bq51003 Output Power Cycling

Craig,

What is connected to the OUT pin of the bq25100H?

Can you view the OUT and RECT pins on the bq51003 with a scope?

What is the current limit set to on the bq51003 and the charge current on the bq25100H?

Any modifications made to the reference designs for the two devices?

Regards,

Dick

Thanks Dick,

Here are my responses

What is connected to the OUT pin of the bq25100H?
--I either have it open or connected to a power supply that can source. The current I am seeing is around 35mA when connected to a power supply (going in to the supply). The ILIM resistor is 4.99k and RFOD is 200 Ohm. So I am assuming around a 60mA current limit

Can you view the OUT and RECT pins on the bq51003 with a scope?
---Yes, I can do that and get you screen shots.

What is the current limit set to on the bq51003 and the charge current on the bq25100H?
---ILIM to 60mA as mentioned above.
---Charge current is 50mA

Any modifications made to the reference designs for the two devices?
--No

---Also, I noticed that this does not happen when I add more of a gap between the charger and the coil. Can the coils be too close?


Thanks

Craig

Craig,

Your current setup sounds reasonable.  You should have 50mA, as you note, when connected to a source meter (sinking current).

The distance between the coils does have an impact.  What coil are you using for the RX?  Size, Ls and Ls' are the key components.  It's all about the coupling.  The spacing is important especially in relation to the coil ratio (TX : RX).

Regards,

Dick

Hi Dick,

I'm using the Wurth 760308103204 for the RX coil. The TX side is an off the shelf charger so I don't know the coil size inside.

It's pretty consistent that I can get it to work with a slight gap and not work when up against the coil. Do you know why this might be?

I don't think it will be an issue since eventually I will have an enclosure in between the coils. But if this is an issue in the future is there a way to solve it?


Thanks

Craig

Craig,

The system is configured for an optimum spacing based on the TX and RX having specific spacing.  The WPC specification gives requirements for the TX coil size (using a certified transmitter tells me a lot about the coil) and the distance from the top of the coil to the top of the industrial design.  The spec also gives a range for the RX spacer.  What you'll find is efficiency differences as you play around with that spacing.  A simple test I've done is by using business cards to increase / decrease the z-distance.  You can find an optimized spacing there.  Additionally, as you build your system around the coil, you will impact the system performance.  

The coil you are using is a solid coil I have used for evaluation and characterization.  

Regards,

Dick

Hi Dick,

We are still having issues with this. Would if be possible for me to send you a schematic offline to review?


Thanks

Craig

Craig,

Yes, that would work.

Regards,

Dick