BQ24610: What prevents charger from fast charging.

Hi Mike,

      The battery voltage is anywhere from 6.8V to 7.3V when it shuts off. I can get it work at pre-charge rate by resetting CE. The input to the charger is +24V. I just changed the resistors in a EVM to my design values for 2 cell operation. The EVM charges the same battery at the proper 1.3 amps as soon as I turn it on. This proves the battery/thermistor is functioning correctly. The 1.75V,  I mentioned earlier was the VFB pin. I ordered some 6.8uH inductors to substitute for the 10uH, but they won't be here until tomorrow.  Any more help would be appreciated! Thank You!

Here is the Inductor switching waveform (Blue) and the battery pre-charge current waveform (Green). 

Thanks for looking!!!

Hello,

This waveform is consistent with non-synchronous mode caused by the light load. I have several questions however.

1. What is your TTC capacitor? This affects the fast charge safety timer.

2. I am confused why your current is only 130 mA when you are above LOWV. If you are above LOWV you should be in fast charge. Can you please confirm the VFB voltage and the output current that you are observing? What is different from this case to the one where you plug it in and 1.3 A starts as soon as you turn it on? Can you please tell me your resistive divider for the VFB pin?

Thanks,

Mike Emanuel

Please click "Resolved" if this answered your question.

Hi Mike, 

1. TTC capacitor is 47nF

2. Yes, we are above the LOWV because VFB is 1.75V and it should be fast charging and it isn't, this is my main problem. The difference 

when it start at 1.3Amps, is I transferred my settings (ISET1/2) to one of TI's Evaluation Boards to prove my battery/thermistor was good.

The Evaluation board works perfect with my resistor values. My design only does pre-charge! My divider is 300K connect to VBAT and the other end connects to VFB and a 100K resistor to ground. The upper 300K resistor has a 27pF feed-forward capacitor in parallel with it? 

Thank you for your time!

Hello,

Can you please send your schematic? This would simplify the debug.

Thanks,

Mike Emanuel

Hi Mike,

Hello,

I am having trouble reading your schematic. Can you post a clearer schematic?

Thanks,

Mike Emanuel

How do I attached a PDF?

Thanks!

Hello,

Click Insert->Image/video/file->Upload.

You're welcome!

Sincerely,

Mike Emanuel

CHRG.pdf

Thanks for helping! I am getting 6.8uH inductors today to try.

Thanks again!

Hello,

Can you send a scope capture of the input voltage, SRN voltage, PH voltage, and charge current while the issue is happening?

Thanks,

Mike Emanuel

Here is the waveforms you requested.

Thanks for helping

Here is a better picture, charging at 0.13 amps but still not high rate?

Hello,

Thank you for that information. Can you please report the TS voltage, the VREF voltage, the CE voltage, STAT1 voltage, STAT2 voltage, PG voltage, and REGN voltage when this is happening? I need to make sure everything is biased correctly.

Thanks,

Mike Emanuel

Hi Mike,  

TS=1.661V, VREF=3.329V, CE=3.290V, STAT1=0.003V, STAT2=3.289V, PG=0.003V, REGN=6.02V

ISET1=0.263V, ISET2=0.133V,AC SET=0.52V

Thank you again for helping?

Hello,

Have you verified the full charge voltage to be 8.4 V?

Also, how did you probe the PH and SRN nodes in the last scope capture? I see that there are transients on the battery voltage up to about 12 V and on the PH node of about 34 V. For a battery voltage of 8.4 V, this would be a battery overvoltage. In addition, the PH node peak is above the recommended value of 30 V and is approaching the absolute maximum value of 36 V. Layout could be affecting these transients.

Thanks,

Mike Emanuel

The noise is probably from long ground leads (4inches). I can't make a tight spring tip ground  measurements on more then 

one signal at a time. Have no techs and working at home. My BATA_GND is a island on layer 2 of a 8 layer board. 

How does the EVM tie power and analog ground nets together, just at the power pad only? Thanks again!

Here is a tight ground tip picture of VCC, AC coupled to increase sensitivity. 150mV p-p noise, should be good!  Thanks!

HI Mike, added a 680pf snubber across the PH node to ground kill the overshoot and it started charging at 1.34AMPS!!!!! Held the  cap with

one hand and scope probe with the other, will solder it in next. Hope this works, thanks for leading me to it! I will let you know!