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MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
General Description
The MAX16126/MAX16127 load-dump/reverse-voltage
protection circuits protect power supplies from damaging
input voltage conditions, including overvoltage, reversevoltage, and high-voltage transient pulses. Using a
built-in charge pump, the devices control two external
back-to-back n-channel MOSFETs that turn off and
isolate downstream power supplies during damaging
input conditions, such as an automotive load-dump pulse
or a reverse-battery condition. Operation is guaranteed
down to 3V to ensure proper operation during automotive
cold-crank conditions. These devices feature a flag output
(FLAG) that asserts during fault conditions.
For reverse-voltage protection, external back-to-back
MOSFETs outperform the traditional reverse-battery
diode, minimizing the voltage drop and power dissipation
during normal operation.
The MAX16126/MAX16127 use external resistors to
adjust the overvoltage and undervoltage comparator
thresholds for maximum flexibility.
The MAX16127 provides limiter-mode fault management
for overvoltage and thermal shutdown conditions; whereas
the MAX16126 provides switch-mode fault management
for overvoltage and thermal shutdown conditions. In the
limiter mode, the output voltage is limited and FLAG is
asserted low during a fault. In the switch mode, the external
MOSFETs are switched off and FLAG is asserted low
after a fault. The switch mode is available in four options:
latch mode, 1 autoretry mode, 3 autoretry mode, and
always autoretry mode.
The MAX16126/MAX16127 are available in 12-pin TQFN
packages. These devices operate over the automotive
temperature range (-40°C to +125°C).
19-6053; Rev 10; 12/18
Benefits and Features
●● Increases Protection of Sensitive Electronic
Components in Harsh Environments
• -36V to +90V Wide Input-Voltage Protection Range
• Fast Gate Shutoff During Fault Conditions with
Complete Load Isolation
• Thermal-Shutdown Protection
• Active-Low FLAG Output Identifies Fault Condition
●● AEC-Q100 Automotive Qualified
• Operates Down to +3V, Riding Out Cold-Crank
Conditions
• -40°C to +125°C Operating Temperature Range
●● Integration Reduces Solution Size
• Internal Charge-Pump Circuit Enhances External
n-Channel MOSFET
• Adjustable Undervoltage/Overvoltage Thresholds
• 3mm x 3mm, 12-Pin TQFN Package
●● Reduced Power Dissipation Compared to Discrete
Solutions
• Minimal Operating Voltage Drop for ReverseVoltage Protection
• 350μA (max) Supply Current and 100μA (max)
Shutdown Current at 30V Input
Applications
●● Automotive
●● Industrial
●● Avionics
●● Telecom/Server/Networking
Ordering Information appears at end of data sheet.
MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
Absolute Maximum Ratings
Continuous Sink/Source (all pins)...................................±100mA
Continuous Power Dissipation (TA = +70°C) (multilayer board)
TQFN (derate 14.7mW/°C above +70°C)............... 1176.5mW
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
(All pins referenced to GND.)
IN .............................................................................-36V to +90V
SHDN............................................-0.3V to max (0V, VIN + 0.3V)
TERM............................................-0.3V to max (0V, VIN + 0.3V)
SRC, GATE.............................................................-36V to +45V
SRC to GATE..........................................................-36V to +36V
OUT........................................................................-0.3V to +45V
FLAG......................................................................-0.3V to +45V
OVSET, UVSET........................................................-0.3V to +6V
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.
Package Thermal Characteristics (Note 1)
TQFN
Junction-to-Ambient Thermal Resistance (θJA)...........68°C/W
Junction-to-Case Thermal Resistance (θJC)................11°C/W
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer
board. For detailed information on package thermal considerations, refer to www.maximintegrated.com/thermal-tutorial.
Electrical Characteristics
(VIN = 12V, CGATE-SOURCE = 1nF, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2)
PARAMETER
Input Voltage Range
SYMBOL
VIN
CONDITIONS
30
Protection range
-36
+90
IIN
IN Undervoltage Lockout
OVSET/UVSET Input Current
OVSET/UVSET Threshold (Rising)
ISRC
VUVLO
VIN = VSRC =
VOUT = 12V
224
360
VIN = VSRC =
VOUT = 30V
260
400
VIN = 12V
34
60
VIN = 30V
64
100
VSRC = VIN = 12V, SHDN = high
136
200
VSRC = VIN = 30V, SHDN = high
240
350
VIN rising
IUVSET/OVSET
VTH
MAX
3
SHDN = low
SRC Input Current
TYP
Operating range
SHDN = high
Input Supply Current
MIN
VIN rising
1.2
1.225
UNITS
V
µA
µA
2.92
V
100
nA
1.25
V
VTH-HYS
0.05 x
VTH
V
POK Threshold Rising
VPOK+
0.9 x
VIN
V
POK Threshold Falling
VPOK-
0.87 x
VIN
V
TERM On-Resistance
RTERM
0.7
OVSET/UVSET Threshold Hysteresis
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1.2
kΩ
Maxim Integrated │ 2
MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
Electrical Characteristics (continued)
(VIN = 12V, CGATE-SOURCE = 1nF, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2)
PARAMETER
SYMBOL
Startup Response Time
tSTART
CONDITIONS
MIN
(Note 3)
TYP
150
Autoretry Timeout
tRETRY
GATE Rise Time
tRISE
VGATE rising (GND to VSRC + 8V)
OVSET-to-GATE Propagation Delay
tOVG
VOVSET rising (VTH - 100mV to
VTH + 100mV)
UVSET-to-GATE Propagation Delay
tUVG
VUVSET falling (VTH + 100mV to
VTH - 100mV)
20
Output Input Resistance to GND
ROUT
MAX16126
4
MAX16127
2
OVSET-to-FLAG Propagation Delay
GATE Output Voltage High Above
VSRC
GATE Pulldown Current
GATE Charge-Pump Current
Thermal Shutdown
tOV
VGS
IPD
IGATE
δT
SHDN Logic-High Input Voltage
VIH
SHDN Logic-Low Input Voltage
VIL
SHDN Input Pulse Width
tPW
SHDN Input Pulldown Current
ISPD
FLAG Output Voltage Low
VOL
FLAG Leakage Current
VOVSET rising (VTH - 100mV to
VTH + 100mV)
IIL
150
ms
1
ms
µs
µs
MΩ
0.3
µs
VIN = VSRC = VOUT = 3V,
IGATE = -1FA
4.25
5
5.5
VIN = VSRC = VOUT = 12V,
IGATE = -1FA
8
9
10
VIN = VSRC = VOUT = 24V,
IGATE = -1FA
7
8.5
10
VIN = VSRC = VOUT = 30V,
IGATE = -1FA
6.25
8
9.5
VGATE = 12V
8.8
VIN = VGATE = VSRC = 12V
UNITS
µs
0.55
T+
Thermal-Shutdown Hysteresis
MAX
V
mA
180
µA
+145
°C
15
°C
1.4
V
0.4
6
V
µs
0.8
1.2
µA
FLAG sinking 1mA
0.4
V
VFLAG = 12V
0.5
µA
Note 2: All parameters are production tested at TA = +25°C. Limits over the operating temperature range are guaranteed by design.
Note 3: The MAX16126/MAX16127 power up with the external MOSFETs in off mode (VGATE = VSRC). The external MOSFETs turn
on tSTART after the IC is powered up and all input conditions are valid.
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Maxim Integrated │ 3
MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
Typical Operating Characteristics
(VIN = 12V, TA = +25°C, unless otherwise noted.)
150
100
270
100
250
230
210
190
20
30
80
30
25
20
1.0
0.9
40
0.8
6
12
18
24
GATE-TO-SOURCE VOLTAGE
vs. SUPPLY VOLTAGE
0.7
0.6
0.5
0.4
0.3
0.2
10
9
8
7
6
5
4
3
2
1
0
0
-40 -25 -10 5 20 35 50 65 80 95 110 125
5
10
15
20
25
30
TEMPERATURE (°C)
VIN (V)
GATE-TO-SOURCE VOLTAGE
vs. TEMPERATURE
GATE PULLDOWN CURRENT
vs. TEMPERATURE
GATE-PULLUP CURRENT
vs. SUPPLY VOLTAGE
8.8
8.4
8.0
7.6
7.2
VIN = VSRC = VOUT = 12V
GATE ENHANCED
6.0
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C )
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14
11
8
200
35
MAX16126 toc09
17
VGATE = 12V
VSRC = GND
180
GATE PULL-UP CURRENT(µA)
9.2
20
GATE PULLDOWN CURRENT (mA)
MAX16126 toc07
9.6
MAX16126 toc08
TEMPERATURE (°C)
10.0
30
SUPPLY VOLTAGE (V)
0
-40 -25 -10 5 20 35 50 65 80 95 110 125
50
0
0.1
10
60
10
100 120
MAX16126 toc05
MAX16126 toc04
SHDN = LOW
SHDN PULLDOWN CURRENT (µA)
SUPPLY CURRENT (µA)
60
SHDN PULLDOWN CURRENT
vs. TEMPERATURE
15
GATE-TO-SOURCE VOLTAGE (V)
40
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
35
6.4
20
TEMPERATURE (°C)
40
6.8
0
SUPPLY VOLTAGE (V)
50
45
-40 -20
40
GATE-TO-SOURCE VOLTAGE (V)
10
70
20
150
0
80
30
170
50
SHDN = LOW
90
MAX16126 toc06
200
SHDN = HIGH
GATE ENHANCED
SUPPLY CURRENT (µA)
SUPPLY CURRENT (µA)
250
290
MAX16126 toc02
SHDN = HIGH
GATE ENHANCED
SUPPLY CURRENT (µA)
310
MAX16126 toc01
300
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
SUPPLY CURRENT vs. TEMPERATURE
MAX16126 toc03
SUPPLY CURRENT vs. SUPPLY VOLTAGE
160
140
120
100
80
60
40
VIN = VGATE = VSRC
GATE ENHANCED
20
0
5
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
0
5
10
15
20
25
30
VIN (V)
Maxim Integrated │ 4
MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
Typical Operating Characteristics (continued)
(VIN = 12V, TA = +25°C, unless otherwise noted.)
1.1
FALLING
0.9
MAX16126 toc10b
RISING
1.3
0.7
0.5
0.4
FLAG VOLTAGE (V)
OVSET THRESHOLD (V)
1.3
1.5
UVSET THRESHOLD (V)
RISING
MAX16126 toc10a
1.5
FLAG OUTPUT LOW VOLTAGE
vs. CURRENT
UVSET THRESHOLD vs. TEMPERATURE
1.1
FALLING
0.9
0.7
0.5
0.3
0.2
0.1
0.5
-40 -25 -10 5 20 35 50 65 80 95 110 125
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
TEMPERATURE (°C)
0
0
0.50
0.25
1.5
2.0
MAX16126 toc13
30
25
REVERSE CURRENT (µA)
0.75
1.0
REVERSE CURRENT
vs. REVERSE VOLTAGE
MAX16126 toc12
PROPAGATION DELAY (µs)
VOVSET PULSED FROM
(VTH - 100mV) TO (VTH + 100mV)
0.5
FLAG CURRENT (mA)
OVERVOLTAGE FAULT TO GATE
PROPAGATION DELAY vs. TEMPERATURE
1.00
MAX16126 toc11
OVSET THRESHOLD vs. TEMPERATURE
20
15
10
5
0
0
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
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0
5
10
15
20
25
30
REVERSE VOLTAGE (V)
Maxim Integrated │ 5
MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
Typical Operating Characteristics (continued)
(VIN = 12V, TA = +25°C, unless otherwise noted.)
STARTUP WAVEFORM
(VIN = 0 TO 12V, RL = 100I,
CIN = 0.1µF, COUT = 100µF)
STARTUP FROM SHUTDOWN
(SHDN RISING 0 TO 2V, VIN = 12V,
RLOAD = 100I, CIN = 0.1µF)
MAX16126 toc14
MAX16126 toc15
VIN
10V/div
VSHDN
2V/div
VGATE
10V/div
VGATE
10V/div
VOUT
10V/div
VOUT
10V/div
400µs/div
400µs/div
OVERVOLTAGE SWITCH FAULT
(VOV = 20V, CIN = 0.1µF, COUT = 100µF)
OVERVOLTAGE LIMITER
(VUV = 4V, VOV = 20V,
CIN = 0.1µF, COUT = 100µF)
MAX16126 toc16
VIN
20V/div
MAX16126 toc17
VIN
20V/div
VGATE
20V/div
VOUT
10V/div
VGATE
10V/div
VOUT
20V/div
100ms/div
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20ms/div
Maxim Integrated │ 6
MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
FLAG
I.C.
TOP VIEW
OUT
Pin Configuration
9
8
7
SRC 10
MAX16126
MAX16127
GATE 11
EP
SHDN
1
2
3
N.C.
+
TERM
IN 12
6
GND
5
OVSET
4
UVSET
TQFN
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Maxim Integrated │ 7
MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
Pin Description
PIN
NAME
FUNCTION
1
SHDN
Shutdown Input. Drive SHDN low to force GATE and FLAG low and turn off the external n-channel
MOSFETs. Connect a 100kΩ resistor from SHDN to IN for normal operation.
2
TERM
Voltage-Divider Termination Output. TERM is internally connected to IN. TERM is high impedance when
SHDN is low, forcing the current to zero in the resistive-divider connected to TERM.
3
N.C.
4
UVSET
Undervoltage Threshold Adjustment Input. Connect UVSET to the external resistive voltage-divider
network to adjust the desired input undervoltage threshold. Connect the resistive divider to TERM.
5
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 resistive divider to
TERM for overvoltage switch-mode applications or to OUT for overvoltage limiting applications.
6
GND
7
I.C.
8
FLAG
FLAG Output. During startup, FLAG is low as long as VOUT is lower than 90% of VIN and after that
it is high impedance. It asserts low during shutdown mode, an overvoltage, thermal shutdown, or
undervoltage fault or when VOUT falls below 90% of VIN.
9
OUT
Output Voltage-Sense Input. Connect OUT to the load with a 100Ω series resistor. Bypass the load with a
minimum 10µF capacitor to GND.
10
SRC
Source Input. Connect SRC to the common source connection of the external MOSFETs. When the
MOSFETs are turned off, this connection is clamped to GND. An external zener diode between SRC and
GATE protects the gates of the external MOSFETs.
11
GATE
Gate-Driver Output. Connect GATE to the gates of the external n-channel MOSFETs. GATE is the
charge-pump output during normal operation. GATE is quickly pulled low during a fault condition or when
SHDN is pulled low.
12
IN
Positive Supply Input Voltage. Connect IN to the positive side of the input voltage. Bypass IN with a
0.1µF ceramic capacitor to GND.
—
EP
Exposed Pad. Can be connected to GND or left unconnected.
No Connection. Not internally connected.
Ground
Internally Connected. Connect to GND.
Detailed Description
The MAX16126/MAX16127 transient protection circuits are
suitable for automotive and industrial applications where
high-voltage transients are commonly present on supply
voltage inputs. The devices monitor the input voltage and
control two external common-source n-channel MOSFETs
to protect downstream voltage regulators during load-dump
events or other automotive pulse conditions.
dissipation and voltage drop, and allows the circuit to
operate at very low cold-crank voltages (3V minimum).
The devices feature an overvoltage and an undervoltage
comparator for voltage window detection. A flag output
(FLAG) asserts when a fault event occurs.
The MAX16127 provides a limiter-mode fault management for overvoltage and thermal shutdown conditions,
whereas the MAX16126 provides switch-mode fault
management for overvoltage and thermal shutdown conditions. In the limiter mode, the MOSFETs cycle on and
off so the output voltage is limited. In the switch mode,
the external MOSFETs are switched off, disconnecting
the load from the input. In both cases, FLAG asserts to
indicate a fault.
Two external back-to-back n-channel MOSFETs provide
reverse-voltage protection and also prevent reverse current during a fault condition. Compared to a traditional
reverse-battery diode, this approach minimizes power
The MAX16126/MAX16127 use a charge pump to generate the GATE to SRC voltage and enhance the external
MOSFETs. After the input voltage exceeds the input
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Gate Charge Pump
Maxim Integrated │ 8
MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
undervoltage threshold, the charge pump turns on after
a 150Fs delay.
During a fault condition, GATE is pulled to ground with a
8.8mA (min) pulldown current. Note that an external zener
diode is required to be connected between the gate and
source of the external MOSFETs. See the Applications
Information section.
Overvoltage Protection
The MAX16126/MAX16127 detect overvoltage conditions
using a comparator that is connected through an external
resistive divider to the input or output voltage. An overvoltage condition causes the GATE output to go low, turning
off the external MOSFETs. FLAG also asserts to indicate
the fault condition.
Overvoltage Limiter (MAX16127)
In overvoltage limiter mode, the output voltage is regulated at the overvoltage threshold voltage and continues
to supply power to downstream devices. In this mode, the
device operates like a voltage regulator.
During normal operation, GATE is enhanced 9V above
SRC. The output voltage is monitored through a resistive divider between OUT and OVSET. When OUT rises
above the overvoltage threshold, GATE goes low and the
MOSFETs turn off. As the voltage on OUT falls below the
overvoltage threshold minus the threshold hysteresis,
GATE goes high and the MOSFETs turn back on again,
regulating OUT in a switched-linear mode at the overvoltage threshold.
The switching frequency depends on the gate charge of
the MOSFETs, the charge-pump current, the output load
current, and the output capacitance.
Caution must be exercised when operating the
MAX16127 in voltage-limiting mode for long durations.
Since MOSFETs can dissipate power continuously during
this interval, proper heat sinking should be implemented
to prevent damage to them.
Overvoltage Switch (MAX16126)
In the overvoltage switch mode, the internal overvoltage comparator monitors the input voltage and the load
is completely disconnected from the input during an
overvoltage event. When the input voltage exceeds the
overvoltage threshold, GATE goes low and the MOSFETs
turn off, disconnecting the input from the load. After that,
for the autoretry mode version, the autoretry timer starts,
while for the latched mode version a power cycle to IN or
a cycle on SHDN is needed to turn the external MOSFETs
back on.
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The MAX16126 can be configured to latch off (suffix D)
even after the overvoltage condition ends. The latch is
cleared by cycling IN below the undervoltage threshold or
by toggling SHDN.
The devices can also be configured to retry:
U One time, then latch off (suffix B)
U Three times, then latch off (suffix C)
U Always retry and never latch off (suffix A)
There is a fixed 150ms (typ) delay between each retry
attempt. If the overvoltage fault condition is gone when a
retry is attempted, GATE goes high and power is restored
to the downstream circuitry.
Undervoltage Protection
The MAX16126/MAX16127 monitor the input voltage
for undervoltage conditions. If the input voltage is below
the undervoltage threshold (VIN < VTH - VTH-HYS),
GATE goes low, turning off the external MOSFETs and
FLAG asserts. When the input voltage exceeds the
undervoltage threshold (VIN > VTH), GATE goes high
after a 150Fs delay (typ).
For the MAX16126/MAX16127, an external resistive
divider connected between TERM, UVSET, and GND
sets the undervoltage threshold (TERM is connected to
IN when SHDN is high).
Thermal Shutdown
The MAX16126/MAX16127 thermal shutdown feature
turns off the MOSFETs if the internal die temperature exceeds +145°C (TJ). By ensuring good thermal
coupling between the MOSFETs and the MAX16126/
MAX16127, the thermal shutdown can turn off the
MOSFETs if they overheat.
When the junction temperature exceeds TJ = +145°C
(typ), the internal thermal sensor signals the shutdown
logic, pulling the GATE voltage low and allowing the
device to cool. When TJ drops by 15°C (typ), GATE goes
high and the MOSFETs turn back on. Do not exceed
the absolute maximum junction-temperature rating of
TJ = +150°C.
Flag Output (FLAG)
An open-drain FLAG output indicates fault conditions.
During startup, FLAG is initially low and goes high
impedance when VOUT is greater than 90% of VIN if no
fault conditions are present. FLAG asserts low during
shutdown mode, an overvoltage, thermal shutdown, or
undervoltage fault, or when VOUT falls below 90% of VIN.
Maxim Integrated │ 9
MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
TERM Connection
Reverse-Voltage Protection
The MAX16126/MAX16127 integrate reverse-voltage
protection, preventing damage to the downstream circuitry caused by battery reversal or negative transients.
The devices can withstand reverse voltage to -36V
without damage to themselves or the load. During a
reverse-voltage condition, the two external n-channel
MOSFETs are turned off, protecting the load. Connect
a 0.1µF ceramic capacitor from IN to GND, connect a
10nF ceramic capacitor from GATE to SRC, connect
10µF from the load to GND, and minimize the parasitic
capacitance from GATE to GND to have a fast reservebattery voltage-transient protection. During normal
operation, both MOSFETs are turned on and have a minimal forward voltage drop, providing lower power dissipation and a much lower voltage drop than a reverse-battery
protection diode.
Supply Current During Fault Conditions
During fault conditions, the MAX16126/MAX16127
supply current is higher than normal operation. When a
fault condition occurs, the MAX16126/MAX16127 pulls the
gate low but keeps the charge pump active. This results
in increased supply because the charge pump tries hard
to bring up the gate. See Figures below for supply current
during overvoltage and undervotlage fault conditions.
OV FAULT MODE SUPPLY CURRENT VS.
SUPPLY VOLTAGE
2.0
1.8
SUPPLY CURRENT(mA)
1.6
TA = +125°C
1.4
TA = +25°C
1.2
1.0
TA = -40°C
0.8
0.6
0.4
0.2
0
0
10
20
30
UV FAULT SUPPLY CURRENT VS.
SUPPLY VOLTAGE
2.0
1.8
1.6
SUPPLY CURRENT(mA)
The TERM connection has an internal switch to IN.
In shutdown (SHDN = GND), this switch is open. By
connecting the voltage threshold resistive divider to
TERM instead of directly to IN, power dissipation in the
resistive divider can be eliminated and the shutdown
supply current reduced.
1.4
TA = +125°C
1.2
TA = +25°C
TA = -40°C
1.0
0.8
0.6
0.4
0.2
0
0
10
20
30
SUPPLY VOLTAGE (V)
Applications Information
Automotive Electrical Transients
(Load Dump)
Automotive circuits generally require supply voltage
protection from various transient conditions that occur in
automotive systems. Several standards define various
pulses that can occur. Table 1 summarizes the pulses
from the ISO 7637-2 specification.
Most of the pulses can be mitigated with capacitors and zener clamp diodes (see the Typical
Operating Characteristics and also the Increasing the
Input Voltage Protection Range section). The load dump
(pulse 5a and 5b) occurs when the alternator is charging
the battery and a battery terminal gets disconnected. Due
to the sudden change in load, the alternator goes out of
regulation and the bus voltage spikes. The pulse has a
rise time of about 10ms and a fall time of about 400ms,
but can extend out to 1s or more depending on the characteristics of the charging system. The magnitude of the
pulse depends on the bus voltage and whether the system
is unsuppressed or uses central load-dump suppression
(generally implemented using very large clamp diodes
built into the alternator). Table 1 lists the worst-case
values from the ISO 7637-2 specification.
Cold crank (pulse 4) occurs when activating the starter
motor in cold weather with a marginal battery. Due to the
large load imposed by the starter motor, the bus voltage
sags. Since the MAX16126/MAX16127 can operate down
to 3V, the downstream circuitry can continue to operate
through a cold-crank condition. If desired, the undervoltage threshold can be increased so that the MOSFETs turn
SUPPLY VOLTAGE (V)
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Maxim Integrated │ 10
MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
Table 1. Summary of ISO 7637 Pulses
NAME
DESCRIPTION
Pulse 1
Inductive load disconnection
Pulse 2a
Inductive wiring disconnection
Pulse 3a
PEAK VOLTAGE (V) (max)*
12V SYSTEM
-100
1ms to 2ms
50
0.05ms
-150
Switching transients
Pulse 3b
DURATION
0.2µs
100
-7
100ms (initial)
-6
Up to 20s
Pulse 4
Cold crank
Pulse 5a
Load dump (unsuppressed)
87
Pulse 5b
Load dump (suppressed)
(Varies, but less than pulse 5a)
400ms (single)
*Relative to system voltage.
off during a cold crank, disconnecting the downstream
circuitry. An output reservoir capacitor can be connected
from OUT to GND to provide energy to the circuit during
the cold-crank condition.
Refer to the ISO 7637-2 specification for details on pulse
waveforms, test conditions, and test fixtures.
Setting Overvoltage and Undervoltage
Thresholds (MAX16126)
The MAX16126 uses an external resistive divider to set the
overvoltage and undervoltage thresholds. The MAX16126
operates in switch mode in which the internal overvoltage
comparator monitors the input voltage. It uses three resistors in a single resistive divider to set the undervoltage
and overvoltage thresholds. The top of the resistive divider
connects to TERM (see Figure 1).
The MAX16126 includes internal undervoltage and overvoltage comparators for window detection. GATE is
enhanced and the n-channel MOSFETs are on when
the IN 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, the
GATE voltage goes to GND, turning off the MOSFETs.
The circuit in Figure 1 shows the MAX16126 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:
R
VTRIPLOW = (VTH - VTH-HYS ) TOTAL
R2 + R3
R
VTRIPHIGH = VTH TOTAL
R3
where RTOTAL = R1 + R2 + R3, VTH is the 1.225V
OVSET/UVSET threshold, and VTH-HYS is the hysteresis.
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.
2) Calculate R3 based on RTOTAL and the desired upper
trip point:
V × R TOTAL
R3 = TH
VTRIPHIGH
3) Calculate R2 based on RTOTAL, R3, and the desired
lower trip point:
R2 =
(VTH - VTH-HYS ) × R TOTAL
- R3
VTRIPLOW
4) Calculate R1 based on RTOTAL, R2, and R3:
R1 = R TOTAL - R2 - R3
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Maxim Integrated │ 11
MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
VIN
10nF
GATE
100I
SRC
10µF
DC-DC
CONVERTER
IN
OUT
GND
OUT
IN
100kI
SHDN
0.1µF
TERM
MAX16126
FLAG
R1
UVSET
R2
OVSET
R3
GND
Figure 1. Overvoltage and Undervoltage Window Detector Circuit (MAX16126)
Setting Overvoltage and Undervoltage
Thresholds (MAX16127)
The MAX16127 operates in limiter mode and uses
separate resistive dividers to set the undervoltage and
overvoltage thresholds. The top of the overvoltage divider
connects to OUT and the top of the undervoltage divider
connects to TERM (see Figure 2).
Use the following formula to calculate R4:
=
R4 VTH ×
R TOTAL_OV
VOV
where RTOTAL_OV = R3 + R4, VTH is the 1.225V OVSET
rising threshold, and VOV is the desired overvoltage
threshold. The falling threshold of VTH is 5% below the
rising threshold.
Similarly, to calculate the values of R1 and R2:
R
=
R2 (VTH - VTH-HYS ) × TOTAL_UV
VUV
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where RTOTAL_UV = R1 + R2, VTH is the 1.225V UVSET
rising threshold, VTH-HYS is the hysteresis, and VUV is
the desired undervoltage threshold.
Use the nearest standard-value resistor that is less
than the calculated value. A lower value for total resistance dissipates more power, but provides slightly better
accuracy.
MOSFET Selection
MOSFET selection is critical to design a proper protection circuit. Several factors must be taken into account:
the gate capacitance, the drain-to-source voltage rating,
the on-resistance (RDS(ON)), the peak power dissipation
capability, and the average power dissipation limit. In general, both MOSFETs should have the same part number.
For size-constrained applications, a dual MOSFET can
save board area. Select the drain-to-source voltage so
that the MOSFETs can handle the highest voltage that
might be applied to the circuit. Gate capacitance is not as
critical, but it does determine the maximum turn-on and
turn-off time. MOSFETs with more gate capacitance tend
to respond more slowly.
Maxim Integrated │ 12
MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
DC-DC
CONVERTER
VIN
IN
10µF
10nF
OUT
GND
100I
100kI
IN
GATE
SRC
OUT
SHDN
0.1µF
MAX16127
FLAG
TERM
R3
R1
OVSET
UVSET
R2
GND
R4
Figure 2. Overvoltage and Undervoltage Limiter Protection Configuration (MAX16127)
MOSFET Power Dissipation
The RDS(ON) must be low enough to limit the MOSFET
power dissipation during normal operation. Power
dissipation (per MOSFET) during normal operation can be
calculated using this formula:
P = ILOAD2 x RDS(ON)
where P is the power dissipated in each MOSFET and
ILOAD is the average load current.
During a fault condition in switch mode, the MOSFETs
turn off and do not dissipate power. Limiter mode
imposes the worst-case power dissipation. The average
power can be computed using the following formula:
P = ILOAD x (VIN - VOUT)
where P is the average power dissipated in both
MOSFETs, ILOAD is the average load current, VIN is the
input voltage, and VOUT is the average limited voltage
on the output. In limiter mode, the output voltage is a
sawtooth wave with characteristics determined by the
RDS(ON) of the MOSFETs, the output load current, the
output capacitance, the gate charge of the MOSFETs,
and the GATE charge-pump current.
Since limiter mode can involve high switching currents
when the GATE is turning on at the start of a limiting
cycle (especially when the output capacitance is high), it
is important to ensure the circuit does not violate the peak
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power rating of the MOSFETs. Check the pulse power ratings in the MOSFET data sheet.
MOSFET Gate Protection
To protect the gate of the MOSFETs, connect a zener
clamp diode from the gate to the source. The cathode
connects to the gate, and the anode connects to the
source. Choose the zener clamp voltage to be above 10V
and below the MOSFET VGS maximum rating.
Increasing the
Input Voltage Protection Range
The MAX16126/MAX16127 can tolerate -36V to +90V.
To increase the positive input voltage range protection,
connect two back-to-back zener diodes from IN to system
ground, and connect a resistor in series with IN and the
power-supply input to limit the current drawn by the zener
diodes (see Figure 3).
Zener diode D1 clamps positive voltage excursions and
D2 clamps negative voltage excursions. Set the zener
voltages so the worst-case voltages do not exceed the
ratings of the part. Also ensure that the zener diode power
ratings are not exceeded. The combination of the series
resistor and the zener diodes also help snub pulses on
the supply voltage input and can aid in clamping the lowenergy ISO 7637-2 pulses.
Maxim Integrated │ 13
MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
It is important to compute the peak power dissipation
in the series resistor. Most standard surface-mount
resistors cannot withstand the peak power dissipation
during certain pulse events. Check the resistor data
sheets for pulse power derating curves. If necessary, connect multiple resistors in parallel or use automotive-rated
resistors.
The circuit in Figure 4 shows the recommended arrangement. When VIN = 35V, VGATE = 35V + 6.8V or 41.8V.
When VIN > 35V, the MAX16126/MAX16127 detects
the input over voltage condition by sensing the voltage
at the OVSET pin and turns off the charge pump. The
resistive voltage divider on OVSET must be selected to
disable the circuit before the gate voltage reaches 45V.
The MAX16126TCA/MAX16127TCA automatically reenable GATE drive when the input voltage drops 5% below
the overvoltage threshold. For the MAX16126TCD, the
latch-mode option, GATE drive is enabled by either power
cycling the IN voltage below UVLO threshold or by toggling SHDN. See the Ordering Information section for
other available options.
The shutdown input needs a series resistor to limit the
current if VIN exceeds the clamped voltage on IN. A good
starting point is 100kI
Increasing the
Input Voltage Operating Range
With proper external component selection, the MAX16126/
MAX16127’s input voltage operating range can be extended beyond 30V. Normally the input voltage can swing up
to 90V in protection mode, but normal operation is listed in
the electrical characteristics table to 30V. Higher voltage
operation is permissible so long as the resulting GATE
bias voltage does not exceed 45V with respect to GND.
Output Reservoir Capacitor
The output capacitor can be used as a reservoir capacitor to allow downstream circuitry to ride out fault transient
conditions. Since the voltage at the output is protected
from input voltage transients, the capacitor voltage rating
can be less than the expected maximum input voltage.
To enable operating voltages above 30V, a 6.8V
Zener diode clamp can be added GATE-to-SRC to the
external switches to limit the maximum GATE voltage.
DC-DC
CONVERTER
VBATT
IN
10nF
RS
100I
100I
10µF
*
GATE
SRC
OUT
GND
*
OUT
IN
D1
100kI
SHDN
D2
MAX16126
MAX16127
FLAG
*
GND
*SYSTEM GROUND
Figure 3. Circuit to Increase Input Voltage Protection Range
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Maxim Integrated │ 14
MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
6.8V
VIN
VOUT
100I
IN
10µF
OUT
GATE
SRC
10nF
100kI
SHDN
0.1µF
MAX16127
TERM
37.9kI
GND
OVSET
1.37kI
Figure 4. Use of a 6.8V Zener Clamp to Enable Operation with VIN Up to 35V
VOUT
VIN
10nF
100I
GATE
SRC
COUT
10µF
OUT
IN
100kI
SHDN
0.1µF
TERM
MAX16126
FLAG
R1
UVSET
R2
OVSET
R3
GND
Figure 5. MAX16126 Typical Operating Circuit
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Maxim Integrated │ 15
MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
VOUT
VIN
10nF
10µF
100I
GATE
SRC
OUT
R3
IN
100kI
SHDN
0.1µF
OVSET
MAX16127
TERM
R4
R1
UVSET
FLAG
R2
GND
Figure 6. MAX16127 Typical Operating Circuit
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Maxim Integrated │ 16
MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
GATE
SRC
CHARGE
PUMP
MAX16126
MAX16127
IN
OUT
UVLO
POWER-OK
TERM
UVSET
SHDN
1.225V
FLAG
CONTROL LOGIC
OVSET
THERMAL
PROTECTION
1.225V
GND
Figure 7. MAX16126/MAX16127 Functional Diagram
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Maxim Integrated │ 17
MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
Ordering Information
PART
PIN-PACKAGE
TOP MARK
FUNCTION
MAX16126TCA+
12 TQFN-EP
+ABV
MAX16126TCA/V+
12 TQFN-EP
+ACR
MAX16126TCA/VY+*
12 TQFN-EP
+ACR
MAX16126TCB+
12 TQFN-EP
+ABX
MAX16126TCB/V+
12 TQFN-EP
+ADT
MAX16126TCC+
12 TQFN-EP
+ABY
MAX16126TCC/V+
12 TQFN-EP
+ADU
MAX16126TCD+
12 TQFN-EP
+ABZ
MAX16126TCD/V+*
12 TQFN-EP
+ADH
MAX16127TC+
12 TQFN-EP
+ABW
Limiter mode
MAX16127TC/V+
12 TQFN-EP
+AGC
Limiter mode
Always autoretry
One retry, then latch
Switch mode
Three retries, then latch
Latch mode
Note: All devices are specified over the -40°C to +125°C temperature range.
+Denotes a lead(Pb)-free/RoHS-compliant package.
/V denotes an automotive qualified part.
*Future product—contact factory for availability.
EP = Exposed pad.
Chip Information
PROCESS: BiCMOS
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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.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
12 TQFN-EP
T1233+4
21-0136
90-0019
12 TQFN-EP
T1233Y+4
21-100171
90-100060
12 TQFN-EP
T1233+5
21-100319
90-0019
Maxim Integrated │ 18
MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
Revision History
REVISION
NUMBER
REVISION
DATE
PAGES
CHANGED
0
11/11
Initial release
1
6/12
Revised the Electrical Characteristics, Typical Operating Characteristics, the
Overvoltage Limiter (MAX16127), Reverse-Voltage Protection, and the Increasing the
Input Voltage Protection Range sections and Figure 3.
2
12/12
Updated Input Supply Current, SRC Input Current, and GATE Output Voltage High
Above VSRC conditions in the Electrical Characteristics and updated Figure 3
3
12/13
Updated Figure 3
4
1/14
Added /V automotive OPNs to Ordering Information
5
10/14
Added Increasing the Input Voltage Operating Range section and new Figure 4
6
3/15
Updated Benefits and Features section
1
7
8/17
Corrected Ordering Information table
18
8
4/18
Added Supply Current During Fault Conditions section
10
9
9/18
Updated the Pin Description table and Reverse-Voltage Protection section. Added
MAX16127TC/V+* to Ordering Information and package code T1233+5 to the
Package Information.
8, 10, 18
10
12/18
Updated Electrical Characteristics, Ordering Information, and Package Information
2, 3, 18
DESCRIPTION
—
1–3, 4, 9, 10,
14
2, 3, 14
12
18
14–17
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.
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 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.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
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