General Description
The MAX6397/MAX6398 are small, high-voltage overvolt-
age protection circuits. These devices disconnect the
output load or limit the output voltage during an input
overvoltage condition. These devices are ideal for appli-
cations that must survive high-voltage transients such as
those found in automotive and 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 thresh-
old, 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-shut-
down 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
Automotive
Industrial
FireWire®
Notebook Computers
Wall Cube Power Devices
Features
o5.5V to 72V Wide Supply Voltage Range
oOvervoltage Protection Controllers Allow User to
Size External n-Channel MOSFETs
oInternal Charge-Pump Circuit Ensures MOSFET
Gate-to-Source Enhancement for Low RDS(ON)
Performance
oDisconnect or Limit Output from Input During
Overvoltage Conditions
oAdjustable Overvoltage Threshold
oThermal-Shutdown Protection
oAlways-On, Low-Current (37µA) Linear Regulator
Sources Up to 100mA (MAX6397)
oFully Specified from -40°C to +125°C (TJ)
oSmall, Thermally Enhanced 3mm x 3mm TDFN
Package
MAX6397/MAX6398
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
________________________________________________________________
Maxim Integrated Products
1
MAX6397
8
REG
6
GATE
7
OUT
5
GND
3
SHDN
21
IN
TDFN
TOP VIEW
*EP
4
POKSET
*EXPOSED PAD. CONNECT TO GND.
Pin Configurations
Ordering Information
19-3668; Rev 5; 1/09
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.
*
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.
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**
Selector Guide and Typical Operating Circuit appear at end
of data sheet.
Pin Configurations continued at end of data sheet.
FireWire is a registered trademark of Apple Computer, Inc.
EVALUATION KIT
AVAILABLE
MAX6397/MAX6398
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
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)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional oper-
ation 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.
(All pins referenced to GND, unless otherwise noted.)
IN, GATE, OUT ............................................................-0.3V to +80V
SHDN ..................................................................-0.3V to (IN + 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
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Supply Voltage Range VIN 5.5 72 V
SHDN = high, no load (MAX6397) 118 140
SHDN = high, (MAX6398) 104 130
SHDN = low, no load (MAX6397) 37 45
Input Supply Current
SHDN = low, (MAX6398) 11 20
µA
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 1ms
SET to GATE Propagation Delay tOV SET rising from VTH - 100mV to VTH +
100mV 0.75 µs
VOUT = VIN = 6V, RGATE to IN = 1MΩVIN +
3.8V
VIN +
4.2V
VIN +
4.6V
GATE Output High Voltage VOH
VOUT = VIN; VIN ≥ 14V, RGATE to IN = 1MΩVIN +
8.5V
VIN +
9.2V
VIN +
11.5V
V
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 1µA
Thermal Shutdown (Note 3) +150 °C
Thermal Shutdown Hysteresis 20 °C
REGULATOR (MAX6397)
IREG = 1mA 40 48
Ground Current IGND SHDN = GND IREG = 100mA 60 µA
MAX6397/MAX6398
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(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
IREG = 1mA 4.925 5 5.120
MAX6397L/M 1mA < IREG < 100mA 4.85 5.15
IREG = 1mA 3.243 3.3 3.360
MAX6397S/T 1mA < IREG < 100mA 3.201 3. 360
IREG = 1mA 2.456 2.5 2.542
MAX6397Y/Z 1mA < IREG < 100mA 2.41 2.55
V
IREG = 1mA 1.760 1.8 1.837
REG Output Voltage
(VIN ≥ VREG + 1.8V) VREG
MAX6397V/W 1mA < IREG < 100mA 1.715 1.837
5.5V ≤ VIN ≤ 72V, IREG = 1mA, VREG = 5V 0.12
Dropout Voltage (Note 4) ∆VDO 5.5V ≤ VIN ≤ 72V, IREG = 100mA, VREG = 5V 1.2
mV/V
Current Limit VIN = 14V 150 300 mA
Overvoltage-Protection Threshold VOVP 105 % of
VREG
O ver vol tag e- P r otecti on S i nk C ur r ent IOVP VREG = 1.1 x VREG (nominal) 15 mA
6.5V ≤ VIN ≤ 72V, IREG = 10mA, VREG = 5V 0.22
5.5V ≤ VIN ≤ 72V, IREG = 1mA, VREG = 5V 0.05
Line Regulation (Note 5) ∆ VREG /
∆VREG 5.5V ≤ VIN ≤ 72V, IREG = 100mA, VREG = 5V 1.5
mV/V
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
L 4.500 4.67 4.780
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
POK Assertion Threshold
(MAX6397 Only) VPOK_TH
V 1.524 1.575 1.625
V
REG to POK Delay VREG rising or falling 35 µs
POK Leakage Current VPOK = 5V 300 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
4 _______________________________________________________________________________________
Typical Operating Characteristics
(VIN = 14V, CREG = 4.7µF, IREG = 0, unless otherwise noted.)
40
60
80
100
120
140
160
02010 30 40 50 60 70 80
SUPPLY CURRENT
vs. INPUT VOLTAGE
MAX6397-98 toc01
INPUT VOLTAGE (V)
SUPPLY CURRENT (µA)
MAX6397
GATE ON
SUPPLY CURRENT vs. TEMPERATURE
MAX6397-98 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 20406080
SUPPLY CURRENT
vs. INPUT VOLTAGE
MAX6397-98 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
04020 60 80
SHUTDOWN SUPPLY CURRENT
vs. INPUT VOLTAGE (MAX6397)
MAX6397-98 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 20406080
SHUTDOWN SUPPLY CURRENT
vs. INPUT VOLTAGE
MAX6397-98 toc06
INPUT VOLTAGE (V)
SUPPLY CURRENT (µA)
MAX6398
GATE OFF
0
6
4
2
8
10
12
412106 8 14 16 18 20 22 24
GATE-DRIVE VOLTAGE
vs. INPUT VOLTAGE
MAX6397-98 toc07
INPUT VOLTAGE (V)
VGATE - VOUT (V)
VOUT = VIN
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
MAX6397-98 toc08
TEMPERATURE (°C)
VUVLO (V)
SET THRESHOLD vs. TEMPERATURE
MAX6397-98 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
_______________________________________________________________________________________
5
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
MAX6397-98 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 40608020 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 3550658095110125
REG OUTPUT VOLTAGE
vs. LOAD CURRENT AND TEMPERATURE
MAX6397-98 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
MAX6397-98 toc13
LOAD CURRENT (mA)
REG OUTPUT VOLTAGE (V)
THERMAL
SHUTDOWN
TA = +25°C
TA = +125°C
TA = -40°C
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX6397-98 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
MAX6397-98 toc16
VGATE
10V/div
VOUT
10V/div
IOUT
200mA/div
400µs/div
STARTUP WAVEFORM FROM SHUTDOWN
(CIN = 10µF, COUT = 10µF)
VSHDN
2V/div
MAX6397-98 toc17
VGATE
10V/div
VOUT
10V/div
IOUT
200mA/div
RLOAD = 100Ω
Typical Operating Characteristics (continued)
(VIN = 14V, CREG = 4.7µF, IREG = 0, unless otherwise noted.)
GATE-DRIVE VOLTAGE
vs. TEMPERATURE
MAX6397-98 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
MAX6397/MAX6398
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
6 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VIN = 14V, CREG = 4.7µF, IREG = 0, unless otherwise noted.)
200µs/div
OVERVOLTAGE SWITCH FAULT
VIN
20V/div
MAX6397-98 toc18
VGATE
20V/div
VOUT
20V/div
VREG
5V/div
VOV = 30V
1ms/div
VOLTAGE LIMIT FAULT
VIN
20V/div
MAX6397-98 toc19
VGATE
20V/div
VOUT
20V/div
VREG
5V/div
VOV = 30V
400µs/div
TRANSIENT RESPONSE
MAX6397-98 toc20
VIN
10V/div
VREG
100mV/div
CREG = 10µF
IREG = 10mA
1ms/div
REG LOAD-TRANSIENT RESPONSE
VREG
AC-COUPLED
500mV/div
MAX6397-98 toc21
IREG
100mA/div
CREG = 10µF
1ms/div
REGULATOR STARTUP WAVEFORM
VIN
10V/div
MAX6397-98 toc22
VPOK
2V/div
VREG
2V/div
IREG = 10mA
100µs/div
REGULATOR POK ASSERTION
VREG
2V/div
MAX6397-98 toc23
IREG
200mA/div
VPOK
2V/div
IREG = 0
0V
0V
0A
Detailed Description
The MAX6397/MAX6398 are ultra-small, low-current,
high-voltage protection circuits for automotive applica-
tions that must survive load dump and 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 con-
troller 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
threshold, GATE pulls to OUT, turning off
the MOSFET.
The MAX6397/MAX6398 are configurable to operate as
overvoltage protection switches or as closed-looped volt-
age limiters. In overvoltage protection switch mode, the
input voltage is monitored. When an overvoltage condi-
tion 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 voltage 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-low 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.
MAX6397/MAX6398
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
_______________________________________________________________________________________ 7
Pin Description
PIN
MAX6397 MAX6398 NAME FUNCTION
1 1 IN Supply Voltage Input. Bypass with a minimum 10µF capacitor to GND.
22SHDN
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
The MAX6397 integrates a high-input-voltage, low-qui-
escent-current linear regulator in addition to an over-
voltage 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 stan-
dard output voltage options (5V, 3.3V, 2.5V, or 1.8V).
An open-drain power-good output notifies the system if
the regulator output falls to 92.5% or 87.5% of its nomi-
nal voltage. The MAX6397’s REG output operates inde-
pendently of the SHDN logic input.
The MAX6397/MAX6398 include internal thermal-shut-
down protection, disabling the external MOSFET and
linear regulator if the chip reaches overtemperature
conditions.
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 100kΩrange 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 overvolt-
age switch modes are quite similar but have distinct
characteristics. In overvoltage switch mode (Figure 2a),
GATE is enhanced to VIN + 10V while the monitored IN
voltage remains below the overvoltage fault threshold
(SET < 1.215V). When an overvoltage fault occurs (SET
≥1.215V), GATE is pulled one diode below OUT, turn-
ing 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% hys-
teresis) GATE is again enhanced to VIN + 10V.
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.
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
8 _______________________________________________________________________________________
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
Figure 1. Functional Diagram
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 over-
voltage limiter’s sawtooth GATE output operates the
MOSFET in a switched-linear mode while the input volt-
age 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 over-
voltage threshold is tripped, the internal fast compara-
tor turns off the external MOSFET, pulling GATE to OUT
within tOV and disconnecting the power source from
the load. When IN decreases below the adjusted over-
voltage 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, dis-
charging the external GATE, regulating OUT at the set
overvoltage threshold. OUT remains active during the
overvoltage transients and the MOSFET continues to con-
duct during the overvoltage event, operating in switched-
linear mode.
MAX6397/MAX6398
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
_______________________________________________________________________________________ 9
VGATE
10V/div
VOUT
10V/div
VIN
10V/div
10ms/div
Figure 2a. MAX6397/MAX6398 GATE Waveform During Over-
voltage Switch Mode
VGATE
10V/div
VOUT
10V/div
VIN
10V/div
4ms/div
Figure 2b. MAX6397/MAX6398 GATE Waveform During Over-
voltage Limit Mode
MAX6397
MAX6398
IN
SET
GATE
OUT
GND
VBATT
R1
R2
Figure 3. Overvoltage Switch Protection Configuration
MAX6397/MAX6398
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 capaci-
tance. 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
Load Dump
Most automotive applications run off a multicell, 12V
lead-acid battery with a nominal voltage that swings
between 9V and 16V (depending on load current,
charging status, temperature, battery age, etc.). The
battery voltage is distributed throughout the automobile
and is locally regulated down to voltages required by
the different system modules. Load dump occurs when
the alternator is charging the battery and the battery
becomes disconnected. Power in the alternator (essen-
tially an inductor) flows into the distributed power sys-
tem and elevates the voltage seen at each module. The
voltage spikes have rise times typically greater than
5ms and decays within several hundred milliseconds
but can extend out to 1s or more depending on the
characteristics of the charging system (Figure 5).
These transients are capable of destroying semicon-
ductors on the first ‘fault event.’
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 6). 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 cur-
rent 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 calculate R2:
where VTH is the 1.215V SET rising threshold and VOV
is the overvoltage threshold.
R2 = 243kΩ, use a 240kΩstandard resistor.
RTOTAL = R2 + R1, where R1 = 3.76MΩ.
Use a 3.79MΩstandard resistor.
A lower value for total resistance dissipates more
power but provides slightly better accuracy.
RV R
V
TH TOTAL
OV
2 =×
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
10 ______________________________________________________________________________________
MAX6397
MAX6398
IN
SET
GATE
OUT
GND
VBATT
R1
R2
COUT
Figure 4. Overvoltage Limiter Protection Switch Configuration
100ms 200ms 300ms 400ms
tRISE > 5ms
VPEAK
VBATT
Figure 5. Load Dump Voltage Profile
Reverse-Battery Protection
Use a diode or p-channel MOSFET to protect the
MAX6397/MAX6398 during a reverse-battery insertion
(Figures 7a, 7b). Low p-channel MOSFET on-resistance
of 30mΩor less yields a forward-voltage drop of only a
few millivolts (versus hundreds of millivolts for a diode,
Figure 7a) thus improving efficiency.
Connecting a positive battery voltage to the drain of Q1
(Figure 7b) 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 bat-
tery from the system. The zener diode and resistor com-
bination prevent damage to the p-channel MOSFET
during an overvoltage condition.
MAX6397/MAX6398
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
______________________________________________________________________________________ 11
MAX6397
MAX6398
IN
SET
GATE
OUT
GND
IN
R1
R2
MAX6397
MAX6398
IN
SET
GATE
OUT
GND
R1
R2
IN
Figure 6. Setting the MAX6397/MAX6398 Overvoltage Threshold
MAX6397
MAX6398
LOAD
(b)
VBATT
Q1
GND
IN
OUT
GATE
MAX6397
MAX6398
LOAD
(a)
VBATT
GND
IN
OUT
GATE
Figure 7. Reverse Battery Protection Using a Diode or p-Channel MOSFET
MAX6397/MAX6398
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 nec-
essary to increase capacitance.
Under normal conditions, use a 10µF capacitor at IN.
Larger input capacitor values and lower ESR provide bet-
ter supply-noise rejection and line-transient response.
Inrush/Slew-Rate Control
Inrush current control can be implemented by placing a
capacitor at GATE (Figure 8) to slowly ramp up the
GATE, thus limiting the inrush current and controlling
GATE’s slew rate during initial turn-on. The inrush cur-
rent can be approximated using the following formula:
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 over-
voltage 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 9).
Add a resistor in series with IN to limit transient current
going into the input for the MAX6398 only.
IC
CII
INRUSH OUT
GATE GATE LOAD
=×+
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
12 ______________________________________________________________________________________
MAX6397
MAX6398
LOAD
VBATT
GND
IN
OUT
GATE
CGATE COUT
Figure 8. MAX6397/MAX6398 Controlling GATE Inrush Current
MAX6397
MAX6398
LOAD
GND
IN
OUT
GATE
VBATT
60V
TVS
1kΩ
Figure 9. Protecting the MAX6397/MAX6398 Input from High-
Voltage Transients
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.
During normal operation, the external MOSFETs dissipate
little power. The power dissipated in normal operation is:
PQ1 = ILOAD2x RDS(ON).
The most power dissipation will occur during a pro-
longed overvoltage event when operating the
MAX6397/MAX6398 in voltage limiter mode, resulting in
high power dissipated in Q1 (Figure 10) 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 MAX6397/MAX6398 thermal-shutdown feature shuts
off the linear regulator output, REG, and GATE if it
exceeds the maximum allowable thermal dissipation.
Thermal shutdown also monitors the PC board tempera-
ture 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 cur-
rent-limit fault conditions. For continuous operation, do
not exceed the absolute maximum junction-tempera-
ture rating of TJ= +150°C.
Thermal Shutdown
Overvoltage Limiter Mode
When operating the MAX6397/MAX6398 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 differ-
ent 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)
MAX6397/MAX6398
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
______________________________________________________________________________________ 13
MAX6397
MAX6398
LOAD
GND
IN
OUT
GATE
VBATT
60V
TVS
SET
VQ1
+-
ILOAD
VBATT
VMAX
VOV
Figure 10. Power Dissipated Across MOSFETs During an
Overvoltage Fault (Overvoltage Limiter Mode)
t2
t1t3
tOVP
GATE
OUT
Figure 11. MAX6397/MAX6398 Timing Diagram
MAX6397/MAX6398
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:
where VOV is the adjusted overvoltage threshold, IOUT
is the external load current and IGATEPD is the GATE’s
internal 100mA (typ) pulldown current.
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 volt-
age 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:
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 cur-
rent (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:
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 approxi-
mated using the following formula:
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 dur-
ing an overvoltage event when IOUT = 0 (COUT is dis-
charged only by the internal current sink). The maximum
power dissipation can be approximated using the follow-
ing equation:
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 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 pro-
tection 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 12 illustrates the junction temperature
vs. output capacitor with IOUT = 0, TA= +125°C,
VOV < 16V,VF= 1.5V, IGATE = 75mA, and IGATEPD =
100mA. Figure 12 shows the relationship between output
capacitance versus die temperature for the conditions
listed above.
PV I t
t
DISS OV GATEPD OVP
. =× × ×0 975 1∆
∆
∆∆
tQ
V
V
I
GD
GS QGD
OUT
GATE
3
_
≅×
∆∆
VI t
C
OUT OUT
22
=
∆tC
VV
I
ISS
GS TH F
GATE
2
()
=+
∆tC V
II
OUT OV
OUT GATEPD
1005
.
=×
+
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
14 ______________________________________________________________________________________
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
Figure 12. Junction Temperature vs. COUT
An additional capacitor can be added to GATE and
GND to shift the curves as this increases ∆t1. These val-
ues 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 dissi-
pation limits the amount of output current available for a
given input/output voltage and ambient temperature.
Figure 13 depicts the maximum power dissipation curve
for the MAX6397. The graph assumes that the exposed
metal pad of the MAX6397 package is soldered to 1in2of
PC board copper. Use Figure 11 to determine the allow-
able package dissipation for a given ambient tempera-
ture. 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 follow-
ing formula:
IP
VV mA
OUT MAX DISS
IN REG
()
=≤
−100
MAX6397/MAX6398
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
______________________________________________________________________________________ 15
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
Figure 13. Maximum Power Dissipation vs. Temperature
MAX6397
GATE
POK
REG
IN
SHDN GND
SET
OUT
ALWAYS-ON
µC
VCC
RESET
GPIO
12V IN
DC-DC
CONVERTER
OUTIN
GND
µC
Typical Application Circuit
MAX6397/MAX6398
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
16 ______________________________________________________________________________________
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
Typical Operating Circuit
6
GATE
5
OUT
4
SET
12
GND
3
SHDN
MAX6398
IN
TDFN
TOP VIEW
*EP
*EXPOSED PAD. CONNECT TO GND.
Pin Configurations (continued) Selector Guide
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
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
______________________________________________________________________________________ 17
Chip Information
TRANSISTOR COUNT: 590
PROCESS: BiCMOS
Package Information
For the latest package outline information and land patterns, go
to www.maxim-ic.com/packages.
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
6 TDFN T633-2 21-0137
8 TDFN T833-2 21-0137
MAX6397/MAX6398
Overvoltage Protection Switch/Limiter
Controllers Operate Up to 72V
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.
18
____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2009 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
Revision History
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
