2916 データシートの表示（PDF） - Allegro MicroSystems

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2916

DUAL FULL-BRIDGE PWM MOTOR DRIVER

Allegro MicroSystems 

2916

DUAL FULL-BRIDGE

MOTOR DRIVER

APPLICATIONS INFORMATION

PWM CURRENT CONTROL

The UDN2916B/EB/LB dual bridges are designed to

drive both windings of a bipolar stepper motor. Output

current is sensed and controlled independently in each

bridge by an

parator, and

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internal

com-

PWM OUTPUT CURRENT WAVE FORM

V PHAS E

When the bridge is turned ON, current increases in

the motor winding and it is sensed by the external sense

resistor until the sense

set at the comparator’s

voltage

input:

(VSENSE)

reaches

the

level

ITRIP = VREF/10 RS

The comparator then triggers the monostable which

turns OFF the source driver of the bridge. The actual

load current peak will be slightly higher than the trip point

(especially for low-inductance loads) because of the

internal logic and switching

typically 2 µs. After turn-off,

dtheelamyso.toTrhcisurdreenlatyd(etdc)aiyss,

circulating through the ground-clamp diode and sink

transistor. The source driver’s OFF time (and therefore

the magnitude of the current decrease) is determined by

the monostable’s external RC timing components, where

toff = RTCT within the range of 20 kΩ to 100 kΩ and

100 pF to 1000 pF.

The fixed-off time should be short enough to keep

the current chopping above the audible range (< 46 µs)

and long enough to properly regulate the current. Be-

cause only slow-decay current control is available, short

off times (< 10 µs) require additional efforts to ensure

proper current regulation. Factors that can negatively

affect the ability to properly regulate the current when

using short off times include: higher motor-supply volt-

age, light load, and longer than necessary blank time.

When the source driver is re-enabled, the winding

current (the sense voltage) is again allowed to rise to the

comparator’s threshold. This cycle repeats itself, main-

taining the average motor winding current at the desired

level.

+

I OUT 0

–

ITR IP

td

toff

Dwg. WM-003-1A

LOAD CURRENT PATHS

VB B

Loads with high distributed capaci-tances may

result in high turn-ON current peaks. This peak (appear-

ing

ing

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otoscfuilrlathtieorndse. laAyntehxetearcntiaolnRoCfCthC etimcoemdpealaraytsohr.ouDldepbeenudsinegd

on load type, many applications will not require these

external components (SENSE connected to E).

BR IDGE ON

RS

S OUR CE OFF

ALL OFF

Dwg. E P -006-1

4

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

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