BQ24192 - No SYS output until Battery is connected onto BAT pin (applied +12V on VBUS pin)

Please check the input current for soft start conditions. The system probably sinks too much load that the input current is constrained to 100mA.

This condition is described in the datasheet and I quote as below "The bq24190, bq24192, bq24192I provides soft-start when ramp up the system rail. When the system rail is below 2.2 V, the input current limit is forced to 100 mA. After the system rises above 2.2 V, the charger device sets the input current limit set by the lower value between register and ILIM pin."

Hi,

Thanks for the reply. The input current sinks about 140mA during power up on this board.

I tried to pull up OTG pin to 4V through a voltage divider, this should give input current limit to 500mA, but it behave the same. Then latter, I realized, because PSEL is pull down, the input current is limit to 3A for BQ24192 regardless OTG pin input.

Do you have other suggestions. Your help and support are much appreciated.

Best Regards.

Roger

Do you mean that even at SYS=2V, the system would pull 140mA power? It sounds a lot for such low voltage.

It would be helpful if an waveform is provide with I(VBUS), SYS, BAT, I(BAT).

Yes, on this (problematic) board, the input steady current is about 0.14A to 0.17A on VBUS pin (VBUS pin is 12v), but SYS output never reach to 4.0V (about 2V).

Following pictures (below left and right) show waveform for VBUS (CH1, +12V), VBUS_PIN(CH2, +12V through 0.47ohm), SYS (CH3).

Left picture is problem board (SN02),the SYS output only settle on 2V. RIght picture is a good board (SN01), SYS output can reach to 4V. The purple color is "CH1-CH2", which has division of 5V, divide by 0.47, should give current waveform, but for some reason, it seems no current change is recorded here (?).

Above picture show BAT pin through a 0.47ohm resistor, again, CH1 is 3.7V battery, CH2 is 3.7V through a 0.47ohm resistir (BAT pin),  SYS output CH3 (o.k.), battery peak current is about 740mV/0.47ohm = 1.5A. 

Your advise and help are much appreciated.

Thanks and Best regards.

Roger

Hi,

Do you have inputs or suggestions in term of waveforms?

Thanks.

Roger

Hi Roger,

Did you mean, after you swapped IC, problem board still showed Vsys=2V, but the other 3 boards are ok? If so, we will need to debug from board. There might be leakage path in the board.

if not, one experiment you can try is, turn on/off Q4 and watch SYS voltage change. Can you capture waveform of good and bad boards? Thanks.

Best Regards,

Linhong Qin

 

Hi Linhong,

Yes, on this particular board (SN02) Charger BQ24192 was swapped (not once, but twice), but SYS_VDD still show 2V. I also checked all surrounding components, I am not able to find anything wrong. Other three boards are fine.

How do I turn on/off Q4? what waveform we need compare between good and bad boards?

Your help are greatly appreciated.

Thanks and Best Regards.

Roger

Hi Roger,

Ok. So, most likely BQ24192 IC is good, something in SN02 might have triggered the problme. In this sense, Q4 is probably ok. By the way, you can set REG07[5] to turn off Q4.

When power off, can you ohm out SYS and BAT, and compare to good board.

Do you have anything connected to SYS_VDD at all? if so, can you disconnect and re-try if you still get 2V?

Do you use GUI? when power up, can you capture the screen when 2V is shown? I want to see the Register status.

Have you tried other VBUS voltages. We support 3.9v to 17V.

Thanks.

Best Regards,

Linhong