SA01U Apex Microtechnology Corporation, SA01U Datasheet - Page 4

• Manufacturer Part Number: SA01U
• Description: PWM Amplifier
• Manufacturer: Apex Microtechnology Corporation

SHUTDOWN
FIGURE 1.
SA01
GENERAL
mounting can be found in the “General Operating Consider-
ations” section of the Apex data book. For information on the
package outline, heatsinks, and mounting hardware see the
“Package Outlines” and “Accessories” section of the data book.
Also see Application Note 30 on “PWM Basics.”
CURRENT LIMIT
pin 8 (Isense). This limits load current and also limits current in
the event of a short of either output to +Vs. This circuit can trip
anytime during the conduction period and will hold the output
transistors off for the remainder of that conduction period.
connected as shown in the external connection diagram. It is
recommended that the resistor be a non-inductive type. Load
current flows in pin 8. No current flows in pin 10 (Shutdown/
filter) so no error will be introduced by the length of the
connection to pin 10. However, the voltage at pin 10 is com-
pared to GND (pin 4) and an error could be introduced if the
grounded end of R
board layout practice would be to connect R
tween pins 8 and 4.
amplitude and duration will be load dependent. The noise
spikes could trip the current limit threshold which is only 200
mV. R
switching noise well below 200 mV to prevent false current
limiting. The sum of the DC level plus the noise peak will
determine the current limiting value. Suggested starting values
are C
where R
maximum desired current.
SHUTDOWN
limiting circuitry. The two functions may be externally combined
as shown below in Figure 1. R
value resistor and can be considered zero for this application.
R
After a suitable noise filter is designed for the current limit adjust
the value of R
when the shutdown signal is high. This means pin 10 will reach
the 200 mV trip point in about one time constant with low output
current and less time as output current increases. The voltage
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.
SIGNAL
SD
Helpful information about power supplies, heatsinking and
The current limit function sets a peak limit on current flow in
For proper operation the current limit sense resistor must be
Switching noise spikes will invariably be found at pin 8. The
The required value of R
The shutdown circuitry makes use of the internal current
and R
C
FILTER
FILTER
FILTER
LIMIT
FILTER
= .01 F, R
and C
R
is the required resistor value, and I
SD
LIMIT
R
R
form a voltage divider for the shutdown signal.
SD
LIMIT
to give 317 mV of shutdown signal at pin 10
FILTER
LIMIT
= .2 V / I
FILTER
should be adjusted so as to reduce the
is not directly tied to pin 4. Good circuit
R
SHDN/FILTER
FILTER
LIMIT
= 5k.
I
LIMIT
SENSE
10
8
may be calculated by:
LIMIT
will normally be a very low
at pin 10 is referenced
to pin 4 (GND). C
will filter both the cur-
rent limit noise spikes
and the shutdown sig-
nal. Shutdown and cur-
rent limit operate on
each cycle of the inter-
nal switching rate. As
long as the shutdown
signal is high the output
will be disabled.
SA01U REV. E MARCH 1999 © 1999 Apex Microtechnology Corp.
LIMIT
directly be-
LIMIT
is the
FILTER
FIGURE 2.
PROTECTION CIRCUITS
transistors off. The first of these conditions is activation of the
high side current limit. Specifically, current in pin 7 (+V
monitored. The DC trip level is about 35A and response time
about 5us. As actual currents increase the response time
decreases. The external fault generally associated with this
condition is shorting one of the outputs to ground. However, a
load fault can also activate this high side current limit if the
current rise time is less than the response time of the filter
discussed under “Current Limit”. The second of these condi-
tions is activation of any of the four output transistor over-
temperature sensors at about 165 C. Ambient temperature, air
flow, amplifier mounting problems and all the previously men-
tioned high current faults contribute to junction temperature.
When either of these protection circuits are activated, the root
fault must be corrected and power cycled to restore normal
operation.
DEAD TIME
The dead time removes the possibility of a momentary conduc-
tion path through the upper and lower transistors of each half
bridge output during the switching interval. During the dead
time all output transistors are off. 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.
ERROR AMPLIFIER
highest loop accuracy it is best to configure the op amp as an
integrator (See Figure 2). Feedback can be adjusted with
appropriate poles and zeroes to properly compensate the
velocity loop for optimum stability.
ated internally. The non-inverting input of the op amp does not
have a common mode range which includes ground. R2 and R7
are used with the reference voltage provided at pin 5 to bias the
non-inverting input to +5 volts, which is approximately half of
the voltage supplied internally to the op amp. Similarly, R1 and
the parallel combination of R5 R6 are selected to bias the
inverting input also at +5 volts. Resistors R1 R2 must be
matched. Likewise the parallel combination of R5 R6 must be
matched with R7. The source impedances of the tach and the
signal source may affect the matching and should be consid-
ered in the design.
TO TACH
There are two conditions which will latch all the output
There is a dead time between the on and off of each output.
The internal error amplifier is an operational amplifier. For
The op amp is operated from a single supply voltage gener-
SIGNAL
C2
R5
R6
R4
REF OUT
R2
R7
+IN
–IN
5
1
2
R1
C1
.1µF
CONSIDERATIONS
R3
OPERATING
E/A OUT
3
S
) is