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TPS7A20: Output noise

Sai Loo
Expert 4370 points
Part Number: TPS7A20

Hi Team,

My customer is looking for a low noise input source for their audio op-amp and their supply voltage is 3.3V, and they also wanted to maintain the output voltage as closed to 3.3V as possible to maintain the signal swing. They only need 5 ~ 10mA current.

If we use the TPS7A2033 as a pass through (input 3.3V, output also 3.3V), will the LDO be able to improve the output noise? Data sheet stated the output noise spec is tested with Vin >= Vout + 0.3V  (consider 145mV dropout at 300mA output current). With 5 ~ 10mA output current, the voltage drop across the LDO will be < 5mV. Will setting the output voltage to 3.2V with 3.3V input be sufficient to keep the output noise to ~ 10uVrms?

Regards,

SK Loo

  • 0
    TI__Genius 13085 points

    Hey SK,

    Since you are looking at using the LDO with an output voltage set to 3.3V, the LDO will pass any variation on the input supply directly to the output. So the noise will be roughly equal to the input supply's noise (technically there will be some filtering by the input/output caps, but the LDO will not provide much filtering itself since it is in dropout).

    However if you were to use the TPS7A2032PDBVR which is set to a 3.2V output, then the noise would be substantially reduced since you correctly assessed that the drop across the LDO would only be ~5mV. In that instance the output noise would be ~10uVrms (noise doesn't change much with different Vin-Vout).