A3964SB Allegro Microsystems Inc, A3964SB Datasheet - Page 6

• 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

A3964
Internal PWM Current Control.
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 (V
approximated by:
The reference input voltage is typically set with a resistor divider
from V
reference, the resistor divider should have an impedance of 3 kΩ
to 15 kΩ (R
minimize the effect of the REF IN input offset current.
The current-control circuitry limits the load current as follows:
when the load current reaches I
that turns off the selected source driver. The load inductance
causes the current to recirculate through the sink driver and
fl yback diode.
For each bridge, the user selects an external resistor (R
capacitor (C
which the source driver remains disabled (see the RC Fixed
Off-time section, below). The range of recommended values
for C
respectively. For optimal load current regulation, C
set to 1000 pF (see the Load Current Regulation section, 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.
the PWM control circuit, the C
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 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.
During internal PWM operation, at the end of the t
comparator’s output is blanked and C
from approximately 1.1 volts by an internal current source of
approximately 1 mA. The comparator output remains blanked
T
and R
REF(OUT)
REF(IN)
D
T
T
) to determine the time period (t
= R
are 1000 pF to 1500 pF and 15 kΩ to 100 kΩ
In addition to determining the fi xed off-time of
. To ensure proper operation of the voltage
). The internal circuitry compares the voltage
REF(IN)
A
+R
B
). Within this range, a low impedance will
) resulting in a transconductance function
I
TRIP
≈
T
TRIP
component sets the comparator
The A3964 contain a fi xed
, the comparator resets a latch
V
TRIP
REF(IN)
T
R
begins to be charged
) is set by the selection
S
S
) and reference input
OFF
FUNCTIONAL DESCRIPTION
= R
OFF
T
T
is normally
C
time, the
T
T
) and
Dual Full-Bridge PWM Motor Driver
) during
until the voltage on C
When a transition of the PHASE input occurs, C
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
charged by an internal current source of approximately 1 mA.
The comparator output remains blanked until the voltage on C
reaches approximately 3 volts.
When the device is disabled, via the ENABLE input, C
discharged to near ground. When the device is re-enabled, C
charged by an internal current source of approximately 1 mA.
The comparator output remains blanked until the voltage on C
reaches approximately 3 volts.
The minimum recommended value for C
value ensures that the blanking time is suffi cient to avoid false
trips of the comparator under normal operating conditions. For
optimal regulation of the load current, the above value for C
is recommended and the value of R
t
below.
Load Current Regulation.
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
each time the PWM latch is 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:
I
where t
V
the electrical characteristics table. When the motor is rotating,
the back EMF generated will infl uence the above relationship.
For brush dc motor applications, the current regulation is
improved. For stepper motor applications when the motor is
rotating, the effect is dependent on the polarity and magnitude of
the motor’s back EMF.
OFF
AVG
BB
OFF
. For more information regarding load current regulation, see
≈
is the motor supply voltage and t
[(V
and the minimum on-time pulse t
OFF
BB
– V
= R
SAT(SOURCE+SINK)
T
C
T
, R
1.05 (t
LOAD
T
reaches approximately 3 volts.
) x t
ON(min)
is the series resistance of the load,
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
Because the device operates in a
ON(min)
max + t
max] – [1.05 (V
T
can be sized to determine
OFF
ON(min)
ON(min)
) x R
T
is 1000 pF. This
max is specifi ed in
LOAD
SAT(SINK)
max that occurs
T
is discharged
+ V
T
T
is
F
) x t
is
T
T
OFF
is
T
T
]
5