APW7134 Просмотр технического описания (PDF) - Kingbright
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APW7134 Datasheet PDF : 16 Pages
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APW7134
Typical Operating Characteristics (Cont.)
PMOSFET Leakage vs Temperature
300
250
200
150
VIN=5.5V
100
50
0
-50 -25 0
25 50 75 100 125
Temperature (o C)
NMOSFET Leakage vs Temperature
800
750
700
650
VIN=5.5V
600
550
500
-50 -25 0 25 50 75 100 125
Temperature (o C)
Functional Descriptions
Main Control Loop
Pulse Skipping Mode Operation
The APW7134 has dual independent constant fre-
quency current mode PWM step-down converters. All
the main and synchronous switches are internal to
reduce the external components. During normal
operation, the internal PMOSFET is turned on, but is
turned off when the inductor current at the input of
ICOMP to reset the RS latch. The load current increases,
it causes a slight decrease in the feedback voltage,
which in turn, causes the EA’s output voltage to in-
crease until the average inductor current matches the
new load current. While the internal power PMOSFET
is off, the internal power NMOSFET is turned on until
the inductor current starts to reverse, as indicated by
the current reversal comparator IRCMP, or the begin-
ning of next cycle. When the NMOSFET is turned off
by IRCMP, it operates in the discontinuous conduction
mode.
At light load with a relative small inductance, the
inductor current may reach zero. The internal power
NMOSFET is turned off by the current reversal
comparator, IRCMP, and the switching voltage will ring.
This is discontinuous mode operation, and is normal
behavior for the switching regulator. At very light load,
the APW7134 will automatically skip some pulses in
the pulse skipping mode to maintain the output
regulation. The skipping process modulates smoothly
depend on the load.
Short Circuit Protection
In the short circuit situation, the output voltage is
almost zero volts. Output current is limited by the
ICOMP to prevent the damage of electrical circuit. In the
normal operation, the two straight line of the inductor
current ripple have the same height, it means the
volts-seconds product is the same. When the short
circuit operation occurs, the output voltage down to
Copyright © ANPEC Electronics Corp.
9
Rev. A.1 - Aug., 2006
www.anpec.com.tw
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