BQ25672: No output, no charge on VBUS

Tomasz Zygulski

Part Number: BQ25672
Other Parts Discussed in Thread: BQ25792EVM

Hi,

I've a design with the charger with marking 14A90Z8. When VBUS is applied without the battery connected after 155 ms the REGN turns on at 2V and switches off after additional 85 ms. It does that for 7 times with 500 ms in between and then stops. There is no output on SYS. When I plug in the battery there is output on the SYS and when VBUS is applied the battery doesn't charge and no output on the REGEN. Attached is the schematic and REGN behavior on VBUS only. Battery is 4S and VBUS is 24V but tested from 16V to 23V. Could you please guide me what might be the reason?

By the way, I've seen a thread that there was a faulty series of the bq25672's, could you please also verify that this behavior is not related to that?

Thanks,

Tomasz

11 months ago

0 Jeff F 11 months ago

TI__Guru**** 150335 points

Hi Tomasz,

The charger is detecting a fault of some kind and entering HiZ mode after 7 startup attempts. I do not see any obvious issues with the schematic except for protection against damage from hot plugging the input voltage > 15V or the 4S battery pack. I suspect the IC is damaged from either ringing above 30V at input plug in or above 20V at battery plug in. The latest datasheet has recommendations for adding an input snubber at VBUS and a TVS diode at BAT to prevent damage.

Regards,

Jeff

0 Tomasz Zygulski 11 months ago in reply to Jeff F

Prodigy 30 points

Hi Jeff,

Turns out there was an issue with the soldering from factory, however now, the RGEN starts and stays on at 5V, but I see only 2V on the SYS output and with battery it's still not charging it. Any ideas?

Best,

Tomasz

0 Jeff F 11 months ago in reply to Tomasz Zygulski

TI__Guru**** 150335 points

Hi Tomasz,

Is there a switching waveform at SW1 or SW2? Can you read the status and fault I2C registers?

Regards,

Jeff

0 Tomasz Zygulski 11 months ago in reply to Jeff F

Prodigy 30 points

Hi Jeff,

I don't have any waveform on the SW pins, steady 2 V. Right now, I don't have a possibility to read the registers, I'm leaning towards a combined issue of PCBA issues with a damaged IC due to hot plugging. I will add the protection, replace the IC and go from there with troubleshooting.

Thanks,

Tomasz

0 Jeff F 11 months ago in reply to Tomasz Zygulski

TI__Guru**** 150335 points

Ok. Keep me posted. I'll close this ticket for now. It will lock in a couple of weeks so you might have to enter a new post.

Regards,

Jeff

0 Tomasz Zygulski 11 months ago in reply to Jeff F

Prodigy 30 points

Sure, could you tell me if you have any specific TVS diode that you recommend, or its parameters at least? I noticed that the datasheet on the TI website recommends a capacitor on the battery positive line. Is that the older datasheet?

Best,

Tomasz

0 Jeff F 11 months ago in reply to Tomasz Zygulski

TI__Guru**** 150335 points

Hi Tomasz,

The capacitor on BATP can be used instead of the TVS if a external shipFET is installed. The link below gives a tutorial on TVS diodes.

Transient Voltage Suppressor Tutorial and Applications (apogeeweb.net)

In short, you need a TVS diode with VBR <=20V. The BQ25792EVM schematic shows one option

Its a bit of overkill but works great for 4S application.

Regards,

Jeff

0 Tomasz Zygulski 10 months ago in reply to Jeff F

Prodigy 30 points

Hi Jeff,

Thank you for the suggestion. After replacing the IC with a new one from DigiKey and adding the protections it works, charges the battery and powers the system, but the charging current with the battery at 15.2V is about 90mA. I will troubleshoot it later, but any idea why it might be like that?

Best,

Tomasz

0 Jeff F 10 months ago in reply to Tomasz Zygulski

TI__Guru**** 150335 points

Hi Tomaz,

Can you read the status and fault registers and also enable the ADC and read all of the ADC channels? I can help debug from there.

Regards,

Jeff

0 Tomasz Zygulski 10 months ago in reply to Jeff F

Prodigy 30 points

Hi Jeff,

Attached are the registers, let me know what you think.

Thanks,

Tomasz

0 Jeff F 10 months ago in reply to Tomasz Zygulski

TI__Guru**** 150335 points

Hi Tomasz,

The registers are showing that the charger is in taper charge meaning V(BATP) = BATREG. What is the charger's BATREG register setting? Also, the ADC channels were all zero. Can you rerun with EN_ADC bit in REG0x2e[7] = 1?

Regards,

Jeff

0 Tomasz Zygulski 10 months ago in reply to Jeff F

Prodigy 30 points

Hi Jeff,

In the previous read the battery was disconnected as it turned out, sorry for that. This time it is connected, and ADC is enabled.

Best,

Tomasz

0 Jeff F 10 months ago in reply to Tomasz Zygulski

TI__Guru**** 150335 points

Hi Tomasz,

The charger is reporting IINDPM which is limited input current but that does not make sense with for the ADC values:

If you short VBUS to PMID, does the charge current increase? If so, then the FET and current sense amplifier between VBUS and PMID is damaged, possibly due to input hot plug.

Regards,

Jeff

0 Tomasz Zygulski 10 months ago in reply to Jeff F

Prodigy 30 points

Hi Jeff,

Shorting the VBUS and PMID does not increase the current at all.

Best,

Tomasz

0 Jeff F 10 months ago in reply to Tomasz Zygulski

TI__Guru**** 150335 points

Hi Tomasz,

Do you all boards/ICs do this are only one? If multiple, can you send me a scope shot of SW1 and BTST1 when this occurs?

Regards,

Jeff

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BQ25672: No output, no charge on VBUS