LMR16006: How to charge the Cboot

user6360875

Part Number: LMR16006

LMR16006 is a non-sync mode，when the buck regulator works in CCM , how to charge the Cboot cap?

-when the high-side MOS open, CBoot cap discharges,

when high-side MOS close, the inductor L1 current began to flow through the diode D1, and the SW is clamped to -0.7V ,

so if the WinFET opens to charge the Cboot, no current flows because the SW point is clamped to -0.7V ，so how to charge the Cboot cap ,pls show me

thanks

internal circuit

over 2 years ago

0 Andy Chen over 2 years ago

TI__Mastermind 27645 points

The Cboot will be charged if SW node can be pull low close to 0V.

The IC will enter Sleep mode if inductor current is too small, the IC will turn on WimpFET first to charge up Cboot, then turn-on HS FET .

B R

Andy

0 user6360875 over 2 years ago in reply to Andy Chen

Intellectual 280 points

Thanks

"The Cboot will be charged if SW node can be pull low close to 0V."

I still can not figure out this ；

check as the following waveform from the datasheet of LMR 16006

SW node

As your mean: when SW node close to 0V , then charge the Cboot , but as the above waveform ,the △t is too small ，

so how to ensure to fully charge the Cboot ? is that mean the Cboot Charging just only take little time ?

pls

thks

+1 Andy Chen over 2 years ago in reply to user6360875

TI__Mastermind 27645 points

When SW node close to 0V, then inside refresh switch between VIN and BOOT pin will turn on as long as the Cboot voltage reach 5V, the charging time is quite shot because of small Cboot and switch ON resistor.

B R

Andy

0 user6360875 over 2 years ago in reply to Andy Chen

Intellectual 280 points

thanks i got that

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LMR16006: How to charge the Cboot