A3964SB Allegro Microsystems Inc, A3964SB Datasheet - Page 5

• Manufacturer Part Number: A3964SB
• Description: IC MOTOR DRIVER PWM DUAL 24-DIP
• Manufacturer: Allegro Microsystems Inc

Specifications of A3964SB

• Applications: Stepper Motor Driver
• Number Of Outputs: 1
• Current - Output: ±800mA
• Voltage - Load: 5 V ~ 30 V
• Voltage - Supply: 4.75 V ~ 5.25 V
• Operating Temperature: -20°C ~ 85°C
• Mounting Type: Through Hole
• Package / Case: 24-DIP (0.300", 7.62mm)
• Operating Current: 85mA
• Operating Temperature Classification: Commercial
• Package Type: PDIP
• Operating Supply Voltage (min): 4.75V
• Operating Supply Voltage (max): 5.25V
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Internal PWM Current Control. The A3964SB and
A3964SLB contain a fixed 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
current-sensing resistor (R
(V
across the external sense resistor to the voltage on the
reference input terminal (V
transconductance function approximated by:
resistor divider from V
of the voltage reference, the resistor divider should have
an impedance of 3 k to 15 k (R
range, a low impedance will minimize the effect of the REF
IN input offset current.
follows: when the load current reaches I
tor resets a latch that turns off the selected source driver.
The load inductance causes the current to recirculate
through the sink driver and flyback diode.
(R
(t
disabled (see “RC Fixed Off-time” below). The range of
recommended values for C
pF and 15 k to 100 k respectively. For optimal load
current regulation, C
“Load Current Regulation” below). At the end of the RC
interval, the source driver is enabled allowing the load
current to increase again. The PWM cycle repeats,
maintaining the peak load current at the desired value.
RC Blanking. In addition to determining the fixed off-time
of the PWM control circuit, the C
comparator blanking time. This function blanks the output
of the comparator when the outputs are switched by the
internal current-control circuitry (or by the PHASE or
ENABLE inputs). The comparator output is blanked to
OFF
3964
DUAL FULL-BRIDGE
PWM MOTOR DRIVER
REF(IN)
T
) and capacitor (C
The reference input voltage is typically set with a
The current-control circuitry limits the load current as
For each bridge, the user selects an external resistor
= R
). The internal circuitry compares the voltage
T
C
FUNCTIONAL DESCRIPTION
T
) during which the source driver remains
TRIP
I
TRIP
) is set by the selection of an external
T
T
REF(OUT)
is normally set to 1000 pF (see
) to determine the time period
S
REF(IN)
T
V
) and reference input voltage
and R
REF(IN)
. To ensure proper operation
R
S
) resulting in a
T
component sets the
D
T
= R
are 1000 pF to 1500
A
TRIP
+R
B
, the compara-
I
). Within this
AVG
[(V
BB
– V
SAT(SOURCE+SINK)
prevent false over-current detections due to reverse-
recovery currents of the clamp diodes, and/or switching
transients related to distributed capacitance in the load.
time, the comparator’s output is blanked and C
be charged from approximately 1.1 volts by an internal
current source of approximately 1 mA. The comparator
output remains blanked until the voltage on C
approximately 3 volts.
is discharged to near ground during the crossover delay
time (the crossover delay time is present to prevent
simultaneous conduction of the source and sink drivers).
After the crossover delay, C
current source of approximately 1 mA. The comparator
output remains blanked until the voltage on C
approximately 3 volts.
C
re-enabled, C
approximately 1 mA. The comparator output remains
blanked until the voltage on C
3 volts.
1000 pF. This value ensures that the blanking time is
sufficient to avoid false trips of the comparator under
normal operating conditions. For optimal regulation of the
load current, the above value for C
the value of R
information regarding load current regulation, see below.
Load Current Regulation. Because the device operates
in a slow current-decay mode (2-quadrant PWM mode),
there is a limit to the lowest level that the PWM current
control circuitry can regulate load current. The limitation is
due to the minimum PWM duty cycle, which is a function of
the user-selected value of t
pulse t
reset. If the motor is not rotating, as in the case of a
stepper motor in hold/detent mode, a brush dc motor when
stalled or at startup, the worst case value of current
regulation can be approximated by:
T
is discharged to near ground. When the device is
During internal PWM operation, at the end of the t
When a transition of the PHASE input occurs, C
When the device is disabled, via the ENABLE input,
The minimum recommended value for C
ON(min)
1.05 (t
max that occurs each time the PWM latch is
) • t
T
T
ON(min)
is charged by an internal current source of
can be sized to determine t
ON(min)
max + t
max] – (1.05 (V
OFF
OFF
T
is charged by an internal
T
) • R
and the minimum on-time
reaches approximately
T
LOAD
is recommended and
SAT(SINK)
OFF
T
T
. For more
+ V
T
reaches
reaches
T
begins to
is
F
) • t
T
OFF
OFF
)