MAX16126 Datasheet, PDF(10/19 Page) Maxim Integrated Products – Load-Dump/Reverse-Voltage Protection Circuits

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MAX16126/MAX16127

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

0.1ÂµF ceramic capacitor from IN to GND, connect a 10nF

ceramic capacitor from GATE to SRC, connect 10ÂµF 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.

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