TLH8679

August 1992

LM621 Brushless Motor Commutator

General Description

The LM621 is a bipolar IC designed for commutation of

brushless DC motors The part is compatible with both

three- and four-phase motors It can directly drive the power

switching devices used to drive the motor The LM621 pro-

vides an adjustable dead-time circuit to eliminate ‘‘shoot-

through’’ current spiking in the power switching circuitry

Operation is from a 5V supply but output swings of up to

40V are accommodated The part is packaged in an 18-pin

dual-in-line package

Features

Y

Adjustable dead-time feature eliminates current spiking

Y

On-chip clock oscillator for dead-time feature

Y

Outputs drive bipolar power devices (up to 35 mA base

current) or MOSFET power devices

Y

Compatible with three- and four-phase motors

Bipolar drive to delta- or Y-wound motors

Unipolar drive to center-tapped Y-wound motors

Supports 30- and 60-degree shaft position sensor

placements for three-phase motors

Supports 90-degree sensor placement for four-phase

motors

Y

Directly interfaces to pulse-width modulator output(s)

via OUTPUT INHIBIT (PWM magnitude) and DIREC-

TION (PWM sign) inputs

Y

Direct interface to Hall sensors

Y

Outputs are current limited

Y

Undervoltage lockout

Connection Diagram

TLH8679 – 1

Order Number LM621N

See NS Package Number N18A

C1995 National Semiconductor Corporation

RRD-B30M115Printed in U S A