TPS7A33 : Input voltage -15V, output voltage -13V

Hi Junyoung,

The ratio R1/R2 is calculated as: R1/R2 = Vout/Vref - 1 = (-13) / (-1.175) - 1 = 10. So, you may choose, for example, R1 = 1.05M, R2 = 105k.

In general, the current from Vout to GND through the feedback path should be at least 100 times the leakage current in the FB pin to avoid accuracy problems. For TPS7A33, the FB leakage current is max 100nA, so the feedback path current should be at least 100nA * 100 = 10uA. This translates to R1 + R2 <= 1.3M. 

Best regards,

Nick

VREF=-1.175V 

Why is this voltage based(reference)?

Thank you.

Hi Junyoung,

Vref is an internally set bandgap voltage reference. The value is generally different for different parts, and for this part it is -1.175V.

Best regards,

Nick