General Description
The MAX6495–MAX6499 is a family of small, low-cur-
rent, overvoltage-protection circuits for high-voltage
transient systems such as those found in automotive
and industrial applications. These devices monitor the
input voltage and control an external n-channel MOSFET
switch to isolate the load at the output during an input
overvoltage condition. The MAX6495–MAX6499 operate
over a wide supply voltage range from +5.5V to +72V.
The gate of the n-channel MOSFET is driven high while
the monitored input is below the user-adjustable over-
voltage threshold. An integrated charge-pump circuit
provides a 10V gate-to-source voltage to fully enhance
the n-channel MOSFET. When the input voltage
exceeds the user-adjusted overvoltage threshold, the
gate of the MOSFET is quickly pulled low, disconnect-
ing the load from the input. In some applications, dis-
connecting 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 saw-
tooths to limit the voltage to the load (MAX6495/
MAX6496/MAX6499).
The MAX6496 supports lower input voltages and
reduces power loss by replacing the external reverse
battery diode with an external series p-channel MOSFET.
The MAX6496 generates the proper bias voltage to
ensure that the p-channel MOSFET is on during normal
operations. The gate-to-source voltage is clamped dur-
ing load-dump conditions, and the p-channel MOSFET
is off during reverse-battery conditions.
The MAX6497/MAX6498 feature an open-drain, undedi-
cated comparator that notifies the system if the output
falls below the programmed threshold. The MAX6497
keeps the MOSFET switch latched off until either the
input power or the SHDN pin is cycled. The MAX6498
will autoretry when VOVSET falls below 130mV.
These devices are available in small, thermally
enhanced, 6-pin and 8-pin TDFN packages and are
fully specified from -40°C to +125°C.
Applications
Automotive
Industrial
Telecom/Servers/Networking
FireWire®
Notebook Computers
Features
oWide Supply Voltage Range: +5.5V to +72V
oOvervoltage-Protection Switch Controller Allows
User to Size External n-Channel MOSFETs
oFast Gate Shutoff During Overvoltage with 100mA
Sink Capability
oInternal Charge-Pump Circuit Ensures 10V
Gate-to-Source Enhancement for Low RDS(ON)
Performance
on-Channel MOSFET Latches Off After an
Overvoltage Condition (MAX6497/MAX6499)
oAdjustable Overvoltage Threshold
oThermal Shutdown Protection
oSupports Series p-Channel MOSFET for Reverse-
Battery Voltage Protection (MAX6496)
oPOK Indicator (MAX6497/MAX6498)
oAdjustable Undervoltage Threshold (MAX6499)
o-40°C to +125°C Operating Temperature Range
oSmall, 3mm x 3mm TDFN Package
MAX6495–MAX6499
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
12 3
65 4
IN SHDN OVSET
OUTFB GATE GND
MAX6495
3mm x 3mm TDFN
TOP VIEW
Pin Configurations
Ordering Information
19-3778; Rev 10; 6/12
1
For pricing, delivery, and ordering information, please contact Maxim Direct
at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Ordering Information continued at end of data sheet.
Note: All devices are specified over the -40°C to +125°C operating
temperature range.
+
Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
*
EP = Exposed pad.
/
V denotes an automotive qualified part.
Selector Guide appears at end of data sheet.
EVALUATION KIT
AVAILABLE
FireWire is a registered trademark of Apple, Inc.
PART PIN-PACKAGE TOP MARK
MAX6495ATT+T 6 TDFN-EP* AJM
MAX6495ATT/V+T 6 TDFN-EP* AUG
Pin Configurations continued at end of data sheet.
MAX6495–MAX6499
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
2
ABSOLUTE MAXIMUM RATINGS
(All pins referenced to GND.)
ELECTRICAL CHARACTERISTICS
(VIN = 14V, CGATE = 6nF, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA= +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
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
IN, GATE, GATEP ...................................................-0.3V to +80V
SHDN, CLEAR .............................................-0.3V to (VIN + 0.3V)
POK, OUTFB ..........................................................-0.3V to +80V
GATE to OUTFB .....................................................-0.3V to +12V
GATEP to IN ...........................................................-12V to +0.3V
OVSET, UVSET, POKSET .......................................-0.3V to +12V
Current Sink/Source (All Pins).............................................50mA
All Other Pins to GND ..................................-0.3V to (VIN + 0.3V)
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 .........................-40°C to +125°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-60°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Soldering Temperature (reflow) .......................................+260°C
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Supply Voltage Range VIN 5.5 72.0 V
SHDN = high 100 150
SHDN = low (MAX6497/MAX6498/
MAX6499) 15 24
Input Supply Current IIN No load
SHDN = low (MAX6495/MAX6496) 24 32
µA
IN Undervoltage Lockout VIN rising, enables GATE 4.75 5 5.25 V
IN Undervoltage Lockout
Hysteresis VIN falling, disables GATE 155 mV
VTH+ OVSET rising 1.22 1.24 1.26
OVSET Threshold Voltage
(MAX6495/MAX6496) VTH- OVSET falling 1.18 V
OVSET Threshold Hysteresis
(MAX6495/MAX6496) VHYST OVSET falling 5 %
VTH+ OVSET rising 0.494 0.505 0.518
OVSET Threshold Voltage
(MAX6497/MAX6498) VTH- OVSET falling 0.13 V
VTH+ OVSET rising 1.22 1.24 1.26
OVSET Threshold Voltage
(MAX6499) VTH- OVSET falling 1.18 V
VTH+ UVSET rising 1.22 1.24 1.26
UVSET Threshold Voltage
(MAX6499) VTH- UVSET falling 1.18 V
OVSET/UVSET Threshold
Hysteresis (MAX6499) VHYST OVSET falling 5 %
VPOKSET+ POKSET rising 1.22 1.24 1.26
POKSET Threshold Voltage
(MAX6497/MAX6498) VPOKSET- POKSET falling 1.18 V
POKSET Threshold
Hysteresis (MAX6497/
MAX6498)
VHYST POKSET falling 5 %
OVSET, UVSET, POKSET
Input Current ISET -50 +50 nA
Startup Response Time tSTART SHDN rising (Note 2) 100 µs
GATE Rise Time GATE rising from GND to VOUTFB + 8V,
OUTFB = GND 1ms
MAX6495–MAX6499
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
3
Note 1: Specifications to TA= -40°C are guaranteed by design and not production tested.
Note 2: The MAX6495–MAX6499 power up with the external MOSFET in off mode (VGATE = GND). The external MOSFET turns on
tSTART after all input conditions are valid.
Note 3: For accurate overtemperature-shutdown performance, place the device in close thermal contact with the external MOSFET.
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 14V, CGATE = 6nF, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
OVSET to GATE Propagation
Delay tOV SET rising from VTH - 100mV to VTH + 100mV 0.6 µs
UVSET to GATE, POKSET to
POK Propagation Delay
POKSET, UVSET falling from VTH + 100mV to
VTH - 100mV 20 µs
VOUTFB = VIN = 5.5V, RGATE to IN = 1MΩVIN + 3.4 VIN + 3.8 VIN + 4.2
GATE Output High Voltage VOH VOUTFB = VIN
,
VIN ≥ 14V, RGATE to IN = 1MΩVIN + 8 VIN + 10 VIN + 11 V
GATE sinking 15mA, OUTFB = GND 1
GATE Output Low Voltage VOL VIN = 5.5V, GATE sinking 1mA, OUTFB = GND 0.9 V
GATE Charge-Pump Current IGATE GATE = GND 100 µA
GATE to OUTFB Clamp
Voltage VCLMP 12 18 V
IN to GATEP Output Low
Voltage IGATEP_SINK = 75µA, IGATEP_SOURCE = 1µA 7.5 11.7 V
IN to GATEP Clamp Voltage VIN = 24V, IGATEP_SOURCE = 10µA 12 18 V
SHDN, CLEAR Logic-High
Input Voltage VIH 1.4
SHDN, CLEAR Logic-Low
Input Voltage VIL 0.4
V
SHDN Input Pulse Width 7µs
CLEAR Input Pulse Width 0.5 µs
SHDN, CLEAR Input
Pulldown Current SHDN is Internally pulled down to GND 0.6 1.0 1.4 µA
Thermal Shutdown (Note 3) +160 °C
Thermal-Shutdown
Hysteresis 20 °C
POKSET to POK Delay
(MAX6497/MAX6498) 35 µs
VIN ≥ 14V, POKSET = GND, ISINK = 3.2mA 0.4
POK Output Low Voltage
(MAX6497/MAX6498) VOL VIN ≥ 2.8V, POKSET = GND, ISINK = 100µA 0.4 V
POK Leakage Current
(MAX6497/MAX6498) VPOKSET = 14V 100 nA
MAX6495–MAX6499
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
4
Typical Operating Characteristics
(VIN = +12V, TA= +25°C, unless otherwise noted.)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6495 toc01
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (µA)
655545352515
35
60
85
110
135
10
575
SET = GND, GATE ENHANCED
SUPPLY CURRENT vs. TEMPERATURE
MAX6495 toc02
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
11095-25 -10 535 50 6520 80
102.5
105.0
107.5
110.0
112.5
115.0
117.5
120.0
100.0
-40 125
SET = GND, GATE ENHANCED
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6495 toc03
SUPPLY VOLTAGE (V)
SHUTDOWN SUPPLY CURRENT (µA)
655545352515
20
30
40
50
10
575
SET = GND, SHDN = GND
MAX6496
GATE VOLTAGE vs. SUPPLY VOLTAGE
MAX6495 toc04
SUPPLY VOLTAGE (V)
VGATE - VIN (V)
655545352515
3
6
9
12
0
575
SET = GND, IN = OUTFB = SHDN
GATEP VOLTAGE vs. SUPPLY VOLTAGE
MAX6495 toc05
SUPPLY VOLTAGE (V)
VIN - VGATEP (V)
655545352515
3
6
9
12
0
575
SET = GND, IN = OUTFB = SHDN
UVLO THRESHOLD vs. TEMPERATURE
MAX6495 toc06
TEMPERATURE (°C)
UVLO THRESHOLD (V)
1109565 80-10 5 20 35 50-25
4.6
4.7
4.8
4.9
5.0
5.1
5.2
5.3
5.4
5.5
4.5
-40 125
SET = GND, IN = OUTFB = SHDN
FALLING
RISING
SET THRESHOLD vs. TEMPERATURE
MAX6495 toc07
TEMPERATURE (°C)
SET THRESHOLD (V)
1109580655035205-10-25
1.15
1.20
1.25
1.30
1.35
1.40
1.10
-40 125
IN = SHDN
FALLING
RISING
GATE TO OUTFB CLAMP VOLTAGE
vs. TEMPERATURE
MAX6495 toc08
TEMPERATURE (°C)
VGATE - VOUTFB (V)
1109565 80-10 520 35 50-25
15.6
15.7
15.8
15.9
16.0
16.1
16.2
16.3
16.4
16.5
15.5
-40 125
SET = OUTFB = GND
IN = SHDN
MAX6495–MAX6499
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
5
STARTUP WAVEFORM
(CIN = 100µF, COUT = 10µF, ROUT = 100Ω)
MAX6495 toc09
400µs/div
VIN
10V/div
VGATE
10V/div
VOUT
10V/div
OVERVOLTAGE SWITCH FAULT
(CIN = 100µF, COUT = 10µF, ROUT = 100Ω)
MAX6495 toc11
200µs/div
VIN
20V/div
VGATE
20V/div
VOUT
20V/div
OVERVOLTAGE LIMITER
(CIN = 100µF, COUT = 10µF, ROUT = 100Ω)
MAX6495 toc12
400µs/div
VIN
20V/div
VGATE
20V/div
VOUT
20V/div
TRIP THRESHOLD = 28V
Typical Operating Characteristics (continued)
(VIN = +12V, TA= +25°C, unless otherwise noted.)
MAX6495–MAX6499
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
6
Pin Description
PIN
MAX6495
MAX6496
MAX6497/MAX6498
MAX6499
NAME FUNCTION
1111 IN
Positive Supply Voltage. Connect IN to the positive side of the input voltage. Bypass IN
with a 10µF capacitor to GND.
2222SHDN
Shutdown Input. Drive SHDN low to force GATE low and turn off the external n-channel
MOSFET. Drive SHDN low and then high to reset the overvoltage-condition latch. SHDN
is internally pulled to GND with 1µA of current. Connect SHDN to IN for normal operation.
3333
OVSET
Overvoltage-Threshold Adjustment Input. Connect OVSET to an external resistive
voltage-divider network to adjust the desired overvoltage-disable or overvoltage-limit
threshold. Connect the resistor network to the input side (drain) of the n-channel
MOSFET for overvoltage switch turn-off applications or to the output side (source) of the
n-channel MOSFET for overvoltage-limiting applications (MAX6495/MAX6496/MAX6499).
4 5 5 5 GND Ground
5 6 6 6 GATE
Gate-Driver Output. Connect GATE to the gate of the external n-channel MOSFET switch.
GATE is the output of a charge pump with a 100µA pullup current to 10V (typ) above IN
during normal operation. GATE is quickly clamped to OUTFB during an overvoltage
condition. GATE pulls low when SHDN is low.
6777
OUTFB
Output-Voltage-Sense Input. Connect OUTFB to the source of the external n-channel
MOSFET switch.
—
4
— — GATEP
p-Channel Gate-Driver Output. Connect GATEP to the gate of an external p-channel
MOSFET to provide low-drop reverse-voltage protection. GATEP is biased to ensure that
the p-channel MOSFET is on during normal operating modes, the gate-to-source is not
overstressed during load-dump/overvoltage conditions, and the p-channel MOSFET is
off during reverse-battery conditions.
—
8
——
N.C. No Connection. Not internally connected.
—
—
4
—
POK
Power-OK Output. POK is an open-drain output. POK remains low while POKSET is
below the internal POKSET threshold. POK goes high impedance when POKSET goes
above the internal POKSET threshold. Connect POK to an external pullup resistor.
—
—
8
— POKSET
Power-OK Threshold-Adjustment Input. POK remains low while POKSET is below the
internal POKSET threshold (1.18V). POK goes high impedance when POKSET goes
above the internal POKSET threshold (1.24V). Connect a resistive divider from OUTFB
to POKSET to adjust the desired undervoltage threshold.
—
——
4
CLEAR
Latch Clear Input. Connect CLEAR to a logic-high to latch the device off after an
overvoltage condition. With OVSET below VTH, pulse CLEAR low (5µs typ)
to reset the output latch. Connect CLEAR to GND to make the latch transparent.
—
——
8
UVSET
Undervoltage-Threshold Adjustment Input. Connect UVSET to an external resistive
voltage-divider network to adjust the desired undervoltage threshold.
—
———
EP
Exposed Pad. EP is internally connected to GND. Connect EP to the ground plane to
provide a low thermal-resistance path from the IC junction to the PC board. Do not use
as the primary electrical connection to GND.
Detailed Description
Overvoltage Monitoring
When operating in overvoltage mode, the MAX6495–
MAX6499 feedback path (Figure 1) consists of IN,
OVSET’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, clamping GATE to
OUTFB within 0.5µs and disconnecting the power
source from the load. When IN decreases below the
adjusted overvoltage threshold, the MAX6495–MAX6499
slowly enhance GATE above OUTFB, reconnecting the
load to the power source.
Overvoltage Limiter
(MAX6495/MAX6496/MAX6499)
When operating in overvoltage-limiter mode, the
MAX6495/MAX6496/MAX6499 feedback path (Figure 2)
consists of OUTFB, OVSET’s internal comparator, the
internal gate charge pump, and the external n-channel
MOSFET, resulting in the external MOSFET operating
as a voltage regulator.
During normal operation, GATE is enhanced 10V above
OUTFB. The external MOSFET source voltage is moni-
tored through a resistive divider between OUTFB and
OVSET. When OUTFB rises above the adjusted over-
voltage threshold, an internal comparator sinks the
charge-pump current, discharging the external GATE,
regulating OUTFB at the OVSET overvoltage threshold.
OUTFB remains active during the overvoltage transients
and the MOSFET continues to conduct during the over-
voltage event, operating in switched-linear mode.
As the transient begins decreasing, OUTFB fall time will
depend on the MOSFET’s GATE charge, the internal
charge-pump current, the output load, and the tank
capacitor at OUTFB.
For fast-rising transients and very large-sized MOSFETs,
add an additional 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 MOSFET’s drain-to-gate capacitance. For a
6000pF gate-to-source capacitance, a 0.1µF capacitor at
GATE will reduce the impact of the fast-rising VIN input.
Caution must be exercised when operating the
MAX6495/MAX6496/MAX6499 in voltage-limiting mode
for long durations. If the VIN is a DC voltage greater than
the MOSFET’s maximum gate voltage, the MOSFET dis-
sipates power continuously. To prevent damage to the
external MOSFET, proper heatsinking should be imple-
mented.
GATE Voltage
The MAX6495–MAX6499 use a high-efficiency charge
pump to generate the GATE voltage. Upon VIN exceed-
ing the 5V (typ) UVLO threshold, GATE enhances 10V
above VIN (for VIN ≥14V) with a 100µA pullup current.
An overvoltage condition occurs when the voltage at
OVSET goes above its VTH+ threshold. When the
threshold is crossed, GATE falls to OUTFB within 0.5µs
with a 100mA pulldown current. The MAX6495–MAX6499
include an internal clamp to OUTFB that ensures GATE
is limited to 18V (max) above OUTFB to prevent gate-
to-source damage of the external MOSFET.
MAX6495–MAX6499
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
7
OVSET
GND
GATE
IN OUTFB
R1
VIN VOUT
R2
MAX6495–
MAX6499
Figure 1. Overvoltage Threshold (MAX6495–MAX6499)
OVSET
GND
GATE
IN OUTFB
R1
COUT
VIN VOUT
R2
MAX6495
MAX6496
MAX6499
Figure 2. Overvoltage-Limiter Protection Switch Configuration
MAX6495–MAX6499
The gate cycles during overvoltage-limit and overvolt-
age-switch modes are quite similar but have distinct
characteristics. In overvoltage-switch mode, GATE is
enhanced to (VIN + 10V) while the monitored VIN volt-
age remains below the overvoltage fault threshold
(OVSET < VTH+). When an overvoltage fault occurs
(OVSET ≥VTH+), GATE is pulled one diode drop below
OUTFB, turning off the external MOSFET and discon-
necting the load from the input. GATE remains low
(MOSFET off) as long as the VIN voltage is above the
overvoltage fault threshold. As VIN falls back below the
overvoltage fault threshold, GATE is again enhanced to
(VIN + 10V).
In overvoltage-limit mode, GATE is enhanced to (VIN
+10V) while the monitored OUTFB voltage remains
below the overvoltage fault threshold (OVSET < VTH+).
When an overvoltage fault occurs (OVSET ≥VTH+),
GATE is pulled one diode drop below OUTFB until
OUTFB drops 5% below the overvoltage fault threshold
(MAX6495/MAX6496/MAX6499). GATE is then turned
back on until OUTFB reaches the overvoltage fault
threshold and GATE is again turned off. GATE cycles in
a sawtooth waveform until OUTFB remains below the
overvoltage fault threshold and GATE remains con-
stantly on (VIN +10V). The overvoltage limiter’s saw-
tooth GATE output operates the MOSFET in a
switched-linear mode while the input voltage remains
above the overvoltage fault threshold. The sawtooth fre-
quency 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.
Undervoltage Monitoring (MAX6499)
The MAX6499 includes undervoltage and overvoltage
comparators for window detection (see Figures 3 and
12). GATE is enhanced and the n-channel MOSFET is
on when the monitored voltage is within the selected
“window.” When the monitored voltage falls below the
lower limit (VTRIPLOW) or exceeds the upper limit
(VTRIPHIGH) of the window, GATE falls to OUTFB turn-
ing off the MOSFET. The application in Figure 3 shows
the MAX6499 enabling the DC-DC converter when the
monitored voltage is in the selected window.
The resistor values R1, R2, and R3 can be calculated
as follows:
where RTOTAL = R1 + R2 + R3.
Use the following steps to determine the values for R1,
R2, and R3:
1) Choose a value for RTOTAL, the sum of R1, R2, and
R3. Because the MAX6499 has very high input
impedance, RTOTAL can be up to 5MΩ.
2) Calculate R3 based on RTOTAL and the desired
upper trip point:
3) Calculate R2 based on RTOTAL, R3, and the desired
lower trip point:
4) Calculate R1 based on RTOTAL, R2, and R3:
R1 = RTOTAL – R2 – R3
To improve ESD protection, keep R3 ≥1kΩ.
RVR
VR
TH TOTAL
TRIPLOW
23 =
()
×
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥−
−
RVR
V
TH TOTAL
TRIPHIGH
3
=×
+
VV
R
RR
VV
R
R
TRIPLOW TH TOTAL
TRIPHIGH TH TOTAL
=
()
+
⎛
⎝
⎜⎞
⎠
⎟
=
()
⎛
⎝
⎜⎞
⎠
⎟
−
+
23
3
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
8
OVSET
GND
CLEAR
GATE OUTFB
IN
SHDN
UVSET
R2
VIN
R3
R1
MAX6499
DC-DC
CONVERTER
GND
IN OUT
Figure 3. MAX6499 Window-Detector Circuit
Power-OK Output (MAX6497/MAX6498)
POK is an open-drain output that remains low when the
voltage at POKSET is below the internal POKSET
threshold (1.18V). POK goes high impedance when
POKSET goes above the internal POKSET threshold
(1.24V). Connect a resistive divider from OUTFB to
POKSET to adjust the desired undervoltage threshold.
Use a resistor in the 100kΩrange from POKSET to
GND to minimize current consumption.
Overvoltage Latch Function
The MAX6497/MAX6499 offers a latch function that pre-
vents the external MOSFET from turning on until the
latch is cleared. For the MAX6497, the latch can be
cleared by cycling the power on the input IN to a volt-
age below the undervoltage lockout or by pulling the
shutdown input low and then back to a logic-high
state. The MAX6499 offers a CLEAR input that latches
the n-MOSFET off when CLEAR is high. The latch is
removed when the CLEAR input is plused low. Connect
CLEAR low to make the latch transparent.
Overvoltage Retry Function
The MAX6498 offers an automatic retry function that
tries to enhance the external n-channel MOSFET after
the overvoltage condition is removed. When the monitored
input voltage detects an overvoltage condition (VSET >
VTH+), the n-MOSFET is turned off. The MOSFET stays off
until the voltage at VSET falls below its VTH- (typically
0.13V), at which point the output tries to turn on again.
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. The alternator voltage regula-
tor is temporarily driven out of control. Power from the
alternator flows into the distributed power system 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 characteris-
tics of the charging system. These transients are capa-
ble of destroying sensitive electronic equipment on the
first “fault event.”
Setting Overvoltage Thresholds
OVSET provides an accurate means to set the overvolt-
age level for the MAX6495–MAX6499. Use a resistive
divider to set the desired overvoltage condition (see
Figure 2). OVSET has a rising 1.24V threshold with a
5% falling hysteresis (MAX6495/MAX6496/MAX6499)
and a rising 0.505V threshold with a falling 0.15V
threshold (MAX6497/MAX6498).
Begin by selecting the total end-to-end resistance, RTO-
TAL = R1 + R2. Choose RTOTAL to yield a total current
equivalent to a minimum 100 x ISET (OVSET’s input bias
current) at the desired overvoltage threshold.
For example:
With an overvoltage threshold (VOV) set to 20V for the
MAX6495/MAX6496/MAX6499, RTOTAL < 20V / (100 x
ISET), where ISET is OVSET’s 50nA (max) input bias current.
RTOTAL < 4MΩ
Use the following formula to calculate R2:
where VTH+ is the 1.24V OVSET rising threshold and
VOV is the desired overvoltage threshold.
R2 = 248kΩ. Use a 249kΩstandard resistor.
RTOTAL = R2 + R1, where R1 = 3.751MΩ. Use a
3.74MΩstandard resistor.
A lower value for total resistance dissipates more power
but provides slightly better accuracy. To improve ESD
protection, keep R2 ≥1kΩ.
Reverse-Battery Protection
The MAX6496 is an overvoltage-protection circuit that is
capable of driving a p-channel MOSFET to prevent
reverse-battery conditions. This MOSFET eliminates the
need for external diodes, thus minimizing the input volt-
age drop (see Figure 8).
Inrush/Slew-Rate Control
Inrush current control can be implemented by placing a
capacitor from GATE to GND 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 equation:
IC
CII
INRUSH OUT
GATE GATE LOAD
=×+
RV R
V
TH TOTAL
OV
2 =×
+
MAX6495–MAX6499
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
9
MAX6495–MAX6499
where IGATE is GATE’s 100µA sourcing current, ILOAD
is the load current at startup, and COUT is the output
capacitor.
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 a minimum volt-
age drop at full load to limit the MOSFET power dissipa-
tion. Determine the device power rating to
accommodate an overvoltage fault when operating the
MAX6495/MAX6496/MAX6499 in overvoltage-limit mode.
During normal operation, the external MOSFET dissi-
pates little power. The power dissipated in the MOSFET
during normal operation is:
P= I
LOAD2x RDS(ON)
where P is the power dissipated in the MOSFET, ILOAD
is the output load current, and RDS(ON) is the drain-to-
source resistance of the MOSFET.
Most power dissipation in the MOSFET occurs during a
prolonged overvoltage event when operating the
MAX6495/MAX6496/MAX6499 in voltage-limiter mode.
The power dissipated across the MOSFET is as follows
(see the
Thermal Shutdown in Overvoltage-Limiter
Mode
section):
P = VDS x ILOAD
where VDS is the voltage across the MOSFET’s drain
and source.
Thermal Shutdown
The MAX6495–MAX6499 thermal-shutdown feature
turns off GATE if it exceeds the maximum allowable
thermal dissipation. Thermal shutdown also monitors
the PC board temperature of the external n-channel
MOSFET when the devices sit on the same thermal
island. Good thermal contact between the MAX6495–
MAX6499 and the external n-channel MOSFET is essen-
tial for the thermal-shutdown feature to operate effec-
tively. Place the n-channel MOSFET as close to
possible to OUTFB.
When the junction temperature exceeds TJ= +160°C,
the thermal sensor signals the shutdown logic, turning
off the GATE output and allowing the device to cool.
The thermal sensor turns the GATE on again after the
IC’s junction temperature cools by 20°C. Thermal-over-
load protection is designed to protect the MAX6495–
MAX6499 and the external MOSFET in the event of cur-
rent-limit fault conditions. For continuous operation, do
not exceed the absolute maximum junction-temperature
rating of TJ= +150°C.
Peak Power-Dissipation Limit
The MAX6495–MAX6499 activate an internal 100mA
pulldown on GATE when SHDN goes low, OVSET
exceeds its threshold or UVSET falls below its threshold.
Once the voltage on GATE falls below the OUTFB volt-
age, current begins to flow from OUTFB to the 100mA
pulldown through the internal clamp diode, discharging
the output capacitors.
Depending on the output capacitance and the initial volt-
age, a significant amount of energy may be dissipated
by the internal 100mA pulldown. To prevent damage to
the device ensure that for a given overvoltage threshold,
the output capacitance does not exceed the limit provid-
ed in Figure 4. This output capacitance represents the
sum of all capacitors connected to OUTFB, including
reservoir capacitors and DC-DC input filter capacitors.
Thermal Shutdown in Overvoltage-Limiter Mode
When operating the MAX6495/MAX6496/MAX6499 in
overvoltage-limit mode for a prolonged period of time, a
thermal shutdown is possible. The thermal shutdown is
dependent on a number of different factors:
• The device’s ambient temperature
• The output capacitor (COUT)
• The output load current (IOUT)
• The overvoltage threshold limit (VOV)
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
10
MAXIMUM OUTPUT CAPACITANCE
vs. OVERVOLTAGE THRESHOLD
MAX6495 fig04
OVERVOLTAGE THRESHOLD (V)
MAXIMUM OUTPUT CAPACITANCE (µF)
605040302010
100
1000
10,000
100,000
10
070
SAFE OPERATING AREA
Figure 4. Safe Operating Area for 100mA Pulldown.
• The overvoltage waveform period (tOV)
• The power dissipated across the package (PDISS)
During an initial overvoltage occurrence, the discharge
time (∆t1) of COUT, caused by IOUT and IGATEPD. The
discharge time is approximately:
where VOV is the overvoltage threshold, IOUT is the load
current, and IGATEPD is the GATE’s 100mA pulldown
current.
Upon OUT falling below the threshold point, the
MAX6495/MAX6496/MAX6499s’ charge-pump current
must recover and begins recharging the external GATE
voltage. The time needed to recharge GATE from -VDto
the MOSFET’s gate threshold voltage is:
where CISS is the MOSFET’s input capacitance,
VGS(TH) is the MOSFET’s gate threshold voltage, VD is
the internal clamp (from OUTFB to GATE) diode’s for-
ward voltage (1.5V, typ) and IGATE is the charge-pump
current (100µA 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 new rise time needed to
reach a new overvoltage event can be calculated using
the following formula:
where QGD is the gate-to-drain charge.
The total period of the overvoltage waveform can be
summed up as follows:
∆tOV = ∆t1+ ∆t2+ ∆t3
The MAX6495/MAX6496/MAX6499 dissipate the most
power during an overvoltage event when IOUT = 0. The
maximum power dissipation can be approximated
using the following equation:
The die-temperature increase is related to θJC (8.3°C/W
and 8.5°C/W for the MAX6495/MAX6496/MAX6499,
respectively) of the package when mounted correctly
with a strong thermal contact to the circuit board. The
MAX6495/MAX6496/MAX6499 thermal shutdown is
governed by the equation:
TJ= TA+ PDISS (θJC +θCA) < +170°C
Based on these calculations, the parameters of the
MOSFET, the overvoltage threshold, the output load
current, and the output capacitors are external vari-
ables affecting the junction temperature. If these para-
meters are fixed, the junction temperature can also be
affected by increasing ∆t3, which is the time the switch
is on. By increasing the capacitance at the GATE pin,
∆t3increases as it increases the amount of time
required to charge up this additional capacitance
(75µA gate current). As a result, ∆tOV increases, there-
by reducing the power dissipated (PDISS).
PV I t
t
DISS OV GATEPD OV
. =× × ×0 975 1
∆
∆
∆∆
tQ
V
V
I
GD
GS
OUT
GATE
3 ≅
∆∆
VI t
C
OUT OUT
22
=
∆tC
VV
I
ISS
GS TH D
GATE
2
()
=+
∆tC V
II
OUT OV
OUT GATEPD
1
005
.
( )
=×
+
MAX6495–MAX6499
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
11
∆t2
∆t1
GATE
OUTFB
∆tOV
∆t3
Figure 5. MAX6495/MAX6496/MAX6499 Timing
MAX6495–MAX6499
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
12
OVSET
GND
GATE
IN
SHDN
OUTFB
12V IN
MAX6495
DC-DC
CONVERTER
GND
IN OUT
Figure 6. Overvoltage Limiter (MAX6495)
OVSET
GND
GATE
IN
SHDN
GATEP
OUTFB
12V
MAX6496
DC-DC
CONVERTER
GND
IN OUT
Figure 7. Overvoltage Limiter with Low-Voltage-Drop Reverse-
Protection Circuit (MAX6496)
Typical Application Circuits
OVSET
GNDPOK
GATE OUTFB
POKSET
SHDN
IN
12V
MAX6497
MAX6498
DC-DC
CONVERTER
GNDEN
IN OUT
Figure 8. Overvoltage Protection to a DC-DC Converter
(MAX6497/MAX6498)
OVSET
GND
CLEAR
GATE OUTFB
IN
SHDN
UVSET
R2
12V
R3
R1
MAX6499
DC-DC
CONVERTER
GND
IN OUT
Figure 9. Overvoltage and Undervoltage Window Detector
(MAX6499)
MAX6495–MAX6499
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
13
MAX6495
5V
IN
UVLO
1.24V
OVSET
GATE
OUTFB
GND
SHDN
10V
CHARGE
PUMP
THERMAL
PROTECTION
Figure 10. Functional Diagram (MAX6495)
Functional Diagrams
MAX6496
5V
IN
UVLO
1.24V
OVSET
GATEP
IGATEP_SOURCE
GATE
OUTFB
GND
SHDN
10V
CHARGE
PUMP
THERMAL
PROTECTION
10V
Figure 11. Functional Diagram (MAX6496)
MAX6497
MAX6498
5V
IN
UVLO
0.505V
1.24V
OVSET
GATE
OUTFB
GND
SHDN
10V
CHARGE
PUMP
THERMAL
PROTECTION
POK
POKSET
Figure 12. Functional Diagram (MAX6497/MAX6498)
MAX6499
5V
IN
UVLO
1.24V
OVSET
1.24V
UVSET
GATE
OUTFB
GND
CLEAR
SHDN
10V
CHARGE
PUMP
THERMAL
PROTECTION
Figure 13. Functional Diagram (MAX6499)
MAX6495–MAX6499
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
14
Selector Guide
PART FUNCTION p-CHANNEL
DRIVER
POK
FUNCTION UNDERVOLTAGE LATCH/
AUTORETRY PACKAGE CODE
MAX6495 OV Switch/Limiter — — — — T633-2
MAX6496 OV Switch/Limiter Yes — — — T833-2
MAX6497 OV Switch — Yes — Latch T833-2
MAX6498 OV Switch — Yes — Autoretry T833-2
MAX6499 OV/UV Switch/Limiter — — Yes Latch T833-2
134
865
N.C. GATE GND
MAX6496
2
7
OUTFB
IN OVSET GATEPSHDN
3mm x 3mm TDFN
TOP VIEW
134
865
POKSET GATE GND
MAX6497
MAX6498
2
7
OUTFB
IN OVSET POKSHDN
3mm x 3mm TDFN
134
865
UVSET GATE GND
MAX6499
2
7
OUTFB
IN OVSET CLEARSHDN
3mm x 3mm TDFN
Pin Configurations (continued)
MAX6495–MAX6499
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
15
Chip Information
PROCESS: BiCMOS
Ordering Information (continued)
Note: All devices are specified over the -40°C to +125°C operating
temperature range.
+
Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
*
EP = Exposed pad.
/
V denotes an automotive qualified part.
PART PIN-PACKAGE TOP MARK
MAX6496ATA+T 8 TDFN-EP* AOF
MAX6496ATA/V+T 8 TDFN-EP* AOF
MAX6497ATA+T 8 TDFN-EP* AOC
MAX6498ATA+T 8 TDFN-EP* AOD
MAX6499ATA+T 8 TDFN-EP* AOE
MAX6499ATA/V+T 8 TDFN-EP* AOE
Package Information
For the latest package outline information and land patterns
(footprints), go to www.maxim-ic.com/packages. Note that a
"+", "#", or "-" in the package code indicates RoHS status only.
Package drawings may show a different suffix character, but
the drawing pertains to the package regardless of RoHS status.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
6 TDFN-EP T633+2 21-0137 90-0058
8 TDFN-EP T833+2 21-0137 90-0059
MAX6495–MAX6499
72V, Overvoltage-Protection Switches/
Limiter Controllers with an External MOSFET
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. 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.
16
_______________Maxim Integrated Products, Inc. 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000
© 2012 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 7/05 Initial release. —
1 12/05 Corrected text and formula in the Detailed Description. 10, 11
2 1/07 Updated text in the Applications Information.9
3 12/08 Updated package codes in the Selector Guide. 1, 13
4 1/09 Added automotive qualified part for MAX6495. 1, 14
5 3/09 Updated Electrical Characteristics, added Peak Power Dissipation Limit section
and new Figure 4. Renumbered subsequent figures throughout data sheet. 3, 9, 10–15
6 7/09 Corrected the MAX6495ATT/V+T top mark in the Ordering Information table from
AJM to AUG. 2
7 8/09 Updated Undervoltage Monitoring (MAX6499) and Setting Overvoltage
Thresholds sections. 8, 9
8 1/11 Added soldering temperature in the Absolute Maximum Ratings section and
corrected equation. 2, 11
9 2/12 Added automotive package for MAX6499. 15
10 6/12 Added automotive package for MAX6496. 15