TPS25751EVM: Sourcing from BQ25756 the 5V PDO

Forget the last part about flashing, i can keep jumpers the same way (from Vbatt), just need to connect J2 powersupply for flashing.

Hi Sebastien, 

Thank you for reaching out!

Your understanding is correct, PP3 is the high voltage power path (PPHV). 

1- Do you have PD logs or I2C logs of the observed behavior? 

2- Which USB key device are you testing with? Have you tested with other sink devices?

Best Regards, 

Aya Khedr 

Hello, yes i tried other sink devices.

I see that USB-pd is trying to communicate with BQ charger but does not get a response from charger. I see only one byte of activity on the I2C.

The Regn LDO is always low. I understand the LDO will go up if Vbat >3V and EN_REV = 1. Do i need to first configure the BQ IC (with EN_REV =1 to work with the TPS25751, i though the TPS25751 would configure the BQ charger autonomously based on USP-PD PDO dealt with USB device.

Hi Sebastien, 

You should not need to configure the battery charger's registers. The TPS25751 will enable reverse mode and other registers needed for sourcing. 

Could you please confirm that your hardware setup is identical to the figure from the user guide below? Please ensure that the ribbon cable is connected in the same orientation as the image below for I2C communication.  

Best Regards, 

Aya Khedr 

Yes Same connexions, J3 is a standard power supply instead of a battery for source only tests. Ribbon cable has brown wire on pin 1 for both ends.

Also jumpers are all by default for BQ charger same placement as for the picture. Only modifications i did on the devkit is R64 (FB resistor) i changed for 8.4V charging (2cells) i don't think it should affect source mode.

Hello Aya,

I did some more tests with the BQ devkit, is there an easy way to just have the REGN LDO to activate? Maybe my IC is having some issues. But i don't measure a short on the pin. I can't get any voltage on REGN pin. 

I tried simply powering from J1 with 15V, i see the PG led lights up but still no voltage on REGN pin.

Based on datasheet, Vac + CE pin low should lead to REGN LDO to start.

Should there be a voltage on REGN pin when powered from Vac or is there an easy way to confirm the LDO is working?

Thank you.

Hi Sebastien, 

I will loop in the battery charger expert to assist you.

Best Regards, 

Aya Khedr 

Ok thank you, i'll do some more tests and come back, my LDO is now going up when connecting both devkit togheter and using sink mode.

Here's a recap of the situation. 

I'm able to request 20V to sink using BQ charger, the charger goes up and switches.

I'm able to source from PP5V

If sourcing from PPHV 5V will appear on the Vbus and will toggle on and off. USB PD will send a I2C byte to BQ charger but charger will stay in sleep (no Vregn not even trying to switch)

Are there some particular things to do for reverse mode operation? I have 10V on the J3 batt input and jumpers in default mode.

update, seems like drv_sup being externally supplied helps getting a step closer to reverse operation, BQ charger seems to automatically go into error and stop. But regn goes up. I2C communication seems brief, like USB PD is polling but does not get answers.

Closing this thread since issue not related to TPS25751