A4987SLPTR-T View Datasheet(PDF) - Allegro MicroSystems
Part Name
Description
MFG CO.
A4987SLPTR-T
Allegro MicroSystems
'A4987SLPTR-T' PDF : 16 Pages View PDF
A4987
DMOS Dual Full-Bridge PWM Motor Driver
with Overcurrent Protection
Charge Pump (CP1 and CP2). The charge pump is used to
generate a gate supply greater than that of VBB for driving the
source-side FET 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 FET gates.
Capacitor values should be Class 2 dielectric ±15% maximum,
or tolerance R, according to EIA (Electronic Industries Alliance)
specifications.
VREG (VREG). This internally-generated voltage is used to oper-
ate the sink-side FET 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 condition, the FET outputs of the
A4987 are disabled.
Capacitor values should be Class 2 dielectric ±15% maximum,
or tolerance R, according to EIA (Electronic Industries Alliance)
specifications.
Shutdown. In the event of a fault, overtemperature (excess TJ)
or an undervoltage (on VCP), the FET outputs of the A4987 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.
Sleep Mode ( ¯S¯¯L¯¯E¯¯E¯¯P¯ ). To minimize power consumption
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 A4987 into
Sleep mode. When emerging from Sleep mode, in order to allow
the charge pump to stabilize, provide a delay of 1 ms before issu-
ing a logic command.
Mixed Decay Operation. The bridge operates in Mixed
Decay mode, as shown in figures 5 through 7. As the trip point
is reached, the A4987 initially goes into a fast decay mode for
31.25% of the off-time, tOFF. After that, it switches to Slow Decay
mode for the remainder of tOFF. A timing diagram for this feature
appears in figure 4.
Synchronous Rectification. When a PWM-off cycle is
triggered by an internal fixed-off time cycle, load current recir-
culates in Mixed Decay mode. This synchronous rectification
feature turns on the appropriate FETs during current decay, and
effectively shorts out the body diodes with the low FET RDS(ON).
This reduces power dissipation significantly, and can eliminate
the need for external Schottky diodes in many applications. Syn-
chronous rectification turns off when the load current approaches
zero (0 A), preventing reversal of the load current.
5 A / div.
Fault latched
t→
Figure 1. Short-to-ground event
5 A / div.
Fixed off-time
t→
Figure 2. Shorted load (OUTxA → OUTxB) in
Slow decay mode
5 A / div.
Fixed off-time
Fast decay portion
(direction change)
t→
Figure 3. Shorted load (OUTxA → OUTxB) in Mixed decay mode
Allegro MicroSystems, Inc.
7
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
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