AVAILABLE
Functional Diagrams
Pin Configurations appear at end of data sheet.
Functional Diagrams continued at end of data sheet.
UCSP is a trademark of Maxim Integrated Products, Inc.
For pricing, delivery, and ordering information, please contact Maxim Direct
at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.
Load-Dump/Reverse-Voltage Protection Circuits
19-6053; Rev 0; 11/11
General Description
The MAX16126/MAX16127 load-dump/reverse-voltage
protection circuits protect power supplies from dam-
aging input voltage conditions, including overvoltage,
reverse-voltage, and high-voltage transient pulses. Using
a built-in charge pump, the devices control two exter-
nal 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 automo-
tive 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 dissipa-
tion 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 manage-
ment for overvoltage and thermal shutdown conditions;
whereas the MAX16126 provides switch-mode fault
management for overvoltage and thermal shutdown con-
ditions. 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 (-40NC to +125NC).
Applications
Automotive
Industrial
Avionics
Telecom/Server/Networking
Benefits and Features
S Operates Down to +3V, Riding Out Cold-Crank
Conditions
S -30V to +90V Wide Input Voltage Protection Range
S Minimal Operating Voltage Drop Reverse-Voltage
Protection
S Fast Gate Shutoff During Fault Conditions with
Complete Load Isolation
S Adjustable Undervoltage/Overvoltage Thresholds
S Thermal Shutdown Protection
S Low Supply Current and Low Shutdown Current
S Charge-Pump Circuit Enhances External
n-Channel MOSFETs
S FLAG Output Identifies Fault Condition
S Automotive Qualified
S -40NC to +125NC Operating Temperature Range
S Available in 3mm x 3mm, 12-Pin TQFN Package
Ordering Information appears at end of data sheet.
For related parts and recommended products to use with this part,
refer to www.maxim-ic.com/MAX16126.related.
MAX16126/MAX16127
Load-Dump/Reverse-Voltage Protection Circuits
(All pins referenced to GND.)
IN ............................................................................-30V to +90V
SHDN ............................................-0.3V to max (0V, VIN + 0.3V)
TERM ............................................-0.3V to max (0V, VIN + 0.3V)
SRC, GATE ............................................................. -30V to +45V
SRC to GATE .......................................................... -30V to +30V
OUT .......................................................................-0.3V to +45V
FLAG .....................................................................-0.3V to +45V
OVSET, UVSET ........................................................ -0.3V to +6V
Continuous Sink/Source (all pins) ................................. Q100mA
Continuous Power Dissipation (TA = +70NC) (multilayer board)
TQFN (derate 14.7mW/NC above +70NC)...............1176.5mW
Operating Temperature Range ........................ -40NC to +125NC
Junction Temperature .....................................................+150NC
Storage Temperature Range ............................ -60NC to +150NC
Lead Temperature (soldering, 10s) ................................+300NC
Soldering Temperature (reflow) ......................................+260NC
TQFN
Junction-to-Ambient Thermal Resistance (BJA) ..........68NC/W
Junction-to-Case Thermal Resistance (BJC) ...............11NC/W
ABSOLUTE MAXIMUM RATINGS
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.maxim-ic.com/thermal-tutorial.
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional opera-
tion 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)
ELECTRICAL CHARACTERISTICS
(VIN = 12V, CGATE-SOURCE = 1nF, TA = -40NC to +125NC, unless otherwise noted. Typical values are at TA = +25NC.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Input Voltage Range VIN
Operating range 3 24 V
Protection range -30 +90
Input Supply Current IIN
SHDN = high 224 320 FA
SHDN = low 34 50
SRC Input Current ISRC 75 110 FA
IN Undervoltage Lockout VUVLO VIN rising 2.8 V
OVSET/UVSET Input Current IUVSET/OVSET 500 nA
OVSET/UVSET Threshold (Rising) VTH VIN rising 1.2 1.225 1.25 V
OVSET/UVSET Threshold Hysteresis VTH-HYS 5 %
POK Threshold Rising VPOK+ 0.9 x VIN V
POK Threshold Falling VPOK- 0.87 x VIN V
TERM On-Resistance RTERM 0.7 1.2 kI
Startup Response Time tSTART (Note 3) 150 Fs
Autoretry Timeout tRETRY 150 ms
GATE Rise Time tRISE VGATE rising (GND to VSRC + 6V) 1 ms
OVSET to GATE Propagation Delay tOVG VOVSET rising (VTH - 100mV to
VTH + 100mV) 0.55 Fs
UVSET to GATE Propagation Delay tUVG VUVSET rising (VTH - 100mV to
VTH +100mV) 20 Fs
MAX16126/MAX16127
Maxim Integrated
2
Load-Dump/Reverse-Voltage Protection Circuits
Note 2: All parameters are production tested at TA = +25NC. 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.
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 12V, CGATE-SOURCE = 1nF, TA = -40NC to +125NC, unless otherwise noted. Typical values are at TA = +25NC.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
OVSET to FLAG Propagation Delay tOV VOVSET rising (VTH - 100mV to
VTH + 100mV) 0.3 Fs
GATE Output Voltage High Above
VSRC VOHGATE
VIN = VSRC = VOUT = 3V,
IGATE = -1FA4.3 4.7 6
V
VIN = VSRC = VOUT = 12V,
IGATE = -1FA6.25 7 8
GATE Pulldown Current IPD VGATE = 12V 8.8 mA
GATE Charge-Pump Current IGATE VIN = VGATE = VSRC = 12V 155 FA
Thermal Shutdown T++145 NC
Thermal Shutdown Hysteresis δT 15 NC
SHDN Logic-High Input Voltage VIH 1.4 V
SHDN Logic-Low Input Voltage VIL 0.4 V
SHDN Input Pulse Width tPW 6Fs
SHDN Input Pulldown Current ISPD 0.8 1.2 FA
FLAG Output Voltage Low VOL FLAG sinking 1mA 0.4 V
FLAG Leakage Current IIL VFLAG = 12V 0.5 FA
MAX16126/MAX16127
Maxim Integrated
3
Load-Dump/Reverse-Voltage Protection Circuits
Typical Operating Characteristics
(VIN = 12V, TA = +25NC, unless otherwise noted.)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX16126 toc01
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (µA)
302010
100
150
200
250
300
50
04
0
SHDN = HIGH
GATE ENHANCED
SUPPLY CURRENT vs. TEMPERATURE
MAX16126 toc02
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
120100-20 0 20 6040 80
170
190
210
230
250
270
290
310
150
-40
SHDN = HIGH
GATE ENHANCED
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX16126 toc03
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (µA)
2418126
20
30
40
50
60
70
80
90
100
10
03
0
SHDN = LOW
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
MAX16126 toc04
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
11095-25 -10 5 35 50 6520 80
15
20
25
30
35
40
45
50
10
-40 125
SHDN = LOW
SHDN PULLDOWN CURRENT
vs. TEMPERATURE
MAX16126 toc05
TEMPERATURE (°C)
SHDN PULLDOWN CURRENT (µA)
1109565 80-10 5 20 35 50-25
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0
-40 125
GATE TO SOURCE VOLTAGE
vs. SUPPLY VOLTAGE
MAX16126 toc06
SUPPLY VOLTAGE (V)
(VGATE - VSRC) (V)
21186 9 12 15
3
4
5
6
7
8
9
10
2
32
4
GATE-TO-SOURCE VOLTAGE
vs. TEMPERATURE
MAX16126 toc07
TEMPERATURE (°C)
(VGATE - VSRC) (V)
11095-25 -10 5 35 50 6520 80
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
4.0
-40 125
GATE ENHANCED
VIN = VSRC = VOUT
GATE PULLDOWN CURRENT
vs. TEMPERATURE
MAX16126 toc08
TEMPERATURE (°C)
GATE PULLDOWN CURRENT (mA)
8
11
14
17
20
5
11095-25 -10 535506520 80-40 125
VGATE = 12V
VSRC = GND
GATE PULLUP CURRENT
vs. SUPPLY VOLTAGE
MAX16126 toc09
SUPPLY VOLTAGE (V)
GATE PULLUP CURRENT (µA)
25205 10 15
135
140
145
150
155
160
165
170
130
03
0
VIN = VGATE = VSRC
GATE ENHANCED
MAX16126/MAX16127
Maxim Integrated
4
Load-Dump/Reverse-Voltage Protection Circuits
Typical Operating Characteristics (continued)
(VIN = 12V, TA = +25NC, unless otherwise noted.)
OVSET THRESHOLD vs. TEMPERATURE
MAX16126 toc10a
TEMPERATURE (°C)
OVSET THRESHOLD (V)
0.7
0.9
1.1
1.3
1.5
0.5
11095-25 -10 535506520 80-40 125
FALLING
RISING
UVSET THRESHOLD vs. TEMPERATURE
MAX16126 toc10b
TEMPERATURE (°C)
UVSET THRESHOLD (V)
0.7
0.9
1.1
1.3
1.5
0.5
11095-25 -10 535506520 80-40 125
FALLING
RISING
FLAG OUTPUT LOW VOLTAGE
vs. CURRENT
MAX16126 toc11
FLAG CURRENT (mA)
FLAG VOLTAGE (V)
1.51.00.5
0.1
0.2
0.3
0.4
0.5
0
02
.0
OVERVOLTAGE FAULT TO GATE
PROPAGATION DELAY vs. TEMPERATURE
MAX16126 toc12
TEMPERATURE (°C)
PROPAGATION DELAY (µs)
0.25
0.50
0.75
1.00
0
11095-25 -10 535506520 80-40 125
VOVSET PULSED FROM
(VTH - 100mV) TO (VTH + 100mV)
REVERSE CURRENT
vs. REVERSE VOLTAGE
MAX16126 toc13
REVERSE VOLTAGE (V)
REVERSE CURRENT (µA)
252015105
5
10
15
20
25
30
0
03
0
MAX16126/MAX16127
Maxim Integrated
5
Load-Dump/Reverse-Voltage Protection Circuits
Typical Operating Characteristics (continued)
(VIN = 12V, TA = +25NC, unless otherwise noted.)
STARTUP WAVEFORM
(VIN = 0 TO 12V, RL = 100I,
CIN = 0.1µF, COUT = 100µF)
MAX16126 toc14
VIN
10V/div
VGATE
10V/div
VOUT
10V/div
400µs/div
STARTUP FROM SHUTDOWN
(SHDN RISING 0 TO 2V, VIN = 12V,
RLOAD = 100I, CIN = 0.1µF)
MAX16126 toc15
VSHDN
2V/div
VGATE
10V/div
VOUT
10V/div
400µs/div
OVERVOLTAGE SWITCH FAULT
(VOV = 20V, CIN = 0.1µF, COUT = 100µF)
MAX16126 toc16
VIN
20V/div
VGATE
10V/div
VOUT
20V/div
100ms/div
OVERVOLTAGE LIMITER
(VUV = 4V, VOV = 20V,
CIN = 0.1µF, COUT = 100µF)
MAX16126 toc17
VIN
20V/div
VGATE
20V/div
VOUT
10V/div
20ms/div
MAX16126/MAX16127
Maxim Integrated
6
Load-Dump/Reverse-Voltage Protection Circuits
Pin Configuration
12
11
10
4
5
TERM
N.C.
6
I.C.
OUT
12
GATE
3
987
IN
GND
OVSET
UVSET
EP
SRC
TQFN
MAX16126
MAX16127
TOP VIEW
+
FLAG
SHDN
MAX16126/MAX16127
Maxim Integrated
7
Load-Dump/Reverse-Voltage Protection Circuits
Pin Description
PIN NAME FUNCTION
1SHDN Shutdown Input. Drive SHDN low to force GATE and FLAG low and turn off the external n-channel
MOSFETs. Connect a 100kI 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. No Connection. Not internally connected.
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 Ground
7 I.C. Internally Connected. Connect to GND.
8FLAG
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 100I series resistor. Bypass with a
minimum 10FF 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
0.1FF ceramic capacitor to GND.
— EP Exposed Pad. Can be connected to GND or left unconnected.
MAX16126/MAX16127
Maxim Integrated
8
Load-Dump/Reverse-Voltage Protection Circuits
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.
The devices feature an overvoltage and an undervoltage
comparator for voltage window detection. A flag output
(FLAG) asserts when a fault event occurs.
Two external back-to-back n-channel MOSFETs provide
reverse-voltage protection and also prevent reverse cur-
rent during a fault condition. Compared to a traditional
reverse-battery diode, this approach minimizes power
dissipation and voltage drop, and allows the circuit to
operate at very low cold-crank voltages (3V minimum).
The MAX16127 provides a limiter-mode fault manage-
ment for overvoltage and thermal shutdown conditions,
whereas the MAX16126 provides switch-mode fault
management for overvoltage and thermal shutdown con-
ditions. 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.
Gate Charge Pump
The MAX16126/MAX16127 use a charge pump to gener-
ate the GATE to SRC voltage and enhance the external
MOSFETs. After the input voltage exceeds the input
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 condi-
tions 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 regu-
lated 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 7V above
SRC. The output voltage is monitored through a resis-
tive 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 overvolt-
age 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 overvolt-
age 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.
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.
MAX16126/MAX16127
Maxim Integrated
9
Load-Dump/Reverse-Voltage Protection Circuits
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 undervolt-
age 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 tempera-
ture exceeds +145NC (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 = +145NC
(typ), the internal thermal sensor signals the shutdown
logic, pulling the GATE voltage low and allowing the
device to cool. When TJ drops by 15NC (typ), GATE goes
high and the MOSFETs turn back on. Do not exceed the
absolute maximum junction-temperature rating of TJ =
+150NC.
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.
TERM Connection
The TERM connection has an internal switch to IN. In
shutdown (SHDN = GND), this switch is open. By con-
necting 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 cur-
rent reduced.
Reverse-Voltage Protection
The MAX16126/MAX16127 integrate reverse-voltage
protection, preventing damage to the downstream cir-
cuitry caused by battery reversal or negative transients.
The devices can withstand reverse voltage to -30V
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
OUTPUT to GND, and minimize the parasitic capaci-
tance from GATE to GND to have a fast reserve-battery
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 protec-
tion diode.
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 ISO7637-2 specification.
Most of the pulses can be mitigated with capacitors
and zener clamp diodes (see the Typical Operating
Characteristics and also the Increasing the Operating
Voltage 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 regula-
tion 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 characteris-
tics 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 val-
ues from the ISO7637-2 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 volt-
age 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 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.
MAX16126/MAX16127
Maxim Integrated
10
Load-Dump/Reverse-Voltage Protection Circuits
Table 1. Summary of ISO7637 Pulses
Refer to the ISO7637-2 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 over-
voltage 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:
TOTAL
TRIPLOW TH TH-HYS
R
V (V - V ) R2 R3
=
+
TOTAL
TRIPHIGH TH
R
VV
R3
=
where RTOTAL = R1 + R2 + R3, VTH is the 1.225V OVSET/
UVSET threshold, 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:
TH TOTAL
TRIPHIGH
VR
R3 V
×
=
3) Calculate R2 based on RTOTAL, R3, and the desired
lower trip point:
TH TH-HYS TOTAL
TRIPLOW
(V - V ) R
R2 - R3
V
×
=
4) Calculate R1 based on RTOTAL, R2, and R3:
TOTAL
R1 R - R2 - R3=
*Relative to system voltage.
NAME DESCRIPTION PEAK VOLTAGE (V) (max)*DURATION
12V SYSTEM
Pulse 1 Inductive load disconnection -100 1ms to 2ms
Pulse 2a Inductive wiring disconnection 50 0.05ms
Pulse 3a Switching transients -150 0.2Fs
Pulse 3b 100
Pulse 4 Cold crank -7 100ms (initial)
-6 Up to 20s
Pulse 5a Load dump (unsuppressed) 87 400ms (single)
Pulse 5b Load dump (suppressed) (Varies, but less than pulse 5a)
MAX16126/MAX16127
Maxim Integrated
11
Load-Dump/Reverse-Voltage Protection Circuits
Setting Overvoltage and Undervoltage
Thresholds (MAX16127)
The MAX16127 operates in limiter mode and uses sepa-
rate resistive dividers to set the undervoltage and over-
voltage 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:
TOTAL_OV
TH OV
R
R4 V V
= ×
where RTOTAL_UV = 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:
TOTAL_UV
TH TH-HYS UV
R
R2 (V - V ) V
= ×
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 resis-
tance dissipates more power, but provides slightly better
accuracy.
MOSFET Selection
MOSFET selection is critical to design a proper protec-
tion 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 num-
ber. 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.
Figure 1. Overvoltage and Undervoltage Window Detector Circuit (MAX16126)
GND
GATE
VIN
100kI
10nF
SRC OUT
IN OUT
DC-DC
CONVERTER
SHDN
TERM
IN
UVSET
OVSET
GND
R1
R2
R3
MAX16126
0.1µF
FLAG
10µF
100I
MAX16126/MAX16127
Maxim Integrated
12
Load-Dump/Reverse-Voltage Protection Circuits
MOSFET Power Dissipation
The RDS(ON) must be low enough to limit the MOSFET
power dissipation during normal operation. Power dis-
sipation (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 impos-
es 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
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.
Figure 2. Overvoltage and Undervoltage Limiter Protection Configuration (MAX16127)
GND
GATE
VIN
100kI
SRC
IN OUT
DC-DC
CONVERTER
100I
SHDN
IN OUT
TERM
OVSET
UVSET
GND
R3
R4
R1
R2
MAX16127
10nF
0.1µF
FLAG
10µF
MAX16126/MAX16127
Maxim Integrated
13
Load-Dump/Reverse-Voltage Protection Circuits
Increasing the Operating Voltage Range
The MAX16126/MAX16127 can tolerate -30V to +90V. To
increase the voltage range, connect two back-to-back
zener diodes from IN to GND, and connect a resistor in
series with IN and the power-supply input to limit the cur-
rent 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 clamp-
ing the low-energy ISO7637-2 pulses.
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 shutdown input needs a series resistor to limit the
current if VIN exceeds the clamped voltage on IN. A good
starting point is 100kI.
Output Reservoir Capacitor
The output capacitor can be used as a reservoir capaci-
tor 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.
Figure 3. Circuit to Increase Operating Voltage Range
GND
GATE
VBATT
SRC OUT
IN OUT
DC-DC
CONVERTER
SHDN
IN
GND
D1
D2
RS
100kI
MAX16126
MAX16127
100kI
0.1µF FLAG
100I
10µF
10nF
MAX16126/MAX16127
Maxim Integrated
14
Load-Dump/Reverse-Voltage Protection Circuits
Figure 4. MAX16126 Typical Operating Circuit
GATE
VIN
R1
R2
R3
100kI
SRC OUT
VOUT
COUT
10µF
SHDN
TERM
IN
UVSET
OVSET
GND
MAX16126 FLAG
100I
0.1µF
10nF
MAX16126/MAX16127
Maxim Integrated
15
Load-Dump/Reverse-Voltage Protection Circuits
Figure 5. MAX16127 Typical Operating Circuit
GATE
VIN
100kI
SRC OUT
VOUT
SHDN
OVSET
R1
R3
R4
R2
TERM
IN
UVSET
GND
MAX16127
FLAG
100I
0.1µF
10nF 10µF
MAX16126/MAX16127
Maxim Integrated
16
Load-Dump/Reverse-Voltage Protection Circuits
Figure 6. MAX16126/MAX16127 Functional Diagram
1.225V
SHDN
POWER-OK
CHARGE
PUMP
OUT
SRCGATE
CONTROL LOGIC
UVLO
1.225V
FLAG
UVSET
OVSET
TERM
IN
THERMAL
PROTECTION
GND
MAX16126
MAX16127
MAX16126/MAX16127
Maxim Integrated
17
Load-Dump/Reverse-Voltage Protection Circuits
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.
Chip Information
PROCESS: BiCMOS
Ordering Information
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
Note: All devices are specified over the -40°C to +125°C temperature range.
PART PIN-PACKAGE TOP MARK FUNCTION
MAX16126TCA+ 12 TQFN-EP* +ABV
Switch mode
Always autoretry
MAX16126TCB+ 12 TQFN-EP* +ABX One retry, then latch
MAX16126TCC+ 12 TQFN-EP* +ABY Three retries, then latch
MAX16126TCD+ 12 TQFN-EP* +ABZ Latch mode
MAX16127TC+ 12 TQFN-EP* +ABW Limiter mode
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
12 TQFN-EP T1233+4 21-0136 90-0019
MAX16126/MAX16127
Maxim Integrated
18
Load-Dump/Reverse-Voltage Protection Circuits
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 11/11 Initial release —
MAX16126/MAX16127
Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000
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.
© Maxim Integrated The Maxim logo and Maxim Integrated are trademarks of Maxim Integrated Products, Inc.
