BQ25120: SW output won't get to 1.8v - stuck at 1.2v

Roee Tuval

Part Number: BQ25120

On startup, the SW output doesn't get to 1.8v. Instead, it exhibits a sawtooth pattern and eventually stabilizes around 1.2v.

We're using BAT input only (no VIN connected).

You can see the SW output after the inductor above and below the inductor (right out of the BQ) below:

This is a closeup of the SW output (first few cycles after power up):

This is the schematic:

Note that this is a Rev B of a design that already worked fine before. Nothing was changed in the BQ area - I'm trying to troubleshoot what would cause SW output to behave like that.

over 8 years ago

0 Raheem over 8 years ago

TI__Mastermind 21590 points

Hi,
I'm looking into this. I'll let you know when i have an answer.
Regards,
Raheem

0 Raheem over 8 years ago in reply to Raheem

TI__Mastermind 21590 points

Hi,
What is the laod when this occurs? Also what is the state of /CD?
Regards,
Raheem

0 Roee Tuval over 8 years ago in reply to Raheem

Prodigy 60 points

Hey,

/CD is floating - it is connected to a microcontroller that has no software programmed yet (and doesn't wake up due to the low voltage anyway, it's internally held at reset by the brownout circuit).

Load should be low, in the order of <10mA when 1.8v is reached. But because this is stuck at 1.2v, all components on the board are dormant and the consumption at the entrance to the circuit is <1mA.

Roee

0 Raheem over 8 years ago in reply to Roee Tuval

TI__Mastermind 21590 points

Hi,
Please pull /CD high and check to see if this issue persists.
Regards,,
Raheem

0 Roee Tuval over 8 years ago in reply to Raheem

Prodigy 60 points

Hey Raheem,

/CD is now pulled high and the issue persists.

Any other thoughts?

0 Roee Tuval over 8 years ago in reply to Roee Tuval

Prodigy 60 points

Ok, the plot thickens?

Taken with a microscope, what is this chip? PQ25120? ಠ_ಠ

Is this a real TI chip? I tried to validate against the marking on top but nothing comes up. TI, can you check this?

0 Raheem over 8 years ago in reply to Roee Tuval

TI__Mastermind 21590 points

Hi,
Looking at the schematic, you have VBAT connected to PMID. Please remove this connection. Also, do you mind sharing from which vendor you got this IC?
Regards,
Raheem

0 Roee Tuval over 8 years ago in reply to Raheem

Prodigy 60 points

Hey Raheem,

The VBAT net name is misleading, that's actually going to the components on the board which need direct battery power. The actual battery goes into the BAT test points in the schematic.

I do not know the source of this IC - it was purchased by a contract manufacturer in China. Going by the markings, is this a legitimate TI part?

Thanks!

0 Gautham over 8 years ago in reply to Roee Tuval

TI__Genius 12485 points

Roee,

We were able to trace the marking to a TI part but however, the PQ marking is typically pre-production.

Released units will have a BQ marking. Can you apply for sample and try the units from the release pool?

regards,
gautham

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BQ25120: SW output won't get to 1.8v - stuck at 1.2v