點晶科技股份有限公司
SILICON TOUCH TECHNOLOGY INC.
PS121
Note1: Once AC power is turned on, Vpgi will be pulled high before +5V input. At this time,
diode D1 will be turn off. The PG delay time is dependent on Cd as follows,
⎛
⎞
Cd ×Vthcd Cd ×1.85
⎜
⎟
⎟
Td −ON = 0.216 × Cd ( pF)μ sec, T =
=
⎜
⎝
Id −ON
8.7μ
⎠
Note2: Diode D1 is connected to Vpgi to control the PG delay time when AC is off. The AC
off delay time can be controlled as follows,
Cd ×Vthcd Cd ×Vthcd
Cd ×Vthcd
× (VCd +Vthcd
R1
Cd ×1.85
× (VCd +1.85)
R1
Td −OFF
≒
=
=
=
1
2
1
2
I2 − Id
Id −OFF
)
1
Among Td−OFF equation, the × (VCd +Vthcd ) is discharged average current.
2
Note3: Since the maximum threshold voltage at Pin 3(Cd) is 1.95V, the voltage across R1
has to be higher than 2V at normal operation.
Note4: In PCB layout condition, when the input-pin(VDD) smaller than detecting threshold
voltage(Vth), the power good signal of PS121 will connect to LOW, so the
ground-pin(VSS) must connect to the most clean ground of the power supply
system to avoid noise appear.
Note5: Suggested using RC filter circuit (Rx and Cx) to decrease ripples.
Note6: Suggested using component X1 and R1 to cut down Vpgi voltage.
Note7: Suggested using component X2 to avoid overshoot voltage damages IC.
Voltage Detecting IC
-5-
Version：A.017
SITI [ SILICON TOUCH TECHNOLOGY INC. ]
