BQ51003: I don't get a Qi lock on all PCBs in the same batch.

Peter Agius

Part Number: BQ51003

I have used the suggested BQ51003 circuit from datasheet (and development board) but only get a lock on around 5 out of 10 PCBs in a prototype batch.

3 different off-the-shelf Qi TX units do the same.

Attached :-

- RX circuit schematic jpg

- datasheet for the RX coil being used

- signal on BQ510003 output where you can see it starting to talk and get up to speed but then turns itself off and starts again

- feeds MCP73833 battery charge controller with limit set to 200mA

- still no lock if the battery is fully charged and the circuit is turned off so that it's virtually no load

Any ideas for what I can try to fix this?

Thanks.

over 6 years ago

0 Peter Agius over 6 years ago

Prodigy 70 points

Attachments Coil - Farnell 2367225.pdf

0 Bill Johns over 6 years ago in reply to Peter Agius

TI__Guru* 76446 points

Hello
Double check the installation of R49 and Q5 (AD & AD-EN) -- If R49 is installed it will cause unit to turn off when output is enabled.

0 Peter Agius over 6 years ago in reply to Bill Johns

Prodigy 70 points

R49 definitely not fitted. That's just a back-up if we couldn't get the Qi to work (or Q5 to switch) so that we could revert to a direct charge option. The boards that don't Qi lock do correctly switch Q5 if volts are put on the Charge+ input which confirms a) the AD and /AD-EN connections are correct and b) the BQ51003 bga chip is correctly fitted and functioning (and also you can see there's comms between TX and RX which shows it's trying to lock). Do TX units send any diagnostic info out of the USB connection or is that just power?

0 Bill Johns over 6 years ago in reply to Peter Agius

TI__Guru* 76446 points

The TX will not send any diagnostic.

At the time the RECT voltage drops is about the time output is enabled. The RECT voltage is adjusted to 7V and then the output is turned on.
What does output voltage do during this time?
Looks like current limit is set to about 300mA.

The coil tuning needs a little adjustment. Coil L is about 27uH and C is 68nf/68nf/47nf (C24/C29/C39) this is high of the 100kHz target. Needs to be about 47nf/47nf.

0 Bill Johns over 6 years ago in reply to Bill Johns

TI__Guru* 76446 points

Hello Peter
Any update on this one?

0 Peter Agius over 6 years ago in reply to Bill Johns

Prodigy 70 points

Hello Bill, Thanks for keeping me in mind! I've been a bit side-tracked since the weekend but hope to try some different caps shortly.
Will keep you posted. best regards Peter

0 Peter Agius over 6 years ago in reply to Peter Agius

Prodigy 70 points

Hello Bill , Apologies for not getting back to you before now. I am now back looking into this and will give you an update shortly. Please keep this thread open for now. Peter

0 Bill Johns over 6 years ago in reply to Peter Agius

TI__Guru* 76446 points

Hi
We can work this problem offline.
Look for a message from me.

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BQ51003: I don't get a Qi lock on all PCBs in the same batch.