FPF2146 데이터 시트보기 (PDF) - Fairchild Semiconductor
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FPF2146 Datasheet PDF : 13 Pages
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Application Notes
Startup Power Sequence
VIN1 FPF2140/2/ VOUT1
3/4/6/7
VIN1
PGOOD
FLAGB
OFF ON
ON
GND
100KΩ
To Load
VIN2 FPF2140/2/ VOUT2
3/4/6/7
VIN2
PGOOD
FLAGB
ON
GND
100KΩ
TP
To Load
Power good function in sequential startup. No battery is loaded to the output
Power Good
FPF214X family has a "Power Good" feature. PGOOD pin is an
open-drain MOSFET which asserts high when the output
voltage reaches 90% of the input voltage.
PGOOD pin requires an external pull up resistor that is
connected to the output voltage when there is no battery in the
load side and the logic level of the subsequent controller
permits. This would give logic levels similar to a CMOS output
stage for PGOOD, while still keeping the option to tie the pull-up
to a different supply voltage. A typical value of 100KΩ is
recommended to be used as pull up resistor. The PGOOD pin
status is independent of the ON pin position. This mean that
PGOOD pin stays low when the load switch is OFF. If the Power
Good feature is not used in the application the pin can be
connected directly to GND.
Sequential Startup using Power Good
The power good pin can be connected to another load switch's
enable pin to implement sequential startup. PGOOD pin asserts
low when the load switch is OFF. This feature allows driving a
subsequent circuit. The above diagram illustrates power good
function in sequential startup. As the VOUT1 of the first load
switch starts to ramp to the 90% of its input voltage the second
switch remains in OFF state. Whereas the VOUT1 passes the
90% threshold, power good signal becomes active and asserts
high. This signal will turn on the second load switch and VOUT2
will start to increase. The total startup time may vary according
to the difference between supply voltages that are used in the
application.
11
FPF2140/42/43/44/46/47 Rev. D
www.fairchildsemi.com
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