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3932

THREE-PHASE POWER MOSFET CONTROLLER

internal fixed off time PWM control circuit. When the

outputs of the MOSFETs are turned on, current increases in

the motor winding until it reaches a value given by:

At the trip point, the sense comparator resets the source

enable latch, turning off the source driver. At this point, load

inductance causes the current to recirculate for the fixed off

time period. The current path during recirculation is

determined by the configuration of the MODE and SR input

pins. The fixed off time is determined by an external resistor

terminal to AGND. The fixed off time is approximated by:

Torque control can be implemented by varying the REF

input voltage as long as the PWM input stays high. If direct

control of the torque/current is desired by PWM input, a

voltage can be applied to the REF pin to set an absolute

maximum current limit.

to set the BLANK time duration. At the end of a PWM off

cycle, a high side gate selected by the commutation logic will

turn on. At this time, large current transients can occur

during the reverse recovery time (trr) of the intrinsic body

diodes of the power MOSFETs. To prevent false tripping of

the sense comparator, the blank function will disable the

comparator for a time defined by:

current spike duration.

sink side MOSFETs on, and all source side MOSFETs off.

This will effectively short out the BEMF and brake the

motor. During braking the load current can be approximated

by:

As the current does not flow through the sense resistor

during a dynamic brake, care should be taken to ensure that

the power MOSFETs maximum ratings are not exceeded.

The RESET pin overrides the BRAKE input. RESET will

always drive all gate outputs Low.