MAX16128 Datasheet, PDF (9/15 Pages) Maxim Integrated Products – Load-Dump/Reverse-Voltage Protection Circuits

MAX16128/MAX16129
Load-Dump/Reverse-Voltage Protection Circuits
Undervoltage Protection
The devices monitor the input voltage for undervoltage
conditions. If the input voltage is below the undervoltage
threshold (V_IN < V_UV-TH - V_UV-HYS), GATE goes low,
turning off the external MOSFETs and FLAG asserts.
When the input voltage exceeds the undervoltage thresh-
old (V_IN > V_{UV_TH}), GATE goes high after a 150Fs delay
(typ).
For the MAX16128/MAX16129, the undervoltage thresh-
old is determined by the part number suffix option (see
Table 2).
Cold-Crank Monitoring
Cold-crank faults occur when the input voltage decreas-
es from its steady-state condition. A cold-crank com-
parator monitors IN through an internal resistive divider.
The MAX16128/MAX16129 offer two ways to handle this
kind of fault depending on a part number suffix (see the
Selector Guide):
• The cold-crank comparator is disabled and external
MOSFETs stay on during the falling input-voltage
transient unless the input voltage falls below the
undervoltage threshold (see Table 2).
• The cold-crank comparator is enabled and external
MOSFETs are switched off by pulling down GATE if
the input voltage falls below the cold-crank threshold
to avoid load discharge due to reverse current from
OUT to IN (see Table 4).
In the last case, cold-crank protection is enabled as long
as V_OUT is higher than 90% of V_IN (with a 3% hysteresis)
and V_IN is higher than the undervoltage threshold. When
the monitored input voltage falls below the falling cold-
crank fault threshold (V_IN < V_CCK), the GATE is pulled
down and FLAG is asserted low. When the input voltage
rises back above the rising cold-crank fault threshold
(V_IN > V_CCK + V_{CLK_HYS}), FLAG is released and the
charge pump enhances GATE above SRC, reconnecting
the load to the input.
Thermal Shutdown
The devices’ thermal-shutdown feature turns off the
MOSFETs if the internal die temperature exceeds 145NC
(T_J). By ensuring good thermal coupling between the
MOSFETs and the devices, the thermal shutdown can
turn off the MOSFETs if they overheat.
When the junction temperature exceeds T_J = +145NC
(typ), the internal thermal sensor signals the shutdown
logic, pulling the GATE voltage low and allowing the
device to cool. When T_J drops by 15NC (typ), GATE goes
Maxim Integrated
high and the MOSFETs turn back on. Do not exceed the
absolute maximum junction-temperature rating of T_J =
+150NC.
Flag Output (FLAG)
An open-drain FLAG output indicates fault conditions.
During startup, FLAG is initially low and goes high imped-
ance when V_OUT is greater than 90% of V_IN if no fault
conditions are present. FLAG asserts low during shut-
down mode, an overvoltage, thermal shutdown, or under-
voltage fault, or when V_OUT falls below 90% of V_IN. In the
versions where the cold-crank comparator is enabled,
FLAG asserts low during a cold-crank fault.
Reverse-Voltage Protection
The devices integrate reverse-voltage protection, pre-
venting damage to the downstream circuitry caused
by battery reversal or negative transients. The devices
can withstand reverse voltage to -6V without damage to
themselves or the load. During a reverse-voltage condi-
tion, the two external n-channel MOSFETs are turned off,
protecting the load. Connect a 0.1FF ceramic capacitor
from IN to GND, connect a 10nF ceramic capacitor from
GATE to SRC, connect a 10FF capacitor from OUT to
GND, and minimize the parasitic capacitance from GATE
to GND to have fast reverse-battery voltage-transient
protection. During normal operation, both MOSFETs are
turned on and have a minimal forward-voltage drop, pro-
viding lower power dissipation and a much lower voltage
drop than a reverse-battery protection 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 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 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-
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