I just started to connect a 3.7V battery, with the programmed charge current of 1A. When I connect the eval board module directly to the battery the red LED glows and the PG LED glows. All is working fine.
Now I want to view the charge current through a series multimeter on the VBAT output, so I inserted a series multimeter on the output and tried to measure the charge current.
When I did this, the charge current displayed on the multimeter is 650mA and then keeps decreasing slowly. I tried to maintain short leads to measure the current. The red LED does not glow, indicating that charging is not happening. The green LED is glowing.
What might be the reason for this behavior? Can someone provide an idea?
To cross-check on what is the problem, I removed the series multimeter. Connected the Eval module directly to the battery and placed a current probe and measured on the oscilloscope. Now, with this setup, the charge current of 1A is clearly visible.
So, when the output battery charge current is measured by inserting a series multimeter (10A current setting), the charging is not happening properly. But when I do the non-invasive measurement using current probe, it is working fine.
Anyone knows the reason on why is this happening?
My suspect thoughts:
In the MCP73831 device (I assume MCP73833 also might be having this feature, but it is not mentioned in the datasheet), section 4.2, page 13 of the datasheet, there is a battery detection feature. It works by sending a current out of Vbat pin and measures the battery voltage and indicates whether it is charging or charge complete through the STAT pins. Maybe, is it because, MCP73833 also has this feature and provides some current which interferes with the current measurement in the series multimeter?
Even with the 10A current measurement setting in the multimeter, maybe there's some voltage drop associated with it. This voltage drop reduces the effective voltage seen at the battery terminals and decreases the charging current? Not sure.
Any thoughts on this?