BQ24157: BQ24157: BQ24157 VBUS still have 4.2V sometimes after unplugging 5V USB or AC adapter

Hi,

Can you please share the rest of your register settings? And if possible your device schematics as well?

Best Regards,

Juan Ospina

Hi Juan Ospina,

Thank you for your reply. The register settings and circuit diagram are shown below. The blue lines indicate the parts that are different from the reference circuit.
Best Regards,

Hello Carrot,

We are looking into this and will get back to you by the end of the day.

Sincerely,

Wyatt Keller

Hi,

The 4.2V input voltage does seem to indicate that it is related to input voltage based DPM, though it is a bit unexpected that the voltage stays high. This seems to indicate that some leakage current is still going into VBUS. At 4.2V I would expect about 15 uA of leakage current going into the device which would quickly discharge the VBUS capacitors. is there any other components or devices connected to the VBUS node?  What is your battery voltage at this time?

Additionally, can you read back the register values in this state? I'd like to check what the different status bits are throughout the device.

Best Regards,

Juan Ospina

Hi, Juan Ospina

Vbus has an normally-on MOSFET switch and a voltage sense resistor connected to it.
The battery voltage is between 3.72 and 3.78V when 4.2V is output.
The register 05h indicated DPM.

REGISTER 00h 01h 02h 04h 05h
-----------------------------------------------
Charging D0 58 6C 0B 00
Vbus=4.2V D0 58 6C 0B 10
no connect 40 5E 6C 0B 00
Initial settings C0 58 6C 23 00

Sincerely,

Carrot

Hi Carrot,

Thanks for the reply,

I will review and reply after the holiday.

Best Regards,

Juan Ospina

Hi Carrot,

The register does seem to confirm this is DPM related. Can you share the VIN waveforms after USB removal that might capture the 4.2V stability? If possible please include this waveform alongside VCSIN, VPMID, and SW waveforms as well. Is it possible there is current leakage through the MOSFET?

As mentioned before, with the capacitances you shared it should not take much to discharge the VIN capacitors so I expect there might be some leakage current going into VIN that is about equal to the 14uA VIN quiescent current, otherwise the capacitors would discharge fairly quickly. Does applying a light load (very high resistance) cause VIN to fall below the 4.2V?

Best Regards,

Juan Ospina

Hi, Juan Ospina

I shared the waveform of Vin (Vbus).

It seems that there is repeated backflow to the AC adapter and charging to the battery.
When a 1kΩ load was connected, Vin fell below 4.2V.

Are there any specifications for hysteresis, response, or delay in V_IN_PDM?

Best Regards,

Carrot

wave1: Vin (Vbus) and VSCIN (Vbat)

wave2: Enlarged right side of wave1

wave3: Vpmid and Vsw near the start of 4.2V

Hi Carrot,

This does appear to be boost back behavior. This can sometimes take place on this device, particularly in circumstances where you are disconnecting a long adapter cable or due to a leaky BOOT capacitor. Can you try increasing the BOOT capacitor slightly to see if the behavior is improved.

Best Regards,

Juan Ospina

Hi, Juan Ospina

Increasing the BOOT capacitor to 470nF did not improve. The cable is 1m long. But the inside of the AC adapter is a black box. I will look for another solution.

Thank you.

Best Regards,

Carrot