BQ24040: Current regulation problem

Fred P

Part Number: BQ24040
Other Parts Discussed in Thread: BQ25170

I have this square wave with 100ms period 50% duty cycle on ISET pin.

ISET has only a 1.8k resistor connected.

ISET2 is stable low (10k pulldown + powered down MCU giving 200mV on pin, ohmeter confirms 10k pulldown on pin). Shorting the pin to GND does not change behavior.

IN voltage is stable at 5.1V (USB powered). I have also tried with a USB3 and USB2 ports. Same bahavior.

Battery is LiPol chemistry and voltage is 3.7V.

I have tried with 2 different LiPol batteries and behavior is the same.

What's going on here...?

I also had a current regulation problem with a previous board revision. See thread: e2e.ti.com/.../bq24040-iset2-pulldown-value

Unfortunately, I was not able to take extra measurements to push this thread further.

Thank you for your assistance

over 1 year ago

0 Bill Johns over 1 year ago

TI__Guru* 75906 points

Hello

This could be battery detect circuit tripping. What is the battery voltage you see this at? If the battery is lower in voltage do you have this problem?

0 Fred P over 1 year ago in reply to Bill Johns

Expert 2235 points

3.6 to 3.8V

Did not test lower voltage as it behaves weird at nominal voltage.

0 Bill Johns over 1 year ago in reply to Fred P

TI__Guru* 75906 points

The other indication of a battery detect is a 25ms high low signal on the on the output which is similar to what we see in you scope capture.

If we do not see this at lower or higher voltage this is probably what unit is doing.

Increasing output capacitance has helped some customers.

Also the new devices BQ25170 do not have this issue.

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BQ24040: Current regulation problem