BQ500212AEVM-550 or BQ51050BEVM problems

Hello user3556070,

In order to find out what is going on, please provide the following information:

1. Did you modify anything on the EVMs? Did you set another value for IILIM or replace the RX coil? The default charge current setting for the bq51050B is 1A.

2. Could you provide a scope shot of the RECT and BAT pins at startup?

3. What is the battery voltage on initial insertion and where was the battery attached on the EVM? Could you provide a photo of your test set up? If the RED LED of the TX is on, this may indicate a FOD failure. Did you change your ROS or RFOD?

Best Regards,

Markus Fleck

Hello Markus,

So,

I didn't modify anything on the EVMs.
The coil RX still the same.
 I just ask about the coil because I would like to use small coil on the future application.

The battery had 2.7V, 4.2V on initial insertion. The both way the same result.

I'm sending some photos.

I read the datasheet and I couldn't figure out the expression of BAT and PS.

Where is that pin?

Hello user3556070,

Thanks for providing this material.

To charge a battery with the bq51050BEVM, the battery should be tied like this: BAT+ to J3(OUT), BAT- to J4(prefer J4 over J2 although it`s the same node).

J1(+) and J2(-) is for an additional DC supply. The RX will then choose either the wireless charging source or the DC supply depending on the setting of Pin EN2. (see datasheet for details).

If you change the receiver coil to a smaller one it may require Cs/Cd changes. A 10mm coil will probably be too small for the standard Qi TX coil. If you use a smaller coil than the standard Qi coil your TX design will not be Qi compliant. TIDA-00334 (for a 30mm TX coil) and TIDA-00318/319 give an example of smaller coil design.

For your RX EVM, please set JP3 to Disable and JP2 to High. Please also make sure that your battery voltage is below 4.2V. It´s not expected that this causes the problem but I want to exclude it though.

The setting of JP6 on your EVM is ADJ. Which resistance value did you set for the potentiometer R16?

Could you provide scope shots of TP12 (RECT) and TP7 (BAT) on the RX at startup and connected battery? The RECT pin voltage often gives a clue what´s the problem.

A flashing RED LED on the TX usually indicates a FOD fault warning but I would exclude this at the moment since you didn´t modify the EVM´s.

Best Regards,

Markus Fleck

Hello Fleck,

Thank you.

Now is working,...maybe.

I changed the value of R16 to 600 ohms, and the D5 Led starts to blink.

I'm sending the waveform anyway. The first one is without a battery and the second one is with battery.

Question. How can I calculate the R16 value?

Hello user3556070,

The charge current IBULK can be calculated by RILIM = KILIM / IIBULK (see p. 19 in Datasheet).

RILIM is R16 + RFOD. The FOD resistor is fixed and at this EVM set to RFOD = 200Ω and KILIM = 314. So if you set your R16 to 600Ω, you will get a charge current of about 393mA = 314/(600+200). For example if you want a charge current of 800mA, use the equation like this R16 = (314 / 0.8A) - 200Ω. R16=193Ω.

You could also set the JP to FIX which gives you a charge current of about 1A.

Please let me know if this works for you.

Best Regards,

Markus Fleck

Hello Fleck,

Thanks for your reply.

Now it's working fine.

But I disagree with the equation.

The bq51050BEVM-764 User's Guide pg8, said that the value of R16 is JP6-ADJ to J2(GND).

That's not the real value of R16 but R16+200ohms right?

So, if I set that value to 600 ohms, I will have 314/600=523mA,...

but it's not true,...where did get KILIM=314? The datasheet said 300!!

So, I calculate again and tested on my kit.

1. JP6-ADJ to J2 = 600 ohms (R16+200)

2. I = 300/600 = 500mA

3. Measured with ammeter  I got 497mA (average)

Hello user3556070,

You´re right. If you measure the resistance of JP6-ADJ to J2-GND then it´s R16+200Ω.

The KILIM value in the datasheet is being updated to change from 300 to 314.

The reason why you measure 497mA (average) is because the current decreases slightly when it comes to communication of the RX and TX.

The scope shot below shows an output current of about 520mA of the bq51050/51B. The average current will be slightly lower.

Best Regards,

Markus Fleck

Hi Fleck.

Thanks a lot.