LM5177: how to charge the upper MOS bootstrap capacitor

Brian Li

Genius 13850 points

Part Number: LM5177

Hi team,

My customer is using our LM5177.

And they find no matter LM5177 is in BUCK mode or BOOST mode, the upper MOS is always on.

So could you please help check with this MOS always on, how to charge the upper MOS bootstrap capacitor?

Thanks,

Brian

over 1 year ago

0 Brigitte over 1 year ago

TI__Guru 65470 points

Hello Brian,

Which of the 2 upper MOS are you talking about? Do you mean in Buck mode, the boost high-side MOS is always on and in Boost mode, the buck high-side FET is always on?

If this is the case, the bootstrap caps share charge.

Best regards,
Brigitte

0 Brian Li over 1 year ago in reply to Brigitte

TI__Genius 13850 points

Hi Brigitte,

Brigitte said:
Do you mean in Buck mode, the boost high-side MOS is always on and in Boost mode, the buck high-side FET is always on?

Yes, this is the case.

Brigitte said:
If this is the case, the bootstrap caps share charge.

Could you please explain more detail for how to achieve this share?

Thanks,

Brian

0 Feng Ji over 1 year ago in reply to Brian Li

TI__Mastermind 22800 points

Hi Brian,

You can find the description in the datasheet 8.3.14 Gate Driver.

The idea is to build a charging path from HB1 to HB2 in buck mode, and from HB2 to HB1 in boost mode.

Best Regards,

Feng Ji

Power management

Power management forum

LM5177: how to charge the upper MOS bootstrap capacitor