.22
mV/mA5.5V ≤ VIN ≤ 72V, IREG = 1mA, VREG = 5V 0.05
5.5V ≤ VIN ≤ 72V, IREG = 100mA, VREG = 5V 1.5
Load Regulation ∆VREG /
∆IREG 1mA ≤ IREG ≤ 100mA, VREG = 5V 0.8 mV/mA
Power-Supply Rejection Ratio IREG = 10mA, f = 100Hz, 0.5VP-P 55 dB
Startup Response Time tSTART RREG = 500Ω, VREG = 5V, CREG = 4.7µF 180 µs
POK Assertion Threshold
(MAX6397 Only) VPOK_TH
L 4.500 4.67 4.780
V
M 4.230 4.375 4.500
T 2.966 3.053 3.140
S 2.805 2.892 2.970
Z 2.250 2.304 2.375
Y 2.125 2.188 2.250
W 1.590 1.653 1.696
V 1.524 1.575 1.625
REG-to-POK Delay VREG rising or falling 35 µs
POK Leakage Current VPOK = 5V 100 nA
POK Output Low Voltage VOL VIN ≥ 1.5V, ISINK = 1.6mA, POK asserted 0.3 V
MAX6397/MAX6398 Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
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Electrical Characteristics (continued)
(VIN = 14V, CREG = 4.7μF, IREG = 0, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
MAX6397 toc02
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
1007525 500-25
90
100
110
120
130
140
150
160
170
180
80
-50 125
VIN = 14V
VIN = 72V
MAX6397
40
50
60
70
80
90
100
110
120
0 20 40 60 80
SUPPLY CURRENT
vs. INPUT VOLTAGE
MAX6397 toc03
INPUT VOLTAGE (V)
SUPPLY CURRENT (µA)
MAX6398
GATE ON
80
100
90
120
110
130
140
-50 25 50-25 0 75 100 125
SUPPLY CURRENT
vs. TEMPERATURE
MAX6397-98 toc04
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
VIN = 72V
VIN = 14V
MAX6398
GATE ON
20
30
25
40
35
45
50
0 4020 60 80
SHUTDOWN SUPPLY CURRENT
vs. INPUT VOLTAGE (MAX6397)
MAX6397 toc05
INPUT VOLTAGE (V)
SUPPLY CURRENT (µA)
10 30 50 70
REGULATOR ON
GATE OFF
0
6
4
2
8
10
12
14
16
18
20
0 20 40 60 80
SHUTDOWN SUPPLY CURRENT
vs. INPUT VOLTAGE
MAX6397 toc06
INPUT VOLTAGE (V)
SUPPLY CURRENT (µA)
MAX6398
GATE OFF
0
6
4
2
8
10
12
4 12106 8 14 16 18 20 22 24
GATE-DRIVE VOLTAGE
vs. INPUT VOLTAGE
MAX6397 toc07
INPUT VOLTAGE (V)
VGATE - VOUT (V)
VOUT = VIN
40
60
80
100
120
140
160
0 2010 30 40 50 60 70 80
SUPPLY CURRENT
vs. INPUT VOLTAGE
MAX6397 toc01
INPUT VOLTAGE (V)
SUPPLY CURRENT (µA)
MAX6397
GATE ON
4.0
4.6
4.4
4.2
5.0
4.8
5.8
5.6
5.4
5.2
6.0
-50 -25 0 25 50 75 100 125
UVLO THRESHOLD
vs. TEMPERATURE
MAX6397 toc08
TEMPERATURE (°C)
VUVLO (V)
SET THRESHOLD vs. TEMPERATURE
MAX6397 toc09
TEMPERATURE (°C)
SET THRESHOLD (V)
1007525 500-25
1.204
1.208
1.212
1.216
1.220
1.224
1.228
1.232
1.236
1.240
1.200
-50 125
MAX6397/MAX6398 Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
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Typical Operating Characteristics
(VIN = 14V, CREG = 4.7μF, IREG = 0, unless otherwise noted.)
16.0
16.3
16.2
16.1
16.5
16.4
16.9
16.8
16.7
16.6
17.0
-50 -25 0 25 50 75 100 125
GATE-TO-OUT CLAMP VOLTAGE
vs. TEMPERATURE
MAX6397 toc10
TEMPERATURE (°C)
GATE-TO-OUT CLAMP VOLTAGE (V)
0
0.4
0.2
0.8
0.6
1.2
1.0
1.4
1.8
1.6
2.0
0 40 60 8020 100 120 140 160 180
DROPOUT VOLTAGE
vs. REG LOAD CURRENT
MAX6397-98 toc11
REG LOAD CURRENT (mA)
DROPOUT VOLTAGE (V)
MAX6397L
TA = +125°C
TA = +25°C
TA = -40°C
4.90
5.00
4.95
5.10
5.05
5.15
5.20
-40 -10 5 20-25 35 50 65 80 95 110 125
REG OUTPUT VOLTAGE
vs. LOAD CURRENT AND TEMPERATURE
MAX6397 toc12
TEMPERATURE (°C)
REG OUTPUT VOLTAGE (V)
ILOAD = 100mA
ILOAD = 10mA
ILOAD = 50mA
MAX6397L
4.0
4.6
4.4
4.2
4.8
5.0
5.2
0 16012040 80 200 240 280 320 360 400
MAXIMUM REG OUTPUT VOLTAGE
vs. LOAD CURRENT AND TEMPERATURE
MAX6397 toc13
LOAD CURRENT (mA)
REG OUTPUT VOLTAGE (V)
THERMAL
SHUTDOWN
TA = +25°C
TA = +125°C
TA = -40°C
GATE-DRIVE VOLTAGE
vs. TEMPERATURE
MAX6397 toc14
TEMPERATURE (°C)
GATE-DRIVE VOLTAGE (V)
1007525 500-25
10.455
10.460
10.465
10.470
10.475
10.480
10.485
10.490
10.495
10.500
10.450
-50 125
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX6397 toc15
FREQUENCY (Hz)
PSRR (dB)
1M100k10k1k100
-60
-50
-40
-30
-20
-10
0
-70
10 10M
CREG = 10µF
IREG = 10mA
4ms/div
STARTUP WAVEFORM
(RLOAD = 100Ω, CIN = 10µF, COUT = 10µF)
VIN
10V/div
MAX6397 toc16
VGATE
10V/div
VOUT
10V/div
IOUT
200mA/div
400µs/div
STARTUP WAVEFORM FROM SHUTDOWN
(CIN = 10µF, COUT = 10µF)
VSHDN
2V/div
MAX6397 toc17
VGATE
10V/div
VOUT
10V/div
IOUT
200mA/div
RLOAD = 100Ω
MAX6397/MAX6398 Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
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Typical Operating Characteristics (continued)
(VIN = 14V, CREG = 4.7μF, IREG = 0, unless otherwise noted.)
1ms/div
VOLTAGE LIMIT FAULT
VIN
20V/div
MAX6397 toc19
VGATE
20V/div
VOUT
20V/div
VREG
5V/div
VOV = 30V
400µs/div
TRANSIENT RESPONSE
MAX6397 toc20
VIN
10V/div
VREG
100mV/div
CREG = 10µF
IREG = 10mA
1ms/div
REG LOAD-TRANSIENT RESPONSE
VREG
AC-COUPLED
500mV/div
MAX6397 toc21
IREG
100mA/div
CREG = 10µF
1ms/div
REGULATOR STARTUP WAVEFORM
VIN
10V/div
MAX6397 toc22
VPOK
2V/div
VREG
2V/div
IREG = 10mA
200µs/div
OVERVOLTAGE SWITCH FAULT
VIN
20V/div
MAX6397 toc18
VGATE
20V/div
VOUT
20V/div
VREG
5V/div
VOV = 30V
100µs/div
REGULATOR POK ASSERTION
VREG
2V/div
MAX6397 toc23
IREG
200mA/div
VPOK
2V/div
IREG = 0
0V
0V
0A
MAX6397/MAX6398 Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
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Typical Operating Characteristics (continued)
Detailed Description
The MAX6397/MAX6398 are ultra-small, low-current,
high-voltage protection circuits for applications that must
survive high-voltage transient conditions. These devices
monitor the input/output voltages and control an external
n-channel MOSFET to isolate the load or to regulate the
output voltage from overvoltage-transient energy. The
controller allows system designers to size the external
MOSFET to their load current and board size.
The MAX6397/MAX6398 drive the MOSFET’s gate high
when the monitored input voltage is below the adjustable
overvoltage threshold. An internal charge-pump circuit
provides a 5V to 10V gate-to-source drive (see the Typical
Operating Characteristics) to ensure low input-to-load
voltage drops in normal operating modes. When the input
voltage rises above the user-adjusted overvoltage thresh-
old, GATE pulls to OUT, turning off the MOSFET.
The MAX6397/MAX6398 are configurable to operate
as overvoltage-protection switches or as closed-looped
voltage limiters. In overvoltage-protection switch
mode, the input voltage is monitored. When an
overvoltage condition occurs at IN, GATE pulls low,
disconnecting the load from the power source, and then
slowly enhances upon removal of the overvoltage
condition. In overvoltage-limit mode, the output volt-
age is monitored and the MAX6397/MAX6398 regulate
the source of the external MOSFET at the adjusted
overvoltage threshold, allowing devices within the system
to continue operating during an overvoltage condition.
The MAX6397/MAX6398 undervoltage lockout (UVLO)
function disables the devices as long as the input remains
below the 5V (typ) UVLO turn-on threshold. The MAX6397/
MAX6398 have an active-lows SHDN input to turn off the
external MOSFET, disconnecting the load and reducing
power consumption. After power is applied and SHDN is
driven above its logic-high voltage, there is a 100µs delay
before GATE enhancement commences.
The MAX6397 integrates a high input voltage, low-
quiescent-current linear regulator, in addition to an
overvoltage-protector circuit. The linear regulator remains
enabled at all times to power low-current “always-on”
applications (independent of the state of the external
MOSFET). The regulator is offered with several standard
output voltage options (5V, 3.3V, 2.5V, or 1.8V). An open-
drain power-good output notifies the system if the regulator
PIN NAME FUNCTION
MAX6397 MAX6398
1 1 IN Supply Voltage Input. Bypass with a minimum 10µF capacitor to GND.
2 2 SHDN
Shutdown Input. Drive SHDN low to force GATE low, turning off the external n-channel
MOSFET. REG remains active when in shutdown mode. SHDN is internally pulled down
to GND with a 1µA source. Connect to IN for normal operation.
3 3 SET
Overvoltage-Threshold-Adjustment Input. Connect SET to an external resistor voltage-
divider network to OUT (overvoltage limiter) or IN (overvoltage switch) to adjust the
desired overvoltage-limit threshold. Use SET to monitor a system input or output voltage.
4 — POK Open-Drain Output. POK remains low until REG exceeds 92.5% or 87.5% of REG
nominal output voltage. Connect to an external pullup resistor.
5 4 GND Ground
6 5 GATE
Gate-Drive Output. Connect GATE to the gate of an external n-channel MOSFET.
GATE is a charge pump with a 75µA pullup current to 10V (typ) above IN during normal
operation. GATE is quickly shorted to OUT during an overvoltage condition. GATE pulls
low when SHDN is low.
7 6 OUT Output-Voltage-Sense Input. Connect to the source of the external n-channel MOSFET.
8 — REG Regulator Output. Fixed 5.0V, 3.3V, 2.5V, or 1.8V output. REG sources up to 100mA.
Bypass with a minimum 4.7µF capacitor to GND.
— — EP Exposed Pad. Connect to ground plane.
MAX6397/MAX6398 Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
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Pin Description
output falls to 92.5% or 87.5% of its nominal voltage. The
MAX6397’s REG output operates independently of the
SHDN logic input.
The MAX6397/MAX6398 include internal thermal-
shutdown protection, disabling the external MOSFET and
linear regulator if the chip reaches overtemperature condi-
tions.
Linear Regulator (MAX6397 Only)
The MAX6397 is available with 5.0V, 3.3V, 2.5V, and 1.8V
factory-set output voltages. Each regulator sources up to
100mA and includes a current limit of 230mA. The linear
regulator operates in an always-on condition regardless
of the SHDN logic. For fully specified operation, VIN must
be greater than 6.5V for the MAX6397L/M (5V regulator
output). The actual output current may be limited by the
operating condition and package power dissipation.
Power-OK Output
POK is an open-drain output that goes low when REG
falls to 92.5% or 87.5% (see the Selector Guide) of its
nominal output voltage. To obtain a logic-level output,
connect a pullup resistor from POK to REG or another
system voltage. Use a resistor in the 100kΩ range to
minimize current consumption. POK provides a valid
logic-output level down to VIN = 1.5V.
GATE Voltage
The MAX6397/MAX6398 use a high-efficiency charge
pump to generate the GATE voltage. Upon VIN exceed-
ing the 5V (typ) UVLO threshold, GATE enhances 10V
above IN (for VIN ≥14V) with a 75µA pullup current. An
overvoltage condition occurs when the voltage at SET
pulls above its 1.215V threshold. When the threshold is
crossed, GATE falls to OUT within 100ns with a 100mA
(typ) pulldown current. The MAX6397/MAX6398 include
an internal clamp to OUT that ensures GATE is limited to
18V (max) above OUT to prevent gate-to-source damage
to the external FET.
The GATE cycle during overvoltage-limit and overvoltage-
switch modes are quite similar but have distinct charac-
teristics. In overvoltage-switch mode (Figure 2a), GATE
is enhanced to VIN + 10V while the monitored IN volt-
age remains below the overvoltage-fault threshold (SET
< 1.215V). When an overvoltage fault occurs (SET ≥
1.215V), GATE is pulled one diode below OUT, turning
off the external FET and disconnecting the load from the
input. GATE remains low (FET off) as long as VIN is above
the overvoltage-fault threshold. As VIN falls back below
the overvoltage-fault threshold (-5% hysteresis), GATE is
again enhanced to VIN + 10V.
Figure 1. Functional Diagram
Figure 2a. MAX6397/MAX6398 GATE Waveform During
Overvoltage Switch Mode
MAX6397
MAX6398
10V
CHARGE
PUMP
LINEAR
REGULATOR
VPOK_TH
MAX6397 ONLY
THERMAL
PROTECTION
5V
1.23V
UVLO
GATE
OUT
SHDN
REG
POK
GND
IN
SET
VGATE
10V/div
VOUT
10V/div
VIN
10V/div
10ms/div
MAX6397/MAX6398 Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
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In overvoltage-limit mode (Figure 2b), GATE is enhanced
to VIN + 10V. While the monitored OUT voltage remains
below the overvoltage fault threshold (SET < 1.215V).
When an overvoltage fault occurs (SET ≥ 1.215V), GATE
is pulled low one diode drop below OUT until OUT drops
5% below the overvoltage-fault threshold. GATE is then
turned back on until OUT again reaches the overvoltage-
fault threshold and GATE is again turned off.
GATE cycles on-off-on-off-on in a sawtooth waveform until
OUT remains below the overvoltage-fault threshold and
GATE remains constantly on (VIN + 10V). The overvoltage
limiter’s sawtooth GATE output operates the MOSFET in
a switched-linear mode while the input voltage remains
above the overvoltage-fault threshold. The sawtooth
frequency depends on the load capacitance, load current,
and MOSFET turn-on time (GATE charge current and
GATE capacitance).
GATE goes high when the following startup conditions are
met: VIN is above the UVLO threshold, SHDN is high, an
overvoltage fault is not present and the device is not in
thermal shutdown.
Overvoltage Monitoring
When operating in overvoltage mode, the MAX6397/
MAX6398 feedback path (Figure 3) consists of IN, SET’s
internal comparator, the internal gate charge pump, and
the external n-channel MOSFET resulting in a switch-on/
off function. When the programmed overvoltage threshold
is tripped, the internal fast comparator turns off the external
MOSFET, pulling GATE to OUT within tOV and disconnect-
ing the power source from the load. When IN decreases
below the adjusted overvoltage threshold, the MAX6397/
MAX6398 slowly enhance GATE above OUT, reconnecting
the load to the power source.
Overvoltage Limiter
When operating in overvoltage-limiter mode, the
MAX6397/MAX6398 feedback path (Figure 4) consists of
OUT, SET’s internal comparator, the internal gate charge
pump and the external n-channel MOSFET, which results
in the external MOSFET operating as a voltage regulator.
During normal operation, GATE is enhanced 10V above
OUT. The external MOSFET source voltage is monitored
through a resistor-divider between OUT and SET. When
OUT rises above the adjusted overvoltage threshold,
an internal comparator sinks the charge-pump current,
discharging the external GATE, regulating OUT at the
set overvoltage threshold. OUT remains active during
Figure 2b. MAX6397/MAX6398 GATE Waveform During
Overvoltage Limit Mode
Figure 3. Overvoltage Switch Protection Configuration
Figure 4. Overvoltage Limiter Protection Switch Configuration
VGATE
10V/div
VOUT
10V/div
VIN
10V/div
4ms/div
MAX6397
MAX6398
IN
SET
GATE
OUT
GND
VBATT
R1
R2
MAX6397
MAX6398
IN
SET
GATE
OUT
GND
VBATT
R1
R2
COUT
MAX6397/MAX6398 Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
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the overvoltage transients and the MOSFET continues
to conduct during the overvoltage event, operating in
switched-linear mode.
As the transient begins decreasing, OUT fall time will
depend on the MOSFET’s GATE charge, the internal
charge-pump current, the output load, and the tank
capacitor at OUT.
For fast-rising transients and very large-sized MOSFETs,
add an additional external bypass capacitor from GATE to
GND to reduce the effect of the fast-rising voltages at IN.
The external capacitor acts as a voltage-divider working
against the MOSFETs’ drain-to-gate capacitance. For a
6000pF Cgd, a 0.1µF capacitor at GATE will reduce the
impact of the fast-rising VIN input.
Caution must be exercised when operating the MAX6397/
MAX6398 in voltage-limiting mode for long durations.
If the VIN is a DC voltage greater than the MOSFET’s
maximum gate voltage, the FET will dissipate power
continuously. To prevent damage to the external MOSFET,
proper heatsinking should be implemented.
Applications Information
Setting Overvoltage Thresholds
SET provides an accurate means to set the overvoltage
level for the MAX6397/MAX6398. Use a resistor-divider
to set the desired overvoltage condition (Figure 5). SET
has a rising 1.215V threshold with a 5% falling hysteresis.
Begin by selecting the total end-to-end resistance,
RTOTAL = R1 + R2. Choose RTOTAL to yield a total
current equivalent to a minimum 100 x ISET (SET’s input
bias current) at the desired overvoltage threshold.
For example:
With an overvoltage threshold set to 20V:
RTOTAL < 20V/(100 x ISET)
where ISET is SET’s 50nA input bias current.
RTOTAL < 4MΩ
Use the following formula to calcue R2:
TOTAL
TH OV
R
R2 V V
= ×
where VTH is the 1.215V SET rising threshold and VOV is
the overvoltage threshold.
R2 = 243kΩ, use a 240kΩ standard resistor.
RTOTAL = R2 + R1, where R1 = 3.76MΩ.
Use a 3.79MΩ standard resistor.
A lower value for total resistance dissipates more power
but provides slightly better accuracy.
Figure 5. Setting the MAX6397/MAX6398 Overvoltage Threshold
MAX6397
MAX6398
IN
SET
GATE
OUT
GND
IN
R1
R2
MAX6397
MAX6398
IN
SET
GATE
OUT
GND
R1
R2
IN
MAX6397/MAX6398 Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
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Reverse-Battery Protection
Use a diode or p-channel MOSFET to protect the
MAX6397/MAX6398 during a reverse-battery insertion
(Figures 6a, 6b). Low p-channel MOSFET on-resistance
of 30mΩ or less yields a forward-voltage drop of only a
few millivolts (versus hundreds of millivolts for a diode,
Figure 6a) thus improving efficiency.
Connecting a positive battery voltage to the drain of Q1
(Figure 6b) produces forward bias in its body diode, which
clamps the source voltage one diode drop below the drain
voltage. When the source voltage exceeds Q1’s threshold
voltage, Q1 turns on. Once the FET is on, the battery is
fully connected to the system and can deliver power to the
device and the load.
An incorrectly inserted battery reverse-biases the FET’s
body diode. The gate remains at the ground potential.
The FET remains off and disconnects the reversed
battery from the system. The zener diode and resistor
combination prevent damage to the p-channel MOSFET
during an overvoltage condition.
Figure 6. Reverse-Battery Protection Using a Diode or p-Channel MOSFET
MAX6397
MAX6398
LOAD
(b)
VBATT
Q1
GND
IN
OUT
GATE
MAX6397
MAX6398
LOAD
(a)
VBATT
GND
IN
OUT
GATE
MAX6397/MAX6398 Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
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REG Capacitor Selection for Stability
For stable operation over the full temperature range
and with load currents up to 100mA, use ceramic
capacitor values greater than 4.7µF. Large output
capacitors help reduce noise, improve load-transient
response, and power-supply rejection at REG. Note that
some ceramic dielectrics exhibit large capacitance and
ESR variation with temperature. At lower temperatures, it
may be necessary to increase capacitance.
Under normal conditions, use a 10µF capacitor at IN.
Larger input capacitor values and lower ESR provide
better supply-noise rejection and line-transient response.
Inrush/Slew-Rate Control
Inrush current control can be implemented by placing a
capacitor at GATE (Figure 7) to slowly ramp up the GATE,
thus limiting the inrush current and controlling GATE’s
slew rate during initial turn-on. The inrush current can be
approximated using the followng formula:
OUT
INRUSH GATE LOAD
GATE
C
I I I
C
= ×+
where IGATE is GATE’s 75µA sourcing current, ILOAD
is the load current at startup, and COUT is the output
capacitor.
Input Transients Clamping
When the external MOSFET is turned off during an
overvoltage occurrence, stray inductance in the power
path may cause voltage ringing exceeding the MAX6397/
MAX6398 absolute maximum input (IN) supply rating.
The following techniques are recommended to reduce the
effect of transients:
• Minimize stray inductance in the power path using
wide traces, and minimize loop area including the
power traces and the return ground path.
• Add a zener diode or transient voltage suppressor
(TVS) rated below the IN absolute maximum rating
(Figure 8).
Add a resistor in series with IN to limit transient current
going into the input for the MAX6398 only.
MOSFET Selection
Select external MOSFETs according to the application
current level. The MOSFET’s on-resistance (RDS(ON))
should be chosen low enough to have minimum voltage
drop at full load to limit the MOSFET power dissipation.
Determine the device power rating to accommodate
an overvoltage fault when operating the MAX6397/
MAX6398 in overvoltage-limit mode.
Figure 7. MAX6397/MAX6398 Controlling GATE Inrush Current Figure 8. Protecting the MAX6397/MAX6398 Input from High-
Voltage Transients
MAX6397
MAX6398
LOAD
VBATT
GND
IN
OUT
GATE
CGATE COUT
MAX6397
MAX6398
LOAD
GND
IN
OUT
GATE
VBATT
60V
TVS
1kΩ
MAX6397/MAX6398 Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
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During normal operation, the external MOSFETs dissipate
little power. The power dissipated in normal operation is:
PQ1 = ILOAD2 x RDS(ON).
The most power dissipation will occur during a
prolonged overvoltage event when operating the
MAX6397/MAX6398 in voltage limiter mode, resulting in
high power dissipated in Q1 (Figure 9) where the power
dissipated across Q1 is:
PQ1 = VQ1 x ILOAD
where VQ1 is the voltage across the MOSFET’s drain and
source.
Thermal Shutdown
The thermal-shutdown feature of the MAX6397/
MAX6398 shuts off the linear regulator output (REG),
and GATE if it exceeds the maximum allowable thermal
dissipation. Thermal shutdown also monitors the PCB
temperature of the external nFET when the devices sit on
the same thermal island. Good thermal contact between
the MAX6397/MAX6398 and the external nFET is essential
for the thermal-shutdown feature to operate effectively.
Place the nFET as close as possible to OUT.
When the junction temperature exceeds TJ = +150°C,
the thermal sensor signals the shutdown logic, turning
off REG’s internal pass transistor and the GATE output,
allowing the device to cool. The thermal sensor turns the
pass transistor and GATE on again after the IC’s junction
temperature cools by 20°C. Thermal-overload protection
is designed to protect the MAX6397/MAX6398 and the
external MOSFET in the event of current-limit fault
conditions. For continuous operation, do not exceed
the absolute maximum junction-temperature rating of
TJ = +150°C.
Thermal Shutdown
Overvoltage Limiter Mode
When operating the devices in overvoltage-limit mode
for a prolonged period of time, a thermal shutdown is
possible due to device self-heating. The thermal
shutdown is dependent on a number of different factors:
• The device’s ambient temperature (TA)
• The output capacitor (COUT)
• The output load current (IOUT)
• The overvoltage-threshold limit (VOV)
• The overvoltage-waveform period (tOVP)
• The power dissipated across the package (PDISS)
When OUT exceeds the adjusted overvoltage threshold,
an internal GATE pulldown current is enabled until OUT
drops by 5%. The capacitance at OUT is discharged by
the internal current sink and the external OUT load cur-
rent. The discharge time (∆t1) is approximately:
OV
OUT
OUT GATEPD
V 0.05
t 1 C I I
×
∆=
+
where VOV is the adjusted overvoltage threshold, IOUT
is the external load current and IGATEPD is the GATE’s
internal 100mA (typ) pulldown current.
Figure 9. Power Dissipated Across MOSFETs During an
Overvoltage Fault (Overvoltage Limiter Mode)
Figure 10. MAX6397/MAX6398 Timing Diagram
MAX6397
MAX6398
LOAD
GND
IN
OUT
GATE
VBATT
60V
TVS
SET
VQ1
+ -
ILOAD
VBATT
VMAX
VOV
t2
t1t3
tOVP
GATE
OUT
MAX6397/MAX6398 Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
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When OUT falls 5% below the overvoltage-threshold point,
the internal current sink is disabled and the MAX6397/
MAX6398’s internal charge pump begins recharging
the external GATE voltage. The OUT voltage continues
to drop due to the external OUT load current until the
MOSFET gate is recharged. The time needed to recharge
GATE and re-enhance the external nFET is approximately:
GS(TH) F
ISS
GATE
V V
t2 C I
+
∆=
where CISS is the MOSFET’s input capacitance, VGS(TH)
is the MOSFET’s gate-to-source threshold voltage, VF
is the internal clamp diode forward voltage (VF = 1.5V
typ), and IGATE is the MAX6397/MAX6398 charge-pump
current (75µA typ).
During ∆t2, COUT loses charge through the output load.
The voltage across COUT (∆V2) decreases until the
MOSFET reaches its VGS(TH) threshold and can be
approximated using the following formula:
OUT
OUT
t2
V2 I C
∆
∆=
Once the MOSFET VGS(TH) is obtained, the slope of the
output voltage rise is determined by the MOSFET QG
charge through the internal charge pump, with respect to
the drain potential. The time for the OUT voltage to rise
again to the overvoltage threshold can be approximated
using the following formula:
GD OUT
GS_QGD GATE
QV
t3
VI
∆
∆≅ ×
where ∆VOUT = ( VOV x 0.05) + ∆V2.
The total period of the overvoltage waveform can be
summed up as follows:
tOVP = ∆t1 + ∆t2 + ∆t3
The MAX6397/MAX6398 dissipate the most power during
an overvoltage event when IOUT = 0 (COUT is discharged
only by the internal current sink). The maximum power
dissipation can be approximated using the following
equation:
DISS OV GATEPD
OVP
t1
P V 0.975 I t
∆
=×× ×
∆
The die temperature (TJ) increase is related to θJC
(8.3°C/W and 8.5°C/W for the MAX6397 and MAX6398,
respectively) of the package when mounted correctly
with a strong thermal contact to the circuit board. The
MAX6397/MAX6398 thermal shutdown is governed by
the following equation:
TJ = TA + PDISS x (θJC + θCA) < 170°C
(typical thermal-shutdown temperature)
For the MAX6397, the power dissipation of the internal
linear regulator must be added to the overvoltage-
protection circuit power dissipation to calculate the die
temperature. The linear regulator power dissipation is
calculated using the following equation:
PREG = (VIN − VREG) (IREG)
For example, using an IRFR3410 100V n-channel
MOSFET, Figure 11 illustrates the junction temperature
vs. output capacitor with IOUT = 0, TA = +125°C, VOV
< 16V,VF = 1.5V, IGATE = 75mA, and IGATEPD =
100mA. Figure 11 shows the relationship between output
capacitance versus die temperature for the conditions
listed above.
Figure 11. Junction Temperature vs. COUT
OUTPUT CAPACITANCE (µF)
JUNCTION TEMPERATURE (°C)
10010
120
130
140
150
160
170
180
1 1000
IOUT = 0
TA = +125°C
THERMAL SHUTDOWN
CGATE = 0
CGATE = InF
CGATE = 10nF
CGATE = ADDITIONAL
CAPACITANCE FROM GATE TO GND
MAX6397/MAX6398 Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
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An additional capacitor can be added to GATE and GND
to shift the curves as this increases ∆t1. These values
are used for illustration only. Customers must verify
worst-case conditons for their specific application.
OUTPUT Current Calculation
The MAX6397 high input voltage (+72V max) provides
up to 100mA of output current at REG. Package power
dissipation limits the amount of output current available
for a given input/output voltage and ambient
temperature. Figure 12 depicts the maximum power
dissipation curve for the MAX6397. The graph assumes
that the exposed metal pad of the MAX6397 package is
soldered to 1in2 of PCB copper. Use Figure 10 to determine the
allowable package dissipation for a given ambient
temperature. Alternately, use the following formula to
calculate the allowable package dissipation:
PDISS = 1.455W for TA ≤ +70°C
Maximum power dissipation = 1.455 - 0.0182 (TA - 70°C)
for +70°C ≤ TA ≤ +125°C
where 0.0182 W/°C is the MAX6397 package-thermal
derating.
After determining the allowable package dissipation,
calculate the maximum output current using the following
formula:
DISS
OUT(MAX)
IN REG
P
I 100mA
VV
= ≤
−
Figure 12. Maximum Power Dissipation vs. Temperature
TEMPERATURE (°C)
PD (W)
14012080 10040 6020
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
0
0 160
DERATE 18.2mW/°C
ABOVE +70°C
1.455W
MAX6397
GATE
POK
REG
IN
SHDN GND
SET
OUT
ALWAYS-ON
µC
VCC
RESET
GPIO
12V IN
DC-DC
CONVERTER
OUTIN
GND
µC
MAX6397/MAX6398 Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
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Typical Application Circuit
PART REG OUTPUT
VOLTAGE (V)
POK ASSERTION
THRESHOLD (%)
TOP
MARK
MAX6397LATA 5.0 92.5 ANN
MAX6397MATA 5.0 87.5 ANO
MAX6397SATA 3.3 87.5 ANQ
MAX6397TATA 3.3 92.5 ANP
MAX6397YATA 2.5 87.5 ANK
MAX6397ZATA 2.5 92.5 ANJ
MAX6397VATA 1.8 87.5 ANM
MAX6397WATA 1.8 92.5 ANL
MAX6398ATT — — AJD
MAX6397
MAX6398
IN
SETREG REG
GATE
OUT
GND
VBATT
R1
R2
MAX6397
MAX6398
IN
SET
GATE
OUT
GND
R1
R2
VBATT
COUT COUT
DC-DC
CONVERTER
DC-DC
CONVERTER
OVERVOLTAGE LIMITER CONTROLLER OVERVOLTAGE SWITCH CONTROLLER
6
GATE
5
OUT
4
SET
1 2
GND
3
SHDN
MAX6398
IN
TDFN
TOP VIEW
*EP
*EXPOSED PAD. CONNECT TO GND.
MAX6397/MAX6398 Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
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Typical Operating Circuit
Pin Congurations (continued) Selector Guide
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND PATTERN
NO.
6 TDFN T633+2 21-0137 90-0059
8 TDFN T833+2 21-0137 90-0058
MAX6397/MAX6398 Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
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Package Information
For the latest package outline information and land patterns
(footprints), go to www.maximintegrated.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
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 5/05 Initial release —
3 1/07 Changed formula and updated Figure 13 caption title 1, 14, 15, 17
4 3/07 Updated Electrical Characteristics table. 1, 3, 18
5 1/09 Updated Electrical Characteristics table. 3
6 7/14
Deleted automotive references in General Description, Applications, and Detailed
Description sections; deleted Load Dump section and Figure 5 (renumbering the
remaining gures) 1, 7, 10–15
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
MAX6397/MAX6398 Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
© 2014 Maxim Integrated Products, Inc.
│
18
Revision History
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
