AP74502Q, AP74502HQ

Document number: DS47093 Rev. 1 - 2

13 of 22

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April 2025

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AP74502Q, AP74502HQ

, AP

Application Information

The AP74502Q, AP74502HQ is used with N-Channel MOSFET controller in a typical reverse polarity protection application. The schematic for the

12V battery protection application is shown below where the AP74502Q, AP74502HQ is used to drive back-to-back connected MOSFETs Q1 and

Q2 in series with a battery for reverse polarity protection and load disconnection. The TVS is required for protection for the AP74502Q, AP74502HQ

and its downstream application against positive and negative voltage surges and ESD event. Output Capacitor is recommended for filtering out

supply upon dynamic load condition.

Typical Application

AP74502(H)Q

GATE

SRC

OVLO

VCAP

GND

Voltage

Regulator

(DC/DC, LDO)

Q1

220uF

Battery /

Power

Source

VI N

R1

R2

EN/UVLO

ON

OFF

Q2

Design Example

Design Parameter

Example Value

VIN Range

12V Vehicle Battery, 12V nominal with 3.2V cold crank and 35V load dump condition

VOUT

3.2V during cold crank to 35V load dump

IOUT

3A nominal and 5A maximum

COUT

220

μF typical hold up Capacitor

Overvotlage Protection

Typical 37V for 12V battery system

Automotive EMC Compliance

ISO 7637-2 and ISO 16750-2

MOSFET Selection

The important MOSFET electrical parameters are the maximum continuous drain current, ID, the maximum drain-to-source voltage, VDS(MAX), the

maximum source current through body diode, and the drain-to-source on resistance, RDS(ON).

The maximum continuous drain current, ID, rating must exceed the maximum continuous load current. The maximum drain-to-source voltage,

VDS(MAX), must be high enough to withstand the highest differential voltage seen in the application. This would include any anticipated fault conditions.

It is recommended to use MOSFETs with voltage rating up to 75V maximum with the AP74502Q, AP74502HQ. The maximum VGS the AP74502Q,

AP74502HQ can drive is 13.9V, so a MOSFET with 15V minimum VGS rating must be selected. If a MOSFET with VGS rating < 15V is selected, a

Zener diode can be used to clamp VGS to safe level within Max VGS of the MOSFET.

To reduce the MOSFET conduction losses, lowest possible RDS(ON) is preferred. Selecting a MOSFET with RDS(ON) that gives VDS drop 20mV to 50

mV at full load provides good trade off in terms of power dissipation and cost. Thermal resistance of the MOSFET must be considered against the

expected maximum power dissipation in the MOSFET to ensure that the junction temperature (TJ) is well controlled.

220μF