[question] Why VSYS with boost converter and not PMID

[ApiumJacob]

What was VSYS with a boost converter chosen over using the PMID output of the BQ25895? I haven't played with the chip yet and I'm trying to figure out why this might be the case. The only reason I can come up with is that block diagram for the chip makes it look like PMID is only powered when there is power on VBUS. Where as VSYS can get power from VBUS or VBAT. However, there is contradicting verbiage (to the block diagram) in the datasheet that indicates that PMID can be power from VBAT.

"8.2.5 Boost Mode Operation from Battery The device supports boost converter operation to deliver power from the battery to other portable devices through PMID pin."

I realize that this is probably a better question for Ti but I learned of this chip through this design so I thought the designers of the board might have some insight. It appears that this design was lifted from the PMP4451 eval board which doesn't use the PMID pin of the BQ25895 as well.

Thanks in advance,

Jacob

[NerdyProjects]

VSYS is meant to be used to power the system, but is not able to provide 5V. PMID is connected to VIN, when present, so it will only be a regulated voltage when VIN is not present.

[SumantKhalate]

Hello @ApiumJacob

I'm working on a similar project using BQ25895 and I'll try to answer your question, not sure if that's the actual reason but anyways.

If you look further down in "8.2.5 Boost Mode Operation from Battery" it says

5. After 30 ms delay from boost mode enable

This 30ms will cause the power rail to dip, cause a glitch, or restart the pi. Hope this helps

[DjordjeMandic]

@SumantKhalate is there then any similar ic with all same features but without PMID/OTG mode