MAX16128 Datasheet, PDF (8/15 Pages) Maxim Integrated Products – Load-Dump/Reverse-Voltage Protection Circuits

MAX16128/MAX16129
Load-Dump/Reverse-Voltage Protection Circuits
Detailed Description
The MAX16128/MAX16129 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
current during a fault condition. Compared to a traditional
reverse-battery diode, this approach minimizes power
dissipation and voltage drop.
The MAX16129 provides a limiter-mode fault manage-
ment for overvoltage and thermal-shutdown conditions,
whereas the MAX16128 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 devices use a charge pump to generate 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
an 8.8mA (min) pulldown current. Note that an exter-
nal zener diode is required to be connected between
the gate and source of the external MOSFETs (see the
Applications Information section).
Overvoltage Protection
The devices detect overvoltage conditions using a com-
parator that is connected through an internal 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 (MAX16129)
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 9V above
SRC. The output voltage is monitored through an internal
resistive divider. 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
MAX16129 in voltage-limiting mode for long durations.
Since MOSFETs can dissipate power continuously during
this interval, proper heatsinking should be implemented
to prevent damage to them.
Overvoltage Switch (MAX16128)
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 MAX16128 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.
Maxim Integrated
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