Hi,
I recently purchased a SparkFun LiPo Charger Plus to charge a number of 400mAh sample batteries. One particular set of batteries appear to put the charger in “System Test Mode” (all three leds turned on at the same time)
What is system test mode?
What are the reasons system test mode might trigger when plugging in a 400mAh lipo?
Regards
Matt
Hi Matt.
Here’s how the data sheet defines System Test Mode:
5.1.4.1 System Test (LDO) Mode
The MCP73833/4 can be placed in a system test mode.
In this mode, the MCP73833/4 operates as a low
dropout linear regulator (LDO). The output voltage is
regulated to the factory set voltage regulation option.
The available output current is limitted to the
programmed fast charge current. For stability, the VBAT
output must be bypassed to VSS with a minimum
capacitance of 1 µF for output currents up to 250 mA.
A minimum capacitance of 4.7 µF is required for output
currents above 250 mA.
The system test mode is entered by driving the THERM
input greater than (VDD-100 mV) with no battery
connected to the output. In this mode, the MCP73833/
4 can be used to power the system without a battery
present.
Note 1: ITHERM is disabled during shutdown,
stand-by, and system test modes.
2: A pull-down current source on the
THERM input is active only in stand-by
and system test modes.
3: During system test mode, the PROG
input sets the available output current
limit.
4: System test mode shall be exited by
releasing the THERM input or cycling
input power.
There isn’t a clear explanation why the board goes into system test on that one particular battery, but it would seem that there’s a problem with that battery and you should probably not use it with the LiPo Charger Plus.