2916

DUAL FULL-BRIDGE

MOTOR DRIVER

www.allegromicro.com

5

LOGIC CONTROL OF OUTPUT CURRENT

Two logic level inputs (l

winding current at 100%, 67%, 33%, or 0% of the maximum level per

the table. The 0% output current condition turns OFF all drivers in the

bridge and can be used as an OUTPUT ENABLE function.

CURRENT-CONTROL TRUTH TABLE

l

0

I

1

Output Current

LL

V

HL

V

LH

V

HH

0

These logic level inputs greatly enhance the implementation of

µP-controlled drive formats.

During half-step operations, the l

motor at a constant torque between all positions in an eight-step

TYPICAL APPLICATION

sequence. This is accomplished by digitally

selecting 100% drive current when only one

phase is ON and 67% drive current when two

phases are ON. Logic highs on both l

turn OFF all drivers to allow rapid current

decay when switching phases. This helps to

ensure proper motor operation at high step

rates.

The logic control inputs can also be

used to select a reduced current level (and

reduced power dissipation) for ‘hold’ condi-

tions and/or increased current (and available

torque) for start-up conditions.

GENERAL

The PHASE input to each bridge

determines the direction motor winding

current flows. An internally generated

deadtime (approximately 2 µs) prevents

crossover currents that can occur when

switching the PHASE input.

All four drivers in the bridge output can

be turned OFF between steps (l

resulting in a fast current decay through the

internal output clamp and flyback diodes. The

fast current decay is desirable in half-step and

high-speed applications. The PHASE, l

inputs float high.

Varying the reference voltage (V

provides continuous control of the peak load

current for micro-stepping applications.

Thermal protection circuitry turns OFF

all drivers when the junction temperature

reaches +170°C. It is only intended to protect

the device from failures due to excessive

junction temperature and should not imply

that output short circuits are permitted. The

output drivers are re-enabled when the

junction temperature cools to +145°C.

The UDN2916B/EB/LB output drivers

are optimized for low output saturation

voltages—less than 1.8 V total (source plus

sink) at 500 mA. Under normal operating

conditions, when combined with the excellent

thermal properties of the batwing package

design, this allows continuous operation of

both bridges simultaneously at 500 mA.

FROM

µP

V

REF

Dwg. EP-008B1

V

BB

FROM

µP

1

2

3

4

5

6

7

8

9

24

23

22

21

20

19

18

17

16

15

14

13

12

11

10

9

2

1

V

REF

+5 V

STEPPER

MOTOR

C

T

C

C

+

820 pF

56 kΩ

820 pF

56 kΩ