BQ25756: 10-Cell Bidirectional DCDC Charger design

GIEDI WANG

Prodigy 20 points

Part Number: BQ25756
Other Parts Discussed in Thread: EV2400,

10-Cell Bidirectional DCDC Charger design

Input / output : 9V/ 3A 27W

Battery 10-Cells: 42V

1.Please help confirm whether there are any modification suggestions in the circuit diagram

2.Battery discharge to 9V 3A, the output voltage is only 8.2V at 3A load. What are the countermeasures and suggestions?

3.When the VAC device is removed, the VAC voltage is still 9V. Is it possible to design the VAC voltage to drop to 0V after the VAC device is removed?

9 months ago

0 Utsav Gupta 9 months ago

TI__Intellectual 2630 points

For schematic review please see link below. It is our schematic and layout checklist.

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1277772/faq-bq25756-schematic-and-layout-checklist

Please elaborate what is the issue for the second point. Could you explain the full situation. It is not clear.

When VAC supply is removed, the VAC should definitely be 0. Maybe there is some error in your circuit which can be rectified by checking using above link.

0 GIEDI WANG 9 months ago in reply to Utsav Gupta

Prodigy 20 points

2.Battery discharge to Vac, the output voltage drops from 9V/0A to 8.2V/3A. What countermeasures and suggestions are there to stabilize the voltage at 9V?

3. When the VAC device is removed, the VAC voltage does not drop directly to 0V, but slowly drops from 9V to 0V (as shown in the picture). Is there a problem with the circuit?

0 Utsav Gupta 9 months ago in reply to GIEDI WANG

TI__Intellectual 2630 points

2. I have never seen this before. Either there is a problem with your ACUV or VAC_DPM or there is a short somewhere in your circuit and the setup is not correct.

3. There is no problem with the device. It seems that you have a capacitor connected with your supply or the supply has an internal cap which prevents it from rising and falling instantaneously.

0 GIEDI WANG 8 months ago in reply to Utsav Gupta

Prodigy 20 points

We use BQ25756EVM+EV2400 confirm the AC_OUT voltage curve .(Attached AC_OUT voltage.pdf)

The AC_OUT voltage does not drop directly to 0V, but slowly drops from 9V to 0V. Is there a problem with the circuit?AC_OUT voltage.pdf

0 Utsav Gupta 8 months ago in reply to GIEDI WANG

TI__Intellectual 2630 points

Some questions about your AC_OUT PDF.

1. Why EN_CHG = 0 ? It should be 1 if you want to enable and use the charger.

2. Why ICHG 4A when IOUT 3A desired ?

3. Do you want to use the charger in reverse mode ? The reason when VAC device is removed, VAC still 9V is because you are in reverse mode with reverse voltage set at 9V.

4. The reason voltage slowly goes to zero after reverse mode and charging disabled and not immediately may be because of the supply. It may have capacitor connected to it. Please remove cap or try different supply.

5.Battery discharge to 9V due to reverse mode operation.

Schematic looks okay.

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BQ25756: 10-Cell Bidirectional DCDC Charger design