BQ25703A: BQ25703A unused pins

Nik

Part Number: BQ25703A
Other Parts Discussed in Thread: PMP40312

Hello.
I'm designing module with BQ25703A charger. I'm planning to use only I2C to communicate with it. I read datasheet, but in my case what to do with some pins is not clear to me.
According to EVM CHRG_OK, PROCHOT, CMPOUT have pull up to +3V3. But I don't have 3V3 source on board. So:
1. CHRG_OK pin. Datasheet says “connect to the pullup rail”. If I don’t use it, can I leave CHRG_OK floating? Can I still get its correct status via I2C ChargerStatusRegister, AC_STAT bit?
2. PROCHOT pin. If I don’t use it, can I leave CHRG_OK floating?
3. CMPIN and CMPOUT. I don’t use it. I grounded CMPIN. Can I leave CMPOUT floating?
4. EN_OTG pin. To have control over OTG mode via I2C can I pull this pin to VDDA (REGN)? Or it doesn’t work and I cannot control OTG without pulling this pin to +3V3 source?
5. Also CHRG_OK is active high. So if I pull it up, for example as in EVM, without connected adapter, will it constantly draw current through 10kOhm from +3V3, that powered from battery?..

Thank you!

over 4 years ago

0 Shishuo Zhao over 4 years ago

TI__Expert 3320 points

Hi Nik,

1,CHRG_OK pin please pull up to 3.3V through 10k resistor,even not in use.

2, /PROCHOT pin please pull up to 3.3V through 10k resistor,even not in use.

3,Nope, CMPOUT pin please pull up to 3.3V through 10k resistor,even not in use.

4,The Absolute maximum voltage on OTG/VAP pin is 7V, therefore we recommend to pull up this pin to 3.3V. The REGN is 6V LDO.

5,Your concern is only valid when it is not in low power mode. When Adapter is not connected, the part will go into Low power mode by default. In low power mode, the CHRG_OK pin will not be pulled low, therefore there is no loss concern.

Regards

0 Nik over 4 years ago in reply to Shishuo Zhao

Prodigy 60 points

Thank you for you answer!

But in TI reference design PMP40312 BQ25703A has CHRG_OK, PROCHOT and AMPOUT floating. Is it wrong in reference design?

http://www.ti.com/lit/df/tidruy1/tidruy1.pdf

0 Shishuo Zhao over 4 years ago in reply to Nik

TI__Expert 3320 points

Hi there,

We have a dedicated BQ2570X EVM reference design. We recommend to follow the reference design below.

Regards

0 Nik over 4 years ago in reply to Shishuo Zhao

Prodigy 60 points

Thank you for answer!

Yes, I have already studied BQ2570X EVM. I understand that it contains full schematic to provide all BQ25703A functions.

But my design is cost and space sensitive. Additional 3V3 power supply is undesirable. It still isn't clear to me why I need to pull up unused open drain outputs. What does it leads to? Will some other BQ25703A functions wouldn't work correctly?

0 Shishuo Zhao over 4 years ago in reply to Nik

TI__Expert 3320 points

Hi Nik,

Confirmed with the team, it should be ok to float CHRG_OK, PROCHOT and CMPOUT pins.

Regards

Shishuo

0 Nik over 4 years ago in reply to Shishuo Zhao

Prodigy 60 points

Thanks a lot!

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BQ25703A: BQ25703A unused pins