A3921: Automotive Full Bridge MOSFET Driver


The A3921 is a full-bridge controller for use with external N-channel power MOSFETs and is specifically designed for automotive applications with high-power inductive loads, such as brush DC motors.

A unique charge pump regulator provides full (>10 V) gate drive for battery voltages down to 7  V and allows the A3921 to operate with a reduced gate drive, down to 5.5 V. A bootstrap capacitor is used to provide the above-battery supply voltage required for N-channel MOSFETs. An internal charge pump for the high-side drive allows DC (100% duty cycle) operation.

The full bridge can be driven in fast or slow decay modes using diode or synchronous rectification. In the slow decay mode, current recirculation can be through the high-side or the lowside FETs. The power FETs are protected from shoot-through by resistor adjustable dead time.

Integrated diagnostics provide indication of undervoltage, overtemperature, and power bridge faults, and can be configured to protect the power MOSFETs under most short circuit conditions.

The A3921 is supplied in a 28-pin TSSOP power package with an exposed thermal pad (suffix LP). This package is lead (Pb) free, with 100% matte tin leadframe plating.

Top Features

  • High current gate drive for N-channel MOSFET full bridge
  • High-side or low-side PWM switching
  • Charge pump for low supply voltage operation
  • Top-off charge pump for 100% PWM
  • Cross-conduction protection with adjustable dead time
  • 5.5 to 50 V supply voltage range
  • Integrated 5 V regulator
  • Diagnostics output
  • Low current sleep mode

Part Number Specifications and Availability

Part Number Package Type Temperature RoHS
Part Composition /
RoHS Data
Comments Samples Check Stock
APEK3921KLP-01-T DEMO BOARD -20°C to 85°C No -- Contact your
local sales rep
Distributor Stock
A3921KLPTR-T 28-lead TSSOP -40°C to 125°C Yes View Data Contact your
local sales rep
Distributor Stock

Allegro’s products are not to be used in any devices or systems, including but not limited to life support devices or systems, in which a failure of Allegro’s product can reasonably be expected to cause bodily harm.



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