BQ21040: #CHG pin never goes inactive when charge current goes below termination current

Hello Viggo,

We suspect the device may be going into Vin-DPM when powered with wireless charging receiver. I will try to test this and get back to you.

In the meantime, could you try to provide a scope capture of Vin and Vout? If Vin drops, this is an indication of Vin_DPM.

(See Section 8.4.2 in the data sheet for more information on DPM)

Hello Diana, thank you for your quick answer.

pls find attached scope dumps. I don't think the Vin is dropping enough to enter VIN_DPM.

Changing capacitors on Vin and Vout from 1uF to 10uF did'nt solve the fack, that the charging is never terminated and the #CHG output is never deactivated.

From my Microsoft Internet Explorer 11 I can't read the inserted file "bq21040 charging from bq51013B supply.pdf" I hope you can.

bq21040 charging from bq51013B supply.pdf

 

Hello again,

I have got a new receiver Würth 760308103205 wich works a bit better than my own handmade.

But the bq21040 #CHG keeps activated even when the terminating current is passed.

Pls see attached scope dumps.

Regards

Viggo

Hello,

for your kind information:

monitoring the charging current, when the current passes the termination value ~20mA shows that the charging is terminated.

Current is measured by measuring the voltage accross a 20milli ohm resistor in series with the lipo.

pls see attached graph.

bq21040 termination current.pdf

ups forgot to mention the most important fact in my last post with the graph
- the #CHG output of the bq21040 is still activated, ie low, when the charging current drops, and I have checked with my finger on the probe ;-)

Hello Viggo,

Thank you for your well-labeled waveforms and graph. So the problem now is that charge current terminates but CHG stays low?
And this only happens with wireless charging? Have you tested this with more than one unit?

Here are two things to consider

1. What is the circuitry that #CHG arrow is connected to on your schematic? You could try using an LED in series with R22 to see if the extra circuitry is causing the problem.

2. Does the input 5V from the wireless receiver ever have dropouts? A dropout would start a new charge cycle, for which CHG will be active

Hi Viggo,

Did you ever make progress with this issue?