SA07U Apex Microtechnology Corporation, SA07U Datasheet - Page 5

• Manufacturer Part Number: SA07U
• Description: PWM Amplifier
• Manufacturer: Apex Microtechnology Corporation

SA07
FIGURE A. CURRENT LIMIT WITH
SHUTDOWN VOLTAGE MODE.
FIGURE B. CURRENT LIMIT WITH
SHUTDOWN CURRENT MODE.
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SENSE pins. The noise spikes could trip the current limit
threshold which is only 100 mV. R
adjusted so as to reduce the switching noise well below 100
mV to prevent false current limiting. The sum of the DC level
plus the noise peak will determine the current limiting value. As
in most switching circuits it may be difficult to determine the
true noise amplitude without careful attention to grounding of
the oscilloscope probe. Use the shortest possible ground lead
for the probe and connect exactly at the GND terminal of the
amplifier. Suggested starting values are C
R
lated by:
maximum desired current. In current mode the required value
of each R
divided down by 2 (see Figure B). If R
divide down the sense voltage. The shutdown divider network
will also have an effect on the filtering circuit.
This data sheet has been carefully checked and is believed to be reliable, however, no responsibility is assumed for possible inaccuracies or omissions. All specifications are subject to change without notice.
FILTER
Switching noise spikes will invariably be found at the I
The required value of R
where R
= 5k .
R
LIMIT
LIMIT
LIMIT
I LIMIT/SHDN
I LIMIT/SHDN
I SENSE A
I SENSE B
I SENSE A
I SENSE B
= .1 V / I
is 2 times this value since the sense voltage is
is the required resistor value, and I
R
LIMIT
LIMIT
R
R
C
C
FILTER
FILTER
LIMIT
FILTER
FILTER
R
R
1K
1K
LIMIT
LIMIT
in voltage mode may be calcu-
FILTER
1K
R
SHDN
SHDN
SHUTDOWN
and C
SA07U REV. B DECEMBER 1998 © 1998 Apex Microtechnology Corp.
R
SIGNAL
is used it will further
SHDN
SHUTDOWN
FILTER
SIGNAL
FILTER
= .001uF,
should be
LIMIT
is the
SHUTDOWN
limiting circuitry. The two functions may be externally com-
bined in voltage and current modes as shown below in Figures
A and B. The R
and can be considered zero for this application. In Figure A,
R
After a suitable noise filter is designed for the current limit,
adjust the value of R
shutdown signal at the I LIMIT/SHDN pin when the shutdown
signal is high. Note that C
noise spikes and the shutdown signal. Shutdown and current
limit operate on each cycle of the internal switching rate. As
long as the shutdown signal is high the output will be disabled.
PROTECTION CIRCUITS
bridge output transistors. On each cycle should any fault
condition be detected all output transistors in the bridge are
shut off. Faults protected against are: shorts across the out-
puts, shorts to ground, and over temperature conditions.
Should any of these faults be detected, the output transistors
will be latched off.* In addition there is a built in dead time
during which all the output transistors are off. The dead time
removes the possibility of a momentary conduction path through
the upper and lower transistors of each half bridge during the
switching interval. Noise or flyback may be observed at the
outputs during this time due to the high impedance of the
outputs in the off state. This will vary with the nature of the load.
*
SHDN
To restart the SA07 remove the fault and recycle V
The shutdown circuitry makes use of the internal current
Circuits monitor the temperature and load on each of the
alternatively, toggle the I
pulse.
and 1K form a voltage divider for the shutdown signal.
LIMIT
resistors will normally be very low values
SHDN
LIMIT
FILTER
/SHDN (PIN16) with a shut down
to give a minimum 110 mV of
will filter both the current limit
CONSIDERATIONS
CC
OPERATING
or,