BQ25756EVM: Discharge function doesn't work

Gamini Dharmasena

Part Number: BQ25756EVM
Other Parts Discussed in Thread: BQSTUDIO, BQ25756

Tool/software:

Hi,

I am trying to use BQ25756EVM to test charge/discharge functions using a 13S Li-Ion cell stack. I have connected the source power (55VDC) to J2, the Battery to J3, and the load (V regulated) to J1. I can enable charging, but cannot get the reverse mode (discharge) running. The status says the Reverse Mode Off no matter what bit settings I have. I have disabled EN_CHG and enabled EN_REV. What am I missing here to start discharging? The following is the status. Any help is greatly appreciated.

Thanks

Gamini

3 months ago

0 Ethan Galloway 3 months ago

TI__Mastermind 31225 points

Hello Gamini,

What's the input and output voltage on the charger?

Can you get reverse mode working if you only have the battery connected?

Best Regards,
Ethan Galloway

0 Gamini Dharmasena 3 months ago in reply to Ethan Galloway

Prodigy 50 points

Hi Ethan,

Reverse mode doesn't work even if only the battery (J3) and load (J1) in the system (nothing on J2). If I connect the power source to J2 then the load gets direct power from the power source on J2, and this is correct according to the schematics as they are directly connected. However, It looks like I can connect the battery to the load without external power (on J2) by installing Q5, Q6, Q7 and Q8 and driving the signals ACDRV, HDRV1, BAT_DRV and BAT_SRC selectively. Am I correct? Currently following are the warning flags and hopefully, you can get the idea of what is going on now.

0 Gamini Dharmasena 3 months ago in reply to Gamini Dharmasena

Prodigy 50 points

Hi Ethan,

I made progress!! Figured out both charging and discharging now working correctly. My settings were wrong. Is there a document that explains each of these settings in the BQStudio interface?

Thanks

Gamini

0 Ethan Galloway 3 months ago in reply to Gamini Dharmasena

TI__Mastermind 31225 points

Hello Gamini,

Great! We have a general FAQ for the BQ25756 here: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1357460/faq-bq2575x-faq-page

We also have a FAQ for reverse mode here: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1357458/faq-bq25756-what-do-i-need-to-know-about-reverse-mode-or-source-mode-for-the-bq2575x-family-of-parts

Let me know if you have any questions about this.

Best Regards,
Ethan Galloway

0 Gamini Dharmasena 3 months ago in reply to Ethan Galloway

Prodigy 50 points

Hi Ethan,

Many thanks for that useful information.

Gamini

0 Gamini Dharmasena 3 months ago in reply to Gamini Dharmasena

Prodigy 50 points

HI Ethan,

I need to control a fan and wondering whether I can do that with this eval board. I can see that there is access ot to bring in the external supply for the gates that control the buck/boost charge circuit. Is there any bit that I can drive an external relay on this board?

Many thanks

Gamini

0 Ethan Galloway 3 months ago in reply to Gamini Dharmasena

TI__Mastermind 31225 points

Hello Gamini,

I don't quite understand your question. What do you mean by external relay?

Best Regards,
Ethan Galloway

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BQ25756EVM: Discharge function doesn't work