SA303

2

SA303U

P r o d u c t I n n o v a t i o n F r o m

The current limit feature may be disabled

by tying the I

current sense pins will continue to provide

top FET output current information.

Typically, the current sense pins source

current into grounded resistors which pro-

vide voltages to the current limit compara-

tors. If instead the current limit resistors

are connected to a voltage output DAC,

the current limit can be controlled dynami-

cally from the system controller. This tech-

nique essentially reduces the current limit

threshold voltage to (Vth-VDAC). During

expected conditions of high torque de-

mand, such as start-up or reversal, the

DAC can adjust the current limit dynami-

cally to allow periods of high current. In

normal operation when low current is ex-

pected, the DAC output voltage can in-

crease, reducing the current limit setting

to provide more conservative fault protec-

tion.

2.6ExTERNALFLYBACK

DIODES

External fly-back diodes will offer superior reverse recovery character-

istics and lower forward voltage drop than the internal back-body di-

odes. In high current applications, external flyback diodes can reduce

power dissipation and heating during commutation of the motor current.

Reverse recovery time and capacitance are the most important param-

eters to consider when selecting these diodes. Ultra-fast rectifiers offer

better reverse recovery time and Schottky diodes typically have low

capacitance. Individual application requirements will be the guide when

determining the need for these diodes and for selecting the component

which is most suitable.

A

OUTA

Ia

V

th

I

FiGURE 8. CURRENT LimiT WAVEFORmS

FIgURE9.SChOTTKY

DIODES

OUTA

OUTC

OUTB

V

S

V

S

V

S

SA303