BQ51003: Rect pin issue

Thomas Gross56

Part Number: BQ51003

Hello,

I have used the TIDA-00318 reference design for a wireless battery charger. Unfortunately on my custom PCBs the design is not working, output from the BQ51003 is between 0.5v and 1v.

After rechecking my design I have realised I haven't connected the two RECT pins to each other, would this alone be enough to cause my issues?

Kind Regards

Thomas

over 7 years ago

0 Bill Johns over 7 years ago

TI__Guru* 75656 points

The RECT pins are connected internally and this should not be a problem.
If voltage a RECT pin is low it could possibly be caused by the RX coil or coil tuning. Check voltage a AC1 & AC2 to ground. During digital ping this voltage should be increasing to greater that 2.7V (UVLO).

0 Thomas Gross56 over 7 years ago in reply to Bill Johns

Prodigy 70 points

Thanks for the information Bill, I have only been able to test again today. Below shows my scope readings from the AC1, yellow, and AC2, blue. AC2 is peaking at roughly 2.5v but AC1 barley goes over 2v.

Below are a schematic and board layout of the relevant sections.

Any more advice on where my problem could be would be really appreciated.

Thanks

0 Bill Johns over 7 years ago in reply to Thomas Gross56

TI__Guru* 75656 points

What RX coil are you using and what is the coil to coil distance?

0 Thomas Gross56 over 7 years ago in reply to Bill Johns

Prodigy 70 points

Here is the data sheet sheet for the coil: IWAS4832ECEB220J50.

The coil to coil distance is roughly 5mm.

Thanks

Thomas

0 Bill Johns over 7 years ago in reply to Thomas Gross56

TI__Guru* 75656 points

The problem may be the RECT pins. If one of the two is connected to the Vrect capacitor you are OK. But it look like you have no filter capacitor on Vrect.

The RX coil and distance look OK. May need to adjust the tuning.

0 Thomas Gross56 over 7 years ago in reply to Bill Johns

Prodigy 70 points

You are correct, I don't a filter capacitor connected to the RECT pins. Will this be the cause of my issues?

Thanks
Thomas

0 Bill Johns over 7 years ago in reply to Thomas Gross56

TI__Guru* 75656 points

Yes this will cause problems.
The RECT pin is output from full wave bridge and input to housekeeping voltage regulator and output LDO. With no filtering the very high ripple will cause problems.

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BQ51003: Rect pin issue