a4982 Allegro MicroSystems, Inc., a4982 Datasheet - Page 10

• Manufacturer Part Number: a4982
• Description: Dmos Microstepping Driver With Translator And Overcurrent Protection
• Manufacturer: Allegro MicroSystems, Inc.

A4982
Sleep Mode
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 A4982
into Sleep mode. A logic high allows normal operation, as well as
start-up (at which time the A4982 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.
Mixed Decay Operation.
decay mode, at power-on and reset, and during normal running
according to the ROSC configuration and the step sequence, as
shown in figures 3 through 6. During Mixed decay, when the trip
point is reached, the A4982 initially goes into a fast decay mode
for 31.25% of the off-time, t
decay mode for the remainder of t
feature appears in figure7.
Typically, mixed decay is only necessary when the current in the
winding is going from a higher value to a lower value as determined
by the state of the translator. For most loads automatically-selected
mixed decay is convenient because it minimizes ripple when the cur-
rent is rising and prevents missed steps when the current is falling.
For some applications where microstepping at very low speeds is
necessary, the lack of back EMF in the winding causes the current to
increase in the load quickly, resulting in missed steps. This is shown
in figure 2. By pulling the ROSC pin to ground, mixed decay is set
to be active 100% of the time, for both rising and falling currents,
and prevents missed steps as shown in figure 3. If this is not an issue,
it is recommended that automatically-selected mixed decay be used,
because it will produce reduced ripple currents. Refer to the Fixed
Off-Time section for details.
Synchronous Rectification
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
diodes with the low FET R
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.
( ¯ S ¯ ¯ L ¯ ¯ E ¯ ¯ E ¯ ¯ P ¯ ). To minimize power consumption
DS(ON)
OFF
The bridge operates in Mixed
. After that, it switches to Slow
. This reduces power dissipation
OFF
. When a PWM-off cycle is
. A timing diagram for this
DMOS Microstepping Driver with Translator
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
and Overcurrent Protection
5 A / div.
5 A / div.
5 A / div.
Fast decay portion
(direction change)
Fixed off-time
Fixed off-time
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
t →
t →
t →
Fault
latched
10