TPS25751: Design issue using with BQ25792 charger

Demian Zenkov

Part Number: TPS25751
Other Parts Discussed in Thread: BQ25792,

Tool/software:

I am using TPS25751 & BQ25792 to implement type-c charger for 4-cell battery package.

I have a 3v3 bus that is connected to external LDO on board. There is a switch circuit between VBAT & 3V3 circuit LDO. The problem is that this schematic works and charges the battery only if the 3V3 voltage was not applied before connecting charging cable (VBUS). If the 3V3 voltage was applied before VBUS (e.g. device was first powered on & then charging cable inserted) there is only 5V on VBUS rail instead of 20V when it operates correctly.

I measured LDO_3V3 voltage, when only VIN_3V3 voltage is applied, it's okay, there are 3.3V.

I assume the problem might be because BQ charger is not powered at the moment when TPS is, if only 3V3 power is provided.
Or because I connected PP5V to GND. I used that guide to implement sink only mode. But I am not sure what exactly causes the issue.

Can you please help with any advice, how to get the charger working even if it is powered after the 3V3 is applied.

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6 months ago

0 Chris Sterzik 6 months ago

TI__Guru 63481 points

Hello,

Please confirm that you are using this configuration; Negotiate High Voltage. Please note this is not valid to use with any supported battery chargers and the SafeMode is recommended when the PD controller manages the battery charger.

Please confirm that the configuration is sink only, 20v. https://dev.ti.com/gallery/view/USBPD/USBCPD_Application_Customization_Tool/ver/1.0.2/

Regards,

Chris

0 Demian Zenkov 6 months ago in reply to Chris Sterzik

Prodigy 30 points

Hi, Chris, thanks for your response.

1. Yes, I configured device to Negotiate High Voltage mode. Noted, I will try it in SafeMode and share results.

2. I do not change default configuration from MCU & didn't upload anything to EEPROM. Should I do it?

0 Chris Sterzik 6 months ago in reply to Demian Zenkov

TI__Guru 63481 points

Hello,

Yes. Please upload a configuration to the EEPROM. Let me know if you need any assistance with the configuration, but you should be able to fill out the questionnaire and the advanced tab is not required.

Regards,
Chris

0 Demian Zenkov 6 months ago in reply to Chris Sterzik

Prodigy 30 points

Can I resolve this issue without uploading a configuration to EEPROM? I put it to the schematics for debugging purposes and didn't plan to use it in production. Originally I planned to use it in Negotiate High Voltage mode, but cannot figure out why is it not working when charger is powered after TPS.

+1 Demian Zenkov 6 months ago in reply to Demian Zenkov

Prodigy 30 points

I guess the only way to use TPS with the configuration coming only from charger is to disconnect it from global 3v3 rail not to power it before the charger. I tried that way & it worked.

The only disadvantage is that MCU cannot read TPS register while charging is not enabled.

0 Chris Sterzik 6 months ago in reply to Demian Zenkov

TI__Guru 63481 points

Hello Demian,

Thank you for tying it out on your side. I think this use case is outside of the expected use cases described in the documentation, but again thanks for sharing your results.

Regards,
Chris

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TPS25751: Design issue using with BQ25792 charger