BQ25895: If the VBUS input is 12V, how can we get a 5V output with this Q1 switch?

ju zhang56

Part Number: BQ25895

HI every8D,

As it said in the datasheet, the input voltage can be a wide range. BUT: If the VBUS input is 12V, how can we get a 5V output with this Q1 switch? I'm a newbie, and sorry for my stupid question.

over 5 years ago

0 Jeff F over 5 years ago

TI__Guru*** 148885 points

Hi Ju,

The OTG boost mode operation that provides 5V at PMID only works if V(VBUS)<UVLO. In other words, the IC can only charge the battery, using the input voltage at VBUS, or provide 5V at PMID using the battery as its input source, not both at the same time.

Regards,
Jeff

0 ju zhang56 over 5 years ago in reply to Jeff F

Prodigy 130 points

If VBUS>=5V(or in other words， the IC is in charging mode), PMID cannot provide any Power?

0 ju zhang56 over 5 years ago in reply to Jeff F

Prodigy 130 points

e2e.ti.com/.../power-bank-basics

In this link. the IC can charge the battery, and provide 5V at PMID at the same time.

0 Jeff F over 5 years ago in reply to ju zhang56

TI__Guru*** 148885 points

Hi Ju,

VBUS and PMID are only separated by FET Q1. Whatever voltage is applied at VBUS for charging we be seen at PMID, less IBUS*RDSonQ1. IF VBUS =5V, then PMID=VBUS-IBUS*RdsonQ1. Any current pulled from PMID will not be available to charge the battery.

Regards,
Jeff

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BQ25895: If the VBUS input is 12V, how can we get a 5V output with this Q1 switch?