V7812-500-SMT-TR 查看數據表（PDF） - CUI INC
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V7812-500-SMT-TR Datasheet PDF : 8 Pages
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CUI Inc │ SERIES: V78-500-SMT │ DESCRIPTION: NON-ISOLATED SWITCHING REGULATOR
date 01/26/2016 │ page 7 of 8
SHUTDOWN CONTROL
The ON/OFF pin provides several features for adjusting and sequencing the power supply, a user has the flexibility of using the ON/OFF pin as:
1) A digital on/off control by pulling down the ON/OFF pin with an open-drain transistor.
ON/OFF
2) Line UVLO. If desired to achieve a UVLO voltage, a resistor divider from Vin to ON/OFF to GND can be used to disable the converter until
a higher input voltage is achieved. For example, it is not useful for a converter with 12V output to start up with a 12V input , as the
output cannot each regulation. To enable the converter when the input voltage reaches 14V, a 51kΩ/5kΩ voltage divider from Vin to GND
can be connected to the ON/OFF pin. Both the precision 1.25V threshold and 150mV hysteresis are multiplied by the resistor ratio,
providing a proportional 12% hysteresis for any startup threshold. So, the turn off threshold would be between 12.3V to 15.7V.
Vin
51 KΩ
C1
5 KΩ
GND
+ Vo u t
1 V78XX-500-SMT 5
10 7,9 6
100 F
470pF
3) Power supply sequencing. By connecting a small capacitor from ON/OFF to GND, the 2 A current source and 1.25V threshold can provide
a stable and predictable delay between startup of multiple power supplies. For example, a startup delay of roughly 64mS is provided using
100nF, and roughly 136mS by using 200nF.
Vin
C1
GND
1 V78XX-500-SMT 5 +Vout
10 7,9
C5
100nF
6
100 F
470pF
CH1: Von/off
CH2: Vo
Delay time: 64mS
Vin
C1
GND
+ Vo u t
1 V78XX-500-SMT 5
10 7,9
C5
200nF
6
100 F
470pF
cui.com
CH1: Von/off
CH2: Vo
Delay time: 136mS
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