LM5156: VCC external bias

HI Stephen,

thank you for using the E2E forum.

I am not sure what you mean with disconnect. Can you explain in more details?

As you can see in the block diagram there is a diode from VCC to BIAS so if Vcc is higher the BIAS the Diode gets conducting.

Best regards,

 Stefan

Hi Stefan,

If you apply an external voltage to the VCC pin such that VCC_reg < VCC < BIAS, will there be any current draw into the BIAS pin of the device?

Regards,
Stephen

Hi Stefan,

Thanks, that's what I thought. Do you know if we have an estimate of what that BIAS leakage current would be in this case?

Regards,

Stephen

Hi Stephen,

I would calculate with a few uA, e.g. 2-5uA 

Best regards,

 Stefan

Hi Stefan,

Gotcha. Follow up question from the customer - is the internal circuitry powered by VCC or does it just power the gate driver? The block diagram doesn't explicitly say whether the amplifiers/comparators are powered by BIAS or VCC.

Thanks,

Stephen

HI Stephen,

most of the internal circuit is powered by VCC, esp. loop regulation components are powered by VCC.

Best regards,

 Stefan

Hi Stefan,

Do you know what, if anything, would be powered by BIAS?

Hi Stefan,

e.g. the VCC LDO , EN/UVLO logic

Best regards,

 Stefan

And those would only draw 2-5uA during operation if VCC is supplied externally?

HI Stephen,

main portion of the current would be due to the VCC LDO but if this current is delivered from Vcc, then there is just some small logic left.

E.g. the EN/UVLO logic which is covered by the shutdown current as well.

Best regards,

 Stefan