A3953SLBTR-T Allegro Microsystems Inc, A3953SLBTR-T Datasheet - Page 10

• Manufacturer Part Number: A3953SLBTR-T
• Description: IC MOTOR DRIVER PWM FULL 16-SOIC
• Manufacturer: Allegro Microsystems Inc

Specifications of A3953SLBTR-T

• 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)
• Motor Type: Full Bridge
• No. Of Outputs: 1
• Output Current: 1.3A
• Output Voltage: 50V
• Supply Voltage Range: 3V To 5.5V
• Driver Case Style: SOIC
• No. Of Pins: 16
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 620-1133-2; A3953SLBTR-T

A3953
Thermal protection circuitry turns off all drivers should the
junction temperature reach 165°C (typical). This is intended
only to protect the device from failures due to excessive junction
temperatures and should not imply that output short circuits
are permitted. The hysteresis of the thermal shutdown circuit is
approximately 15°C.
APPLICATION NOTES
Current Sensing.
above the calculated value of I
the drivers. The amount of overshoot can be approximated by:
where V
voltage of the load, R
inductance of the load respectively, and t
the electrical characteristics table.
The reference terminal has a maximum input bias current of ±5
μA. This current should be taken into account when determining
the impedance of the external circuit that sets the reference
voltage value.
To minimize current-sensing inaccuracies caused by ground trace
I x R drops, the current-sensing resistor should have a separate
return to the ground terminal of the device. For low-value sense
resistors, the I x R drops in the printed wiring board can be
significant and should be taken into account. The use of sockets
should be avoided as their contact resistance can cause variations
in the effective value of R
Generally, larger values of R
but can result in excessive heating and power loss in the sense
resistor. The selected value of R
maximum voltage rating of 1.0 V (0.4 V for V
operation), for the SENSE terminal, to be exceeded.
The current-sensing comparator functions down to ground
allowing the device to be used in microstepping, sinusoidal, and
other varying current-profile applications.
Thermal Considerations.
recommended that the maximum junction temperature be kept
below 110°C to 125°C. The junction temperature can be measured
best by attaching a thermocouple to the power tab/batwing of the
device and measuring the tab temperature, T
temperature can then be approximated by using the formula:
where V
I
OS
BB
F
may be chosen from the electrical specification table
≈
is the motor supply voltage, V
(V
T
J
BB
≈ T
– [(I
LOAD
TAB
The actual peak load current (I
TRIP
+ (I
S
.
and L
x R
S
LOAD
reduce the aforementioned effects
TRIP
S
LOAD
LOAD
For reliable operation it is
should not cause the absolute
L
x 2 x V
due to delays in the turn off of
LOAD
) + V
are the resistance and
PWM(OFF)
BEMF
F
BEMF
x R
TAB
CC
is the back-EMF
]) x t
. The junction
JT
= 3.3 V
is specified in
)
PWM(OFF)
PEAK
) will be
for the given level of I
package thermal resistance table for the appropriate package.
The power dissipation of the batwing packages can be improved
by 20% to 30% by adding a section of printed circuit board
copper (typically 6 to 18 square centimeters) connected to the
batwing terminals of the device.
The thermal performance in applications that run at high load
currents and/or high duty cycles can be improved by adding
external diodes in parallel with the internal diodes. In internal
PWM slow-decay applications, only the two ground clamp diodes
need be added. For internal fast-decay PWM, or external PHASE
or ENABLE input PWM applications, all four external diodes
should be added for maximum junction temperature reduction.
PCB Layout.
be decoupled with an electrolytic capacitor (>47 μF is
recommended) placed as close to the device as is physically
practical. To minimize the effect of system ground I x R drops on
the logic and reference input signals, the system ground should
have a low-resistance return to the motor supply voltage. See also
the Current Sensing and Thermal Considerations sections, above.
Fixed Off-Time Selection.
switching losses will decrease, low-level load-current regulation
will improve, EMI will be reduced, the PWM frequency will
decrease, and ripple current will increase. The value of t
be chosen for optimization of these parameters. For applications
where audible noise is a concern, typical values of t
to be in the range of 15 ms to 35 ms.
Stepper Motor Applications.
can be used to optimize the performance of the device in
microstepping/sinusoidal stepper-motor drive applications. When
the load current is increasing, slow decay mode is used to limit
the switching losses in the device and iron losses in the motor.
This also improves the maximum rate at which the load current
can increase (as compared to fast decay) due to the slow rate of
decay during t
mode is used to regulate the load current to the desired level. This
prevents tailing of the current profile caused by the back-EMF
voltage of the stepper motor.
In stepper-motor applications applying a constant current to
the load, slow-decay mode PWM is typically used to limit the
switching losses in the device and iron losses in the motor.
DC Motor Applications
speed of a dc motor can be controlled by PWM of the PHASE
or ENABLE inputs, or by varying the reference input voltage
(REF). In digital systems (microprocessor controlled), PWM of
the PHASE or ENABLE input is used typically thus avoiding
Full-Bridge PWM Motor Driver
OFF
The load supply terminal, V
. When the load current is decreasing, fast-decay
LOAD
. The value for R
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
. In closed-loop systems, the
With increasing values of t
The MODE terminal
θJT
BB
is given in the
, should
OFF
are chosen
OFF
can
OFF,
9