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# TPS74401: How to design the power supply for bias pin to get the input Voltages as Low as 0.9 V

Part Number: TPS74401

hi, how to design the power supply for bias pin to get the input Voltages as Low as 0.9 V? and How 0.9V is calculated？

• Hello Steve,

0.9V on the input is the minimum voltage that the device would need if you were trying to regulate a 0.8V output voltage.

BIAS supply is required when VIN is below VOUT + VDO (VBIAS).

0.9V is calculated by the IC designer as the minimum voltage that internal circuitry needs to remain functional.

Best,

Juliette

• Thanks, Can it be realized when suppling 3.3V to bias, input 0.95V, output 0.8V/2A？

• Hey Steve,

3,3V is above the VDO(BIAS) for that current.

Your VBIAS - VOUT = 2.5V. At that differential, your VDO(VIN) will be around 110mV.

Your VIN - VOUT = 150mV. You have sufficient headroom for this application.

Verify that the noise and PSRR are adequate for you application. Those values tend to suffer when there is a smaller headroom.

Best,

Juliette