A3953SLB Allegro Microsystems Inc, A3953SLB Datasheet - Page 7

• Manufacturer Part Number: A3953SLB
• Description: IC MOTOR DRIVER PWM FULL 16-SOIC
• Manufacturer: Allegro Microsystems Inc

Specifications of A3953SLB

• Applications: PWM Motor Driver
• Number Of Outputs: 1
• Current - Output: ±1.3A
• Voltage - Load: 3 V ~ 50 V
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -20°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (0.300", 7.5mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

A3953
FUNCTIONAL DESCRIPTION
Internal PWM Current Control During Forward
and Reverse Operation.
off-time pulse width modulated (PWM) current-control circuit
that can be used to limit the load current to a desired value. The
peak value of the current limiting (I
of an external current sensing resistor (R
voltage (V
across the external sense resistor to the voltage on the reference
input terminal (REF) resulting in a transconductance function
approximated by:
where I
In forward or reverse mode the current-control circuitry limits
the load current as follows: when the load current reaches I
the comparator resets a latch that turns off the selected source
driver or selected sink and source driver pair depending on
whether the device is operating in slow or fast current-decay
mode, respectively.
In slow current-decay mode, the selected source driver is
disabled; the load inductance causes the current to recirculate
through the sink driver and ground clamp diode. In fast current-
decay mode, the selected sink and source driver pair are
disabled; the load inductance causes the current to flow from
ground to the load supply via the ground clamp and flyback
diodes.
SO
is the offset due to base drive current.
REF
Figure 1 — Load-Current Paths
). The internal circuitry compares the voltage
I
TRIP
R S
≈
V
BB
V
R
REF
Dwg. EP-006-13A
S
The A3953 contains a fixed
DRIVE CURRENT
RECIRCULATION (SLOW-DECAY MODE)
RECIRCULATION (FAST-DECAY MODE)
TRIP
– I
) is set by the selection
SO
S
) and reference input
TRIP
,
The user selects an external resistor (R
determine the time period (t
drivers remain disabled (see RC Fixed Off-Time section, below).
At the end of the RC interval, the drivers are enabled allowing
the load current to increase again. The PWM cycle repeats,
maintaining the peak load current at the desired value (figure 2).
INTERNAL PWM CURRENT CONTROL
DURING BRAKE-MODE OPERATION
Brake Operation - MODE Input High.
turns off both source drivers and turns on both sink drivers. For
dc motor applications, this has the effect of shorting the motor
back-EMF voltage resulting in current flow that dynamically
brakes the motor. If the back-EMF voltage is large, and there
is no PWM current limiting, the load current can increase to a
value that approaches that of a locked rotor condition. To limit
the current, when the I
disables the conducting sink drivers. The energy stored in the
motor inductance is discharged into the load supply causing the
motor current to decay.
As in the case of forward/reverse operation, the drivers are
enabled after a time given by t
Off-Time section, below). Depending on the back-EMF voltage
(proportional to the motor decreasing speed), the load current
again may increase to I
limiting the peak load current to the desired value.
Full-Bridge PWM Motor Driver
CURRENT
ENABLE
MODE
LOAD
Fast and Slow Current-Decay Waveforms
I
TRIP
TRIP
TRIP
. If so, the PWM cycle will repeat,
RC
level is reached, the PWM circuit
Figure 2
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
OFF
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
OFF
= R
= R
T
x C
T
T
) and capacitor (C
x C
T
) during which the
T
(see RC Fixed
RC
The brake circuit
Dwg. WP-015-1
T
) to
6