BQ24650: Shortcircuit of SRN, SRP, VFB pins to GND

Dawid Weglarz

Part Number: BQ24650

Tool/software:

Hello, our company designed a board that hosts a Raspberry CM4 and we implemented a solar charger using BQ24650RVAT.

The design itself is nearly identical to the one proposed in the datasheet but for some unknown reason the board is not working.

Our engineer made some checks and discovered that the pins SRN, SRP and VFB are all connected to ground causing a shortcircuit when given power.

In fact we tested it and the SRP track blow up. I hope someone can provide some more insight on this problem.

Our current design for the charger:

6 months ago

0 Christian Moyer 6 months ago

TI__Mastermind 31966 points

Hello David,

I'm not sure if this is the cause of the issue, but you should not have the 22uF cap between SRP and SRN.

Please put SRN signal before the 22uF, this might be what damaged the board.

Best Regards,

Christian.

0 Dawid Weglarz 6 months ago in reply to Christian Moyer

Prodigy 10 points

Hi Christian, I've double checked the datasheet and I think the connection is the same in that schematic (page 23). I'm missing something?

0 Dawid Weglarz 6 months ago

Prodigy 10 points

Additional info:

All the board have the V_BAT shorted to GND until we remove physically the BQ24650 from the board.

0 Christian Moyer 6 months ago in reply to Dawid Weglarz

TI__Mastermind 31966 points

Hello Dawid,

Dawid Weglarz said:
Hi Christian, I've double checked the datasheet and I think the connection is the same in that schematic (page 23). I'm missing something?

The BQ24650 is a legacy device, so I'm not really sure what value that C8 is, I think it's for common mode filtering and should be around 0.1uF. I would not recommend having the output cap before SRN, because it could affect the charge current accuracy. I also recommend refering to our BQ24650 scheamtic checklist:BQ24610_BQ24650_Schematic_Checklist (53).pdf

Have you replaced the IC, Could it have been damaged?

Best Regards,

Christian.

0 Dawid Weglarz 6 months ago in reply to Christian Moyer

Prodigy 10 points

We tested 2 boards powering them with different methods with same result. The system is designed to be connected to AC and a solar panel at the same time and switch to solar when AC is not present (we are using the same IC to handle both sources). I'll check with our engineer and send them the schematic.

0 Christian Moyer 6 months ago in reply to Dawid Weglarz

TI__Mastermind 31966 points

Hello Dawid,

Dawid Weglarz said:
The system is designed to be connected to AC and a solar panel at the same time and switch to solar when AC is not present

The BQ24650 can not support AC power, it can only support DC.

Have you confirmed that this is not soldering issue and that these two pins are not shorted

Best Regards,

Christian.

0 Dawid Weglarz 6 months ago in reply to Christian Moyer

Prodigy 10 points

My bad, I meant DC. Anyway I checked and the two pins are shorted and removing the IC fixes the short on the whole board so presumably it's an board issue more than a schematic/logic one. Have you any tips on how the solve it? Are there any tolerances we missed? Because of 4 boards we have all present the same issue. Thank you

0 Christian Moyer 6 months ago in reply to Dawid Weglarz

TI__Mastermind 31966 points

Hello Dawid,

Do you have your PCB file? There may be an issue with the connection.

Do you see any solder short on the pins?

Best Regards,

Christian.

0 Dawid Weglarz 6 months ago in reply to Christian Moyer

Prodigy 10 points

I don't see any visibile shorts on the IC pins itself and neither on the pads on the board where we removed it.

0 Dawid Weglarz 6 months ago in reply to Dawid Weglarz

Prodigy 10 points

We conducted some further checks on the PCB, and can confirm that the footprint we used for the BQ24650 is too small. Even if it should be a standard footprint, the actual footprint differs slightly. As a result, the pad designated for thermal dissipation beneath the chip, once soldered, short-circuits multiple pins to GND.

Power management

Power management forum

BQ24650: Shortcircuit of SRN, SRP, VFB pins to GND