The clock frequency is internally set to a frequency of ap-
proximately 45kHz. The CLK OUT pin will normally be tied
to the CLK IN pin. The clock is divided by two and applied to
an RC network which produces a ramp signal at the –PWM/
RAMP pin. An external clock signal can be applied to the CLK
IN pin for synchronization purposes. If a clock frequency lower
than 45kHz is chosen an external capacitor must be tied to the
–PWM/RAMP pin. This capacitor, which parallels an internal
capacitor, must be selected so that the ramp oscillates 4 volts
p-p with the lower peak 3 volts above ground.
PWM INPUTS
The full bridge driver may be accessed via the pwm input
comparator. When +PWM > -PWM then A OUT > B OUT. A
motion control processor which generates the pwm signal can
drive these pins with signals referenced to GND.
PROTECTION CIRCUITS
In addition to the externally programmable current limit there
is also a fixed internal current limit which senses only the high
side current. It is nominally set to 140% of the continuous
rated output current. Should either of the outputs be shorted
to ground the high side current limit will latch off the output
transistors. Also, the temperature of the output transistors is
continually monitored. Should a fault condition occur which
raises the temperature of the output transistors to 165°C the
thermal protection circuit will activate and also latch off the
output transistors. In either case, it will be necessary to remove
the fault condition and recycle power to V
CC
to restart the circuit.
noise spikes could trip the cur-
rent limit threshold which is only
100 mV. R
FILTER
and C
FILTER
should
R
LIMIT
be adjusted so as to reduce the
I SENSE B
switching noise well below 100
1K
mV to prevent false current limit-
ing. The sum of the DC level plus
R
LIMIT
the noise peak will determine
the current limit-
SHUTDOWN
I LIMIT/SHDN
R
ing value. As in
SIGNAL
FILTER
most switching
R
SHDN
C
FILTER
circuits it may
be difficult to de-
FIGURE B. CURRENT LIMIT WITH
termine the true
SHUTDOWN CURRENT MODE.
noise amplitude
without careful attention to grounding of the oscilloscope probe.
Use the shortest possible ground lead for the probe and con-
nect exactly at the GND terminal of the amplifier. Suggested
starting values are C
FILTER
= .01uF, R
FILTER
= 5k .
The required value of R
LIMIT
in voltage mode may be cal-
culated by:
R
LIMIT
= .1 V / I
LIMIT
where R
LIMIT
is the required resistor value, and I
LIMIT
is the
maximum desired current. In current mode the required value
of each R
LIMIT
is 2 times this value since the sense voltage is
divided down by 2 (see Figure B). If R
SHDN
is used it will further
divide down the sense voltage. The shutdown divider network
will also have an effect on the filtering circuit.
I SENSE A
1K
BYPASSING
Adequate bypassing of the power supplies is required for
proper operation. Failure to do so can cause erratic and low
efficiency operation as well as excessive ringing at the out-
puts. The Vs supply should be bypassed with at least a 1µF
ceramic capacitor in parallel with another low ESR capacitor
of at least 10µF per amp of output current. Capacitor types
rated for switching applications are the only types that should
be considered. The bypass capacitors must be physically
connected directly to the power supply pins. Even one inch of
lead length will cause excessive ringing at the outputs. This
is due to the very fast switching times and the inductance of
the lead connection. The bypassing requirements of the Vcc
supply are less stringent, but still necessary. A .1µF to .47µF
ceramic capacitor connected directly to the Vcc pin will suffice.
CURRENT LIMIT
There are two load current sensing pins, I SENSE A and I
SENSE B. The two pins can be shorted in the voltage mode
connection but both must be used in the current mode connec-
tion (see figures A and B). It is recommended that R
LIMIT
resistors
be non-inductive. Load current flows in the I SENSE pins. To
avoid errors due to lead lengths connect the I LIMIT/SHDN pin
directly to the R
LIMIT
resistors (through
I SENSE A
the filter network
and shutdown di-
R
LIMIT
vider resistor) and
I SENSE B
connect the R
LIMIT
1K SHUTDOWN
resistors directly to
I LIMIT/SHDN
R
SIGNAL
FILTER
the GND pin.
Switching noise
R
SHDN
C
FILTER
spikes will invariably
be found at the I
FIGURE A. CURRENT LIMIT WITH
SENSE pins. The
SHUTDOWN VOLTAGE MODE.
STARTUP CONDITIONS
The high side of the all N channel output bridge circuit is
driven by bootstrap circuit and charge pump arrangement. In
order for the circuit to produce a 100% duty cycle indefinitely
the low side of each half bridge circuit must have previously
been in the ON condition. This means, in turn, that if the input
signal to the SA03 at startup is demanding a 100% duty cycle,
the output may not follow the command and may be in a tri-
state condition. The ramp signal must cross the input signal
at some point to correctly determine the output state. After the
ramp crosses the input signal level one time, the output state
will be correct thereafter.
4
SA03U
P r o d u c t I n n o v a t i o nF r o m
SA03
ContACting CiRRUS LogiC SUPPoRt
For all Apex Precision Power product questions and inquiries, call toll free 800-546-2739 in North America.
For inquiries via email, please contact apex.support@cirrus.com.
International customers can also request support by contacting their local Cirrus Logic Sales Representative.
To find the one nearest to you, go to www.cirrus.com
IMPORTANT NOTICE
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to change without notice and is provided "AS IS" without warranty of any kind (express or implied). Customers are advised to obtain the latest version of relevant
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does not extend to other copying such as copying for general distribution, advertising or promotional purposes, or for creating any work for resale.
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SUITABLE FOR USE IN PRODUCTS SURGICALLY IMPLANTED INTO THE BODY, AUTOMOTIVE SAFETY OR SECURITY DEVICES, LIFE SUPPORT PROD-
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CUSTOMER OR CUSTOMER’S CUSTOMER USES OR PERMITS THE USE OF CIRRUS PRODUCTS IN CRITICAL APPLICATIONS, CUSTOMER AGREES,
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