7

26184.29A

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

115 Northeast Cutoff, Box 15036

www.allegromicro.com

Allegro MicroSystems, Inc.

A3983

DMOS Microstepping Driver with Translator

30 μs. The ROSC pin can be safely connected to the VDD

sense comparators when the outputs are switched by the

internal current control circuitry. The comparator outputs are

blanked to prevent false overcurrent detection due to reverse

recovery currents of the clamp diodes, and switching tran-

sients related to the capacitance of the load. The blank time,

used to generate a gate supply greater than that of VBB

for driving the source-side DMOS gates. A 0.1 μF ceramic

capacitor, should be connected between CP1 and CP2. In

addition, a 0.1 μF ceramic capacitor is required between

VCP and VBB, to act as a reservoir for operating the

high-side DMOS gates.

to operate the sink-side DMOS outputs. The VREG pin must

be decoupled with a 0.22 μF ceramic capacitor to ground.

VREG is internally monitored. In the case of a fault condi-

tion, the DMOS outputs of the A3983 are disabled.

the DMOS 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,

MS1, and MS2, as well as the internal sequencing logic, all

remain active, independent of the ENABLE input state.

puts of the A3983 are disabled until the fault condition is

removed. At power-on, the UVLO (undervoltage lockout)

circuit disables the DMOS 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 DMOS FETs, current

regulator, and charge pump. A logic low on the SLEEP pin

puts the A3983 into Sleep mode. A logic high allows normal

operation, as well as start-up (at which time the A3983 drives

the motor to the Home microstep position). When emerging

from Sleep mode, in order to allow the charge pump to stabi-

lize, provide a delay of 1 ms before issuing a Step command.

Mixed Decay mode, depending on the step sequence, as

shown in figures 3 thru 5. As the trip point is reached, the

A3983 initially goes into a fast decay mode for 31.25% of

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

recirculates according to the decay mode selected by the

control logic. This synchronous rectification feature turns on

the appropriate FETs during current decay, and effectively

reduces power dissipation significantly, and can eliminate

the need for external Schottky diodes in many applications.

Turning off synchronous rectification prevents the reversal of

the load current when a zero-current level is detected.