A3977KLP datasheet(8/18 Pages) ALLEGRO

8 / 18 page

115 Northeast Cutoff, Box 15036

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

3977

MICROSTEPPING DMOS DRIVER

WITH TRANSLATOR

Synchronous Rectification. When a PWM off cycle

is triggered by an internal fixed off-time cycle, load

current will recirculate according to the decay mode

selected by the control logic. The A3977 synchronous

rectification feature will turn on the appropriate

MOSFETs during the current decay and effectively short

out the body diodes with the low rDS(on) driver. This will

reduce power dissipation significantly and eliminate the

need for external Schottky diodes for most applications.

The synchronous rectification can be set in either

active mode or disabled mode.

Functional Description (cont’d)

Active Mode. When the SR input is logic low, active

mode is enabled and synchronous rectification will occur.

This mode prevents reversal of the load current by turning

off synchronous rectification when a zero current level is

detected. This prevents the motor winding from conduct-

ing in the reverse direction.

Disabled Mode. When the SR input is logic high,

synchronous rectification is disabled. This mode is

typically used when external diodes are required to

transfer power dissipation from the A3977 package to the

external diodes.

Timing Requirements

(TA = +25°C, VDD = 5 V, Logic Levels are VDD and Ground)

50%

STEP

MS1/MS2/

DIR/RESET

Dwg. WP-042

SLEEP

A. Minimum Command Active Time

Before Step Pulse (Data Set-Up Time) ..... 200 ns

B. Minimum Command Active Time

After Step Pulse (Data Hold Time) ............ 200 ns

C. Minimum STEP Pulse Width ...................... 1.0

µs

D. Minimum STEP Low Time ......................... 1.0

µs

E. Maximum Wake-Up Time ......................... 1.0 ms

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