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BQ51051B: Low Battery Charge Issue

James Hook1

Prodigy 80 points

Part Number: BQ51051B

Hi,

I'm testing my latest prototype using the bq51051b device and have encountered a problem with a low voltage battery, please see below traces for RECT and BAT pins, RECT seems very high and I'm not sure what is causing the issue, the CHG light is very dim also, any assistance of what the issue is I'd be very grateful. Circuit used also below, I'm using a 760308101309 coil from Wurth.

over 5 years ago

0 Bill Johns over 5 years ago

TI__Guru* 75906 points

Hello

This looks like the RX cannot tune the TX to right operating point. The RX stops sending control error packets, gives up on the TX.

What coil are you using?

0 James Hook1 over 5 years ago in reply to Bill Johns

Prodigy 80 points

Hi Bill,

Thanks for the response, I'm using a 760308101309 coil from Wurth.

James Hook

0 Bill Johns over 5 years ago in reply to James Hook1

TI__Guru* 75906 points

Hello

I have not used the 760308101309 coil. It is a small coil that has a low L value. Will need good alignment with the TX and low coil to coil distance.

A coil I have used is the 760308101303---26mm RX coil, the L value is high and this is good in a small coil.

If the coil L changes the series capacitors need to be retuned.

0 James Hook1 over 5 years ago in reply to Bill Johns

Prodigy 80 points

Hi Bill,

Thanks I will try the suggested coil and have updated my tuned caps calculations. I will let you know if this cures my issues.

Thanks

James Hook