A3952SW datasheet(10/16 Pages) ALLEGRO

10 / 16 page

3952

FULL-BRIDGE

PWM MOTOR DRIVER

115 Northeast Cutoff, Box 15036

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

Typical DC Servo Motor Application

µF

VBB

LOGIC

Dwg. EP-047

MODE

PHASE

ENABLE

BRAKE

+5 V

motor is more linear than in the case of ENABLE PWM

control (which produces a discontinuous current at low-

current levels).

With bidirectional dc servo motors, the PHASE termi-

nal can be used for mechanical direction control. Similar

to when braking the motor dynamically, abrupt changes in

the direction of a rotating motor produce a current gener-

ated by the back EMF. The current generated will depend

on the mode of operation. If the internal current-control

circuitry is not being used, then the maximum load current

generated can be approximated by

LOAD = (VBEMF + VBB)/RLOAD

where V

BEMF is proportional to the motor’s speed.

If the

internal slow-decay current-control circuitry is used, then

the maximum load current generated can be approximated

by I

LOAD = VBEMF/RLOAD. For both cases, care must be taken

to ensure the maximum ratings of the device are not

exceeded. If the internal fast-decay current-control

circuitry is used, then the load current will regulate to a

value given by

LOAD = VREF/(10•RS).

CAUTION: In fast-decay mode, when the direction of

the motor is changed abruptly, the kinetic energy stored in

the motor and load inertia will be converted into current

that charges the V

BB supply bulk capacitance (power

supply output and decoupling capacitance). Care must be

taken to ensure the capacitance is sufficient to absorb the

energy without exceeding the voltage rating of any devices

connected to the motor supply.

See also, the sections on brake operation under

“Functional Description,” above.

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