APW7158 Ver la hoja de datos (PDF) - Anpec Electronics
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APW7158 Datasheet PDF : 24 Pages
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APW7158
Function Description (Cont.)
Shunt Regulator (Cont.)
VCC(5.8V)
R
VCC12
VCC
APW7158
VCC12
Figure 3. Optional R for Shunt Regulator
Oscillator
The APW7158 provides the oscillator switching frequency
adjustment. Connect a resistor from FS pin to the ground;
the nominal 300kHz oscillator switching frequency is
increased according to the value of the resistor. Thus,
the adjustment range of the switching frequency is nomi-
nal 300kHz to 800kHz. Conversely, connecting a resistor
from FS pin to the VCC12 pin reduces the switching fre-
quency according to the value of the resistor. Thus, the
adjustment range of the switching frequency is 70kHz to
nominal 300kHz. (See Figure 4.).
Short-Circuit Protection
The APW7158 has a simple short-circuit protection to
monitor COMP1 pin and COMP2 pin for OUT1 and OUT2.
When output voltage has a short, the FB pin should start
to follow output since it is a resistor divider from the output.
The FB pin is the inverting input of Error-Amp. When FB
pin is lower than the Error-Amp reference, the VCOMP will
rise to increase the duty-cycle of the upper MOSFET gate
driver, and this allows output to get higher voltage. If the
short-circuit condition is long enough, the VCOMP will ex-
ceed the trip point 3.3V and the duty circle will hit the
maximum. This means that either Over-Current or Un-
der-Voltage condition is detected. If any of the VCOMP1 and
V exceed their trip points and hold over a filter time
COMP2
(1-2 clock cycles of switching frequency), all regulators
will shut down and require a POR on either of VCC or
VCC12 pin to restart.
1000
900
800
FS to
VCC12
700
600
500
400
300
FS to GND
200
100
0
0 100 200 300 400 500 600 700 800
Switching Frequency (kHz)
Figure 4. FS Resistance vs. Frequency
Copyright © ANPEC Electronics Corp.
15
Rev. A.2 - Aug., 2009
www.anpec.com.tw
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