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LM5158: Bias pin connect to Vout

Part Number: LM5158

Hi Team,

1. what would happen if I connect Bias to Vout instead of Vin?

2. what would happen if vin is lower than 5V when connecting bias to Vin?



  • Hi Fred,

    1. It is allowed and recommended if Vin can drop below 3.2V.   However, if your Vout is much higher than regular Vin, then the internal LDO's power dissipation would be higher than connecting BIAS to Vin.

    2. As long as Vin is >3.2V, it should not affect the operation.  If Vin can drop to lower, you may need to have a block diode at the BIAS pin to prevent discharging VCC through BIAS pin.  

    Hope this clarifies.



  • Hi,

    I thought Bias is the source to VCC, VCC should be the lower voltage point compare to bias.

    how could bias keep provide current if  3.2V<Vin<5V , I assume the internal  LDO will not work? 

  • Hi Fred,

    the full picture of the design is unfortunately missing (input voltage range / output voltage). So some assumptions needs to be done.

    you are right the Bias is the source for Vcc and if Bias is lower then 5V also Vcc is lower - see figure 8-4 in the Datasheet.

    Best regards,


  • Hello Fred, 

    I have not seen an update on this thread for the last 11 days.

    Maybe you could solve this issue already in the meantime, in this case it would be great to press the is solved button.

    If there is still something open, just let me know with the new details.

    Best regards,