BQ24725A: Batteries stop charging

The normal waveforms were shown the typical inductor CCM operation.
The "non-working charger IC" waveforms were shown the inductor DCM operation.
If the battery voltage increasing or setting a lower charge current, you could see CCM waveform changing to DCM waveform. So, both CCM and DCM waveforms are OK to our converter.
Please give detail about "non-working charger IC". For example: charge current regulation doesn't work or charge voltage regulation doesn't work...

1. Please check the battery voltage and charge voltage/current register value. If the battery is fully charged, the converter could have DCM operation.
2. Measure the Vsrp-srn to see if it reaches the limit or not.
2. Measure the Vacp-acn to see if it reaches the limit or not.

Hi Wang,

We're not seeing any charge current into the batteries, as measured by the charger IC, or by a current clamp over the battery supply wire.

We have a two cell setup. We're charging off of a 15V supply.

The "non-working" device has a two-cell battery voltage of 6.4V (nearly completely depleted, but replacing with a half-used cell doesn't fix the issue.

Our AC det voltage is 2.52V, and ACOK is pulled high.

ILIM voltage is set at 440mV.

Both the ACFET and the RBFET are enabled, and I do see the correct system voltage.

To answer your questions:
1)
After programming and reading back the registers I see:
0x12 - 0xF932 (Defaults, except for measure charge current)
0x14 - 0x07C0 (Set charge current to 1984mA)
0x15 - 0x20D0 (Set charge voltage to 8400mV)
0x3F - 0x0700 (Limit input current to 1792mA)
0xFE - 0x0040 (Manufacture ID)
0xFF - 0x000B (Device ID)

2) Vsrp-srn is 0V (both pins measure at the battery voltage) (On a working device, I do see a measurable difference)

3) Vacp-acn is 0V (both pins measure at the supply voltage) (Again, on a working device, I can measure a voltage drop)

Thank you for the detail info. It can speed up the debug work.
The "non working" board switching waveform shows
1. LoFET was always turned on first.
2. Less 10us between two LODRV refresh pulses.

To me, a. the converter is not latched off; b. refresh pulse too frequently;
Please check
1. BTST capacitor and HIFET. Is it damaged?
2. This issue is happened after replace IC. Can we re-solder the IC to avoid the soldering issue?

Thanks for working on this with me!

Here is the waveform of the LoDrv.  I do see the periodic refresh of the Bootstrap on the lodrv.

It does look like there is roughly 10uS between LoDrv pulses (waveform shows some ghosted captures).

I checked and replaced both the bootstrap cap (47nF) and the HiFET (SIS412DN) and get the same results.

I'm not equipped to replace the BQ IC.  I tried on another board and failed.  This board was working when it was initially assembled, so I'm not sure what has changed.  I also have 2 other boards that are exhibiting this same behavior.  Whereas roughly 10 are still working correctly.

Any more thoughts?

-Mike