BQ25750: Reverse mode operation and current limit

Ben

Part Number: BQ25750

Tool/software:

HI,

What i understand the reverse mode of BQ25750, is operating buck-boost path reversely without VAC and only connected battery.

Also BQ25750 monitor and regulates the battery discharging current and it can control by register setting.

Q1) If the battery discharging current touch the limit, does it stop to buck-boost switching immediately?

Q2) At this time Q1, How does it operate BATFET ? because reverse mode turns off BATFET already, but the system still needs to source power.

Q3) Generally, I expect to battery discharging current(System load) is more higher than buck-boost converting output load. IBAT_REV register can be setted 20A, How can I control(design) if system load is more higher?

Thanks.

over 1 year ago

0 Ethan Galloway over 1 year ago

TI__Mastermind 31305 points

Hello Ben,

1. When the battery discharge current rises above the IBAT_REV register setting, the charger reduces the reverse mode power flow to limit the discharge current

2. Reverse mode is still ON. The BATFET would still be OFF.

3. What's voltage and current required for the system load? Can you take a guess at the peak load and how long that will last?

Best Regards,
Ethan Galloway

0 Ben over 1 year ago in reply to Ethan Galloway

Intellectual 400 points

For your information, My system battery has 1pack-14Cell(3.69V), System load is 48V@15A typically and 20~30Apeak under 10sec.

Additionally, Does it correct understand reverse mode?

- If the battery voltage is 44V after discharging, Reverse mode is still regulate 48V using buck-boost? (the System load 15A)

- how can I set to reverse mode voltage in HW default?

Pleeas explain how to operate reversmode and changing to BATFET on from reverse mode stop smoothly.

Thanks.

+1 Ethan Galloway over 1 year ago in reply to Ben

TI__Mastermind 31305 points

Hello Ben,

Ben said:
Additionally, Does it correct understand reverse mode?

- If the battery voltage is 44V after discharging, Reverse mode is still regulate 48V using buck-boost? (the System load 15A)

I'm not sure what you mean by this question. Can you rephrase this question?

Ben said:
how can I set to reverse mode voltage in HW default?

This is not possible, you'll need an MCU to do this.

We've recently wrote an FAQ on the BQ25750 power path switchover. This may help you out: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1391181/faq-bq25750-what-do-i-need-to-know-about-the-bq25750-power-path-switchover

To go above 20A in battery discharge current, you could also connect the BATFETs from the system load to SRN side of the sense resistor. This will bypass the sense resistor and remove the 20A protection. Keep in mind, you will need extremely durable FETs to survive the power path switchover.

Best Regards,
Ethan Galloway

0 Ben over 1 year ago in reply to Ethan Galloway

Intellectual 400 points

Thanks, I will check link FAQ.

Power management

Power management forum

BQ25750: Reverse mode operation and current limit