BQ24650: Battery won't fully charge

Hi Katrina,

   What is the status of STAT1 and STAT2 on the board that doesn't fully charge? Have you checked through for possible fault conditions?

STAT1 is low, STAT2 is high and continuously stays this way.  I let the battery charge overnight.  What sort of fault conditions would not be reported by the STAT pins?

I have a couple of questions to verify that my understanding of the functionality of this IC is correct:

1. How should the STAT1 and STAT2 pins respond to the battery detect feature?

2. In my design, the Current sense resistor is 0.05 ohms to cap the charge current at 0.8A (which is appropriate for the lead-acid battery I am charging).  Based on the datasheet, it will go into Discontinuous Current Mode regularly since the termination current is 0.08A, resulting in a voltage across the sense resistor of 4mV.  Is this a problem?

Would there be something that would cause STAT1 to blink?  That is what I am seeing.  When I try to measure VFB, the STAT2 pin blinks rapidly ands STAT1 goes low.  I say blink because they are connected to LEDs.  Also, the board version I had before this one worked well--the LEDs were off when not connected and indicated charged and charging correctly.  The only thing I changed for the new version was how the LEDs interfaced with STAT1 and STAT2.  The circuits are shown below (first one has issue, second one is good--I also know polarity is inverted).  The only other thing I changed was filling the top and bottom layers with ground.

Hi Katrina,

   The VFB node is sensitive to attaching multimeters and scope probes. The wires/probes have their own capacitance and inductance which can interfere with the sensitive feedback regulation pin. Does it happen when you don't have clips on the VFB node?

Ok well that explains that!  Though yes, on the board with the issue, STAT1 blinks when there is no probe on VFB and no battery connected.

Can you take a scope capture of VCC, SRN, PH and STAT1 when there is no battery connected?

Here are the requested pictures.  The order is VCC, SRN, PH, STAT1.  The last picture has PH (pink), SRN (blue) and STAT1 (green) in one capture so you can see the related timing.

Hi Katrina,

   This behavior doesn't look right. Your VCC has a huge ripple even though there is no load, and it looks like something is limiting your adapter and the PH signal is not as expected, as a result. Do you have a current limit on your input source?

My input power source for this board is 3 AC-DC current sharing power supplies (PN: IRM-90-12).  The max current out put of each supply is 6.7A.  What makes you think it is current limited?  BTW--In order to capture enough information on the oscope i had to sequence the readings--not sure if that contributes to the strangeness you are seeing.

Hi Katrina,

  Something is incorrect with this battery absent detection shown in the scope captures. Can you test your input source with an EVM and take a scope capture of the battery absent scheme? I don't see anything incorrect with the schematic. Figure 20 of the datasheet is expected behavior.