APW7065 Просмотр технического описания (PDF) - Anpec Electronics
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APW7065 Datasheet PDF : 19 Pages
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APW7065
Typical Characteristics (Cont.)
LGATE Source Current vs. LGATE Voltage
6
5
VCC=12V
4
3
2
1
0
0
2
4
6
8
10
12
LGATE Voltage (V)
LGATE Sink Current vs. LGATE Voltage
3.5
3
VCC=12V
2.5
2
1.5
1
0.5
0
0
2
4
6
8
10
12
LGATE Voltage (V)
Functional Description
Power On Reset (POR)
The Power-On Reset (POR) function of APW7065
continually monitors the input supply voltage (VCC)
and the COMP pin. The supply voltage (VCC) must
exceed its rising POR threshold voltage. The POR
function initiates soft-start operation after VCC and
COMP voltages exceed their POR thresholds. For
operation with a single +12V power source, VIN and
VCC are equivalent and the +12V power source must
exceed the rising VCC threshold. The POR function
inhibits operation at disabled status (VCOMP is less
than 1.2V). With both input supplies above their POR
thresholds, the device initiates a soft-start interval.
seconds and then begin soft start. During soft-start,
an internal ramp connected to the one of the positive
inputs of the Gm amplifier rises up from 0V to 2V to
replace the reference voltage (0.8V) until the ramp
voltage reaches the reference voltage. The soft-start
interval is decided by the oscillator frequency
(300kHz). The formulation is given by:
Tdelay = t 2 − t1 = 2048/FOSC = 6.8ms
Tsoft−start = t3 − t2 = 1024/FOSC = 3.4ms
Soft-Start
Figure 2. shows more detail of the FB voltage ramp.
The APW7065 has a built-in digital soft-start to con- The FB voltage soft-start ramp is formed with many
trol the output voltage rise and limit the current surge small steps of voltage. The voltage of one step is about
during the start-up. In Figure 1, when VCC exceeds 12.5mV in FB, and the period of one step is about 16/
rising POR threshold voltage, it will delay 2048/Fosc FOSC. This method provides a controlled voltage rise
Copyright © ANPEC Electronics Corp.
10
Rev. A.1 - Feb., 2006
www.anpec.com.tw
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