MAX16126 Datasheet, PDF(13/19 Page) Maxim Integrated Products – Load-Dump/Reverse-Voltage Protection Circuits

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MAX16126/MAX16127

Load-Dump/Reverse-Voltage Protection Circuits

VIN

10nF

0.1ÂµF

100kI

GATE

SHDN

TERM

UVSET

SRC

MAX16127

GND

100I

OUT

DC-DC

CONVERTER

OUT

10ÂµF

GND

FLAG

OVSET

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 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.

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