SA51 Datasheet, PDF (4/4 Pages) Cirrus Logic – H/BRIDGE MOTOR DRIVER/AMPLIFIER

OPERATING
CONSIDERATIONS
SA51
GENERAL
Please read Application Note 30 on "PWM Basics". Refer
to Application Note 1 "General Operating Considerations" for
helpful information regarding power supplies, heat sinking
and mounting. Visit www.apexmicrotech.com for design tools
that help automate pwm filter design and heat sink selection.
The "Application Notes" and "Technical Seminar" sections
contain a wealth of information on specific types of applica-
tions. Information on package outlines, heat sinks, mounting
hardware and other accessories are located in the "Packages
and Accessories" section. Evaluation Kits are available for most
Apex product models, consult the "Evaluation Kit" section for
details. For the most current version of all Apex product data
sheets, visit www.apexmicrotech.com.
PIN DESCRIPTION
VCC - is the low voltage supply for powering internal logic and
drivers for the lowside and highside MOSFETS. The supplies
for the highside drivers are derived from this voltage.
V_S - is the higher voltage H-bridge supply. The MOSFETS
obtain the output current from this supply pin. The voltage on
this pin is limited to +80V by the drive IC. The MOSFETS are
rated at 100 volts. Proper by-passing to GND with sufficient
capacitance to suppress any voltage transients, and to ensure
removing any drooping during switching, should be done as
close to the pins on the hybrid as possible.
A OUT - is the output pin for one half of the bridge. When
the PWM input is high, this output will be pulled up to Vs.
B OUT - is the output pin for the other half of the bridge. When
the PWM input is low, this output will be pulled up to Vs.
RSENSE - This is the common connection for the bottom of
the bridge. This can have a sense resistor connected to the Vs
return ground for current limit sensing, or can be connected
directly to ground. The maximum voltage on this pin is ±2 volts
with respect to GND.
GND - is the return connection for the input logic and Vcc.
PWM INPUT - is a TTL compatible input pin for providing the
PWM signal to modulate the output switches. The duty cycle
can be between 0% (DC low) and 100% (DC high).
DISABLE INPUT - is a TTL compatible input for providing
a shutdown signal to the hybrid for disabling all four switches
in the bridge regardless of the PWM input level. A digital 1
disables, a digital 0 enables.
TYPICAL SYSTEM OPERATION
Below is a diagram of a typical application of the SA51. The
design Vcc voltage is +12 volts and should have a low ESR
bypass capacitor such as a tantalum electrolytic. The PWM
and DISABLE signals are typically provided by some type of
microprocessor control. The PWM signal will be a TTL signal
with a pulse frequency required by the system, and pulse duty
cycles according to the required direction/speed. A 0% duty
cycle (continuous TTL low) will mean full voltage to the motor
in one direction. A 100% duty cycle (continuous TTL high) will
mean full voltage to the motor in the other direction. A 50%
duty cycle will hold the motor at 0 RPM.
Current sensing is done in this case by a 0.1 ohm sense
resistor to sense current from either leg of the bridge. It is
important to make the high current traces as wide as possible
to keep inductance down. The storage capacitor connected
to the +Vs and the hybrid GND should be large enough to
provide the high energy pulse without the voltage sagging
too far. The storage capacitor should be a low ESR ceramic
capacitor or large polypropylene capacitor. Mount capacitor
as close to the hybrid as possible. The connection between
GND and the +Vs return should not be carrying any motor
current. The sense resistor signal is common mode filtered as
necessary to feed the limiting circuitry for the microprocessor.
This application will allow full four quadrant torque control for
a closed loop servo system.
A snubber network is usually required, due to the inductance
in the power loop. It is important to design the snubber network
to suppress any positive spikes above +V_S and negative spikes
below -2V with respect to Pin 5 (GND) of the hybrid.
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SA51U REV. F JUNE 2002 © 2002 Apex Microtechnology Corp.