If I do not put 100kohm RPG resister as your Fig.62 page-17 data sheet, then is the output voltage larger than designed value as formula VOUT=1.22 V{1+(R1/R2)}?

R1=80kohms R2=10kohms.
And there is not RPG on our PCB.
So the estimated output would be 10.98V. But we got the result around 12.7V. It was a little bit large value.
Our load is around 50mA. I think these setting are no problem.

Do you have a good advice for this case trouble?

Thanks kaos

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• Hi Kaos,

The PG pin is open-drain output that requires a pull-up resistor to Vin or Vout or other pull up voltage. If Power Good function is not used, the PG pin may be left open or connected to GND and it won’t affect the output voltage which is set by the voltage divider R1 and R2 using the equation you listed.

The tested output voltage value is a little higher than10.98V is due to the reference voltage variation and resistor tolerance. The reference voltage at Adj Pin ( Vadj) of the IC has a tiny variation with typical value of 1.22V and min 1.21V & Max 1.23V. A 10K ohm resistor with 10% tolerance has a  value somewhere between 9Kohm and 11Kohm. To improve the output voltage accuracy, choose resistors with lower tolerance (for example E96, 1% tolerance) for the voltage divider R1 and R2.

The Liner Regulator Design tool helps you choosing all the components and estimates the performance.

Best Regards,

Hong

• Hi Kaos,

The PG pin is open-drain output that requires a pull-up resistor to Vin or Vout or other pull up voltage. If Power Good function is not used, the PG pin may be left open or connected to GND and it won’t affect the output voltage which is set by the voltage divider R1 and R2 using the equation you listed.

The tested output voltage value is a little higher than10.98V is due to the reference voltage variation and resistor tolerance. The reference voltage at Adj Pin ( Vadj) of the IC has a tiny variation with typical value of 1.22V and min 1.21V & Max 1.23V. A 10K ohm resistor with 10% tolerance has a  value somewhere between 9Kohm and 11Kohm. To improve the output voltage accuracy, choose resistors with lower tolerance (for example E96, 1% tolerance) for the voltage divider R1 and R2.

The Liner Regulator Design tool helps you choosing all the components and estimates the performance.

Best Regards,

Hong

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