FAN7585 Просмотр технического описания (PDF) - Fairchild Semiconductor
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FAN7585 Datasheet PDF : 16 Pages
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FAN7585
4. Remote On/Off & Delay Block
Vref
Ton
Toff
12
5V
REM
PWM
Ion
Rpull
Trem
5
A
B
C
REM 6
COMP6
1.2 5V
PG
Block
Remote On/Off
Irem
Ion+Ioff
Q1
Q2
Trem 2.2V
0.1 uF
COMP
0.6V↔1.8V
Ioff = Irem - Ion
∆Von=2V, ∆Voff=2.1V
Remote On/Off section is controlled by a microprocessor. If a high signal is supplied to the Remote On/Off input(Pin6), the
output of COMP6 becomes high status. The output signal is transferred to ON/OFF delay block and PG block.
If no signal is supplied to Pin6, Pin6 maintains high status(=5V) for pull-up resistor, Rpull.
When Remote On/Off is high, it produces PWM(Pin6) "High" signal after ON delay time (about 8ms with CTREM=0.1uF) for
stabilizing system. Then, all outputs (+3.3V, +5V, +12V) are grounded.
When Remote On/Off is changed to "Low", it produces PWM "Low" signal after Off delay time (about 24ms with
CTREM=0.1uF) for stabilizing the system. If REM is low, then PWM is low. That means the main SMPS is operational. When
REM is high, PWM is high and the main SMPS is turned off.
Remote On/Off delay time can be calculated by following equation.
Ton
=
K1
×
C-----T---R----E----M-----×-----∆----V----o----n-
Ion
≈
0.95
×
0----.-1----u----F-----×-----2----V--
23uA
=
8msec
Toff
=
K2
×
-C----T---R----E---M------×-----∆----V----o----f--f
Ioff
≈
0.8
×
0----.-1----u----F-----×-----2---.--1----V--
7uA
=
24msec
k1, k2: constant value gotten by test
In above equation, a typical capacitor value is 0.1uF. If the capacitor is changed to larger value, it can cause malfunction in
case of AC power on at "REM=High". Because PWM maintains Low status and main power turns on for on delay time. So
you should use 0.1uF or smaller capacitor.
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