BQ24193: Seeing spikes on charger output from a low battery

Hi,

1. What is the battery voltage you referred as "the battery is almost depleted"?

2.  You mentioned "the charger starts pulsing from 3.5V to 4.0V", which output are you referring to? VSYS or VBAT or something else? Is the pulsing one time or repetitive?

Thanks,

Ning.

Good morning,

1)  When out battery is fully charged, it outputs about 4.1V. A low battery for our system outputs about 3.4V.

2) The output I am referring to is the Vsys output. The pulse occurs repetitively. At just about 2 Hz.

Regards,

Irenz

Hello,

We are still investigating this issue and found some more information that may help find a solution. 

1) We lowered the fast charge current limit to about half of the original value from 1.5A to 700mA in order to stabilize the charger. 

2) Having a battery with about 3.6V or lower would start showing this behavior, but a battery of 3.7V or higher does not. 

Regards,

Irenz

Here are some more updates,

On the scope capture below, you can see a zoomed in transition of the charger output on the SYS pins during the increase in voltage.

The noise surrounding this is actually seen on the ground plane as well. The top line is connected to ground.

Irenz,

1. Could you please provide all register values when VSYS is stable and when VSY has pulse respectively?

2. Does the behavior show on one IC or multiple ICs?

Thanks,

Ning.

Hi Ning,

1. These are the registers we set by default in our system:

   REG00 - 0x35

   REG01 - 0x5B

   REG02 - 0x40

   REG05 - 0x8A

   In order to stabilize charging on the boards exhibiting the pulses, we had to change REG02 to 00 to set the fast charge current limit to 512mA. 

2. We saw this behavior occur on multiple boards with this particular IC on our new design. We've used this IC on a previous design and it worked. However, the changes should not have added much to the load. 

Regards,

Irenz