SMP402SC Просмотр технического описания (PDF) - Power Integrations, Inc
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SMP402SC Datasheet PDF : 16 Pages
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Functional Description (cont.)
POLARITY current threshold.
Regulation of the output voltage is
detected by a comparator which looks
for error amplifier saturation in the output
high (maximum duty cycle) state.
Power supply turn on and turn off with a
slowly changing input voltage is shown
in Figure 4 as measured using the circuit
shown in Figure 6. Also shown are the
level and polarity outputs. The input
voltage must rise above 32 V before the
SMP402 will turn on. At this input
voltage the current through R1 into the
SENSE+ input exceeds the threshold
current (typically 23 µA), the LEVEL
and POLARITY outputs go high, and
the power supply turns on. As the input
voltage goes down, LEVEL will go low
at approximately 30 V, but POLARITY
will stay high. As the input voltage
continues to drop, POLARITY goes low
at approximately 12 V and the converter
loses regulation at approximately 10 V
and turns off. The LEVEL output will
go high and the power supply turns on
when the input voltage reaches -32 V.
POLARITY stays low to indicate that
the input voltage has reversed polarity.
As the negative input voltage falls toward
zero, LEVEL goes low at approximately
-30 V and the converter loses regulation
and turns off at approximately -10 V.
SMP402
Enable
The power supply can be shut down by
pulling the ENABLE pin low. It is
internally pulled up to VS with a 100 µA
(nominal) current source. However, it is
recommended that this pin be tied to V
S
if it is unused.
P-Channel Output Transistor
The output MOSFET is a 90 V pass
transistor capable of supplying >200
mA. To minimize switching noise and
EMI, it is important to keep the path
from OUT through the output diode, the
input storage capacitor, and into V as
IN
short as possible.
INPUT VOLTAGE CONDITION
Negative voltage, level too low
Negative voltage, correct level
Positive voltage, level too low
Positive voltage, correct level
POLARITY
0
0
1
1
LEVEL
0
1
0
1
Figure 5. LEVEL/POLARITY Truth Table. The LEVEL and POLARITY signals are only valid when the output voltage is in regulation.
5 D
1/96
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