BQ51050B: QI Power Transfer Continually Resets Shortly After Initiation

Robert McManus

Part Number: BQ51050B

We're having an issue utilizing the BQ15050B within our design. We're observing this seemingly "reset" behavior, as shown in the RECT line capture attached below. We monitored the V-drop over a resistor to infer the current and it seems to be possibly an instability once power transfer begins.

Another plot from a second device:

We've double-checked our calculations but are unsure of where the source of this instability is coming from. Do you have recommendations on where we should focus our efforts?

over 4 years ago

0 Anthony P Pham over 4 years ago

TI__Mastermind 23410 points

Hi Robert,

Welcome to E2E!

To narrow down the problem, would you be able to provide a schematic? Do you have information on the coil that you can share?

Here is one of our E2E FAQs on wireless power:

0 Robert McManus over 4 years ago in reply to Anthony P Pham

Prodigy 60 points

No problem, here's the QI charger portion of our schematic, below. The coil is a 27.9uH antenna we've tested successfully with the eval kit.

0 Robert McManus over 4 years ago in reply to Robert McManus

Prodigy 60 points

A second attempt to attach the schematic:

0 Anthony P Pham over 4 years ago in reply to Robert McManus

TI__Mastermind 23410 points

Hi Robert,

Thanks for providing a schematic. It looks like you have the TS/CTRL pin left open. This should be pulled to ground with a 10k resistor if the TS function is not going to be used. This will cause the shutdown when OUT/BAT turn on which may be what you're seeing.

0 Robert McManus over 4 years ago in reply to Anthony P Pham

Prodigy 60 points

Thanks Anthony. I apologize I didn't have that part of the schematic included. Please see the attached image that shows the TS/CTRL portion of our design, with a TDK thermistor, specifically:
NTC Thermistor 10k 3380K 0402 (1005 Metric)
It's from TDK: NTCG103JF103FT1

We've attempted one test to put a 10K load before with no change in behavior. However, we'll try it again. Thanks for the quick feedback!

0 Robert McManus over 4 years ago in reply to Anthony P Pham

Prodigy 60 points

See additional information in post below. TS/CTRL portion of schematic was earlier not included by mistake.

0 Anthony P Pham over 4 years ago in reply to Robert McManus

TI__Mastermind 23410 points

Hi Robert,

Thanks for the updated TS/CTRL portion of the schematic. There is a concern for the capacitor value that you are using for the TS/CTRL pin. The TS/CTRL pin uses a short pulse to measure temperature and the capacitor may be causing a slow slew rate which results in a temperature fault. Would you try with a smaller capacitor to reduce the capacitor charge time?

0 Robert McManus over 4 years ago in reply to Anthony P Pham

Prodigy 60 points

Thanks Anthony,

Your previous message caused us to reassess our TS/CTRL and we did find the capacitor we used was such a high level it was causing our issue. By simply removing the offending cap we stopped experiencing the resetting behavior. Thanks much!

I'm attaching images of our captures, showing the difference the capacitor has on our device:

And the waveform after removing the capacitor:

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BQ51050B: QI Power Transfer Continually Resets Shortly After Initiation