DMOS Microstepping Driver with Translator

and Overcurrent Protection

A4988

10

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

4988-DS

operate the sink-side FET outputs. The VREG pin must be

internally monitored. In the case of a fault condition, the FET

outputs of the A4988 are disabled.

Capacitor values should be Class 2 dielectric ±15% maximum,

or tolerance R, according to EIA (Electronic Industries Alliance)

specifications.

FET outputs. When set to a logic high, the outputs are disabled.

When set to a logic low, the internal control enables the outputs

as required. The translator inputs STEP, DIR, and MSx, as well as

the internal sequencing logic, all remain active, independent of the

¯E¯¯N¯¯A¯¯B¯¯L¯¯E¯ input state.

or an undervoltage (on VCP), the FET outputs of the A4988 are

disabled until the fault condition is removed. At power-on, the

UVLO (undervoltage lockout) circuit disables the FET outputs

and resets the translator to the Home state.

when the motor is not in use, this input disables much of the

internal circuitry including the output FETs, current regulator,

and charge pump. A logic low on the S¯¯L¯¯E¯¯E¯¯P¯ pin puts the A4988

into Sleep mode. A logic high allows normal operation, as well as

start-up (at which time the A4988 drives the motor to the Home

microstep position). When emerging from Sleep mode, in order

to allow the charge pump to stabilize, provide a delay of 1 ms

before issuing a Step command.

Decay mode, depending on the step sequence, as shown in fig-

ures 8 through 12. As the trip point is reached, the A4988 initially

After that, it switches to Slow Decay mode for the remainder of

triggered by an internal fixed-off time cycle, load current recircu-

lates according to the decay mode selected by the control logic.

This synchronous rectification feature turns on the appropriate

FETs during current decay, and effectively shorts out the body

significantly, and can eliminate the need for external Schottky

diodes in many applications. Synchronous rectification turns off

when the load current approaches zero (0 A), preventing reversal

of the load current.

t

→

Fixed off-time

5 A / div.

t

→

5 A / div.

Figure 4. Short-to-ground event

Figure 5. Shorted load (OUTxA

→ OUTxB) in

Slow decay mode

Figure 6. Shorted load (OUTxA

→ OUTxB) in

Mixed decay mode

Fixed off-time

Fast decay portion

(direction change)

t

→

5 A / div.

Fault

latched