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2

SA53U

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

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 dynamically

from the system controller. This technique

essentially reduces the current limit thresh-

old voltage to (Vth-VDAC). During expect-

ed conditions of high torque demand, such

as start-up or reversal, the DAC can adjust

the current limit dynamically to allow pe-

riods of high current. In normal operation

when low current is expected, the DAC

output voltage can increase, reducing the

current limit setting to provide more con-

servative fault protection.

2.6ExTERNALFLYBACK

DIODES

External fly-back diodes will offer superior

reverse recovery characteristics and low-

er forward voltage drop than the internal

back-body diodes. In high current applica-

tions, external flyback diodes can reduce power dissipation and heat-

ing during commutation of the motor current. Reverse recovery time

and capacitance are the most important parameters to consider when

selecting these diodes. Ultra-fast rectifiers offer better reverse recovery

time and Schottky diodes typically have low capacitance. Individual ap-

plication requirements will be the guide when determining the need for

these diodes and for selecting the component which is most suitable.

It INPUT

OUT 1

I1

V

th

I

FiGURE 8. CURRENT LimiT WAVEFORmS

FIgURE9.SChOTTKYDIODES

OUT 1

OUT 2

V

S

V

S

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