Problems setting up the STWLC38

[ggeorge_42]

Hello,

We plan to use the STWLC38 for power in a new wearable design.

We purchased the STEVAL-WLC38RX and STEVAL-WBC86TX kits to get familiar and experiment with the ICs.

Now we are trying to adapt the Rx of the STEVAL-WLC38RX as used in a wearable device and followed the application diagram from the STWLC38 datasheet (Figure 13. STWLC38 basic application diagram in Rx mode), using the recommended coil (Wurth 760308101219). We also changed the Cs and Cd capacitors as recommended.

The STEVAL-WBC86TX board was not modified.

The problem is that the power reception from the STEVAL-WBC86TX is not enough to reach 5V at the output.

We tried changing the Cs according to STDES-WLC38WA (TN1440) as well as some other values with better results, but not enough. In the  chart of WPSTUDIO Vrect looks unstable, with lots of ripple and Vout is OFF.

Do you have any suggestions on how to tune the Rx circuit with the new coil?

Thank you,

G.Giannopoulos

[willzhou]

Hi
1.What is your distance between TX and RX?

2.About STDES-WLC38WA (TN1440) recommend CS,

"We also changed the Cs and Cd capacitors as recommended." what does Cs and Cd changed?

STDES-WLC38WA recommend CS=247nF
CS1, CS2 = 100nF
CS3 = 47nF
CS4 = N.M.

STDES-WLC38TWS recommend CS=300nF
CS1, CS2, CS3 = 100nF
CS4 = N.M.

RX coil specifications use Inductance 11.8 μH, dimensions Φ15 mm

What is your rx coils?

3.How about you set high voltage in TX, usually you set to 5V, can you change to 6V or higher to check?

4.What is RX fw version, please give below picture to me.

5.what is the volume of wearable design? if volume is large, i can contract local FAE to send STDES-WLC38WA board for test.

 

[ggeorge_42]

Hi, here are some answers:

1. The distance between Rx and Tx is 3-5mm.

2. The Cs values as you say.

The Rx coil is Wurth 760308101219, https://www.we-online.com/components/products/datasheet/760308101219.pdf

Inductance and dimensions as you say.

3. I will try to set the Tx voltage and report the results.

4. My Rx fw version is:

5. The wearable will be a small watch, but we have not built it yet. We are experimenting with the evaluation boards to finalize the design.

[willzhou]

Thank you

About chart of WPSTUDIO Vrect looks unstable, with lots of ripple and Vout is OFF
1.Please save GUI charts data and i can see vrect value and other values.

2.So you modify board and use Wurth coils put on tx and test, can you share your test picture, so i can see tx and rx board.
3.Please use attach cfg file and use GUI tool program it to test again.

 

 

[willzhou]

Hi
1.You can google FT260 driver or find at this link
https://github.com/STwirelesscharger/Python_FT260_ST_WLC

2.TX SS TO (Signal Strength or Ping Timeout). This probably has to do with the coupling of Tx/Rx coils (very different diameters)
Yes it is, coupling is bad and tx can not decode SS packet