Hi,
I received back a PCB which has an issue regarding the battery. It happens only on one battery (plus another I had in the lab) and it's confusing me. The MAX17055 chip is implemented on the PCB to send the level and the state of charge of the battery. I did several test with the pcb and the battery in question (DEVICE1, BAT1) and another pcb and another battery that are good (DEVICE2, BAT2) :
With DEVICE1 and BAT1 I measure a low value on the pin /ALRT, correct values on the I2C communication (SOC 78% and Voltage 4.081V) and a correct value on the battery with my voltmeter (4.081V).
With DEVICE1 and BAT2 I measure a high value on the pin /ALRT, correct values of the battery.
With DEVICE2 and BAT1 I measure a high value on the pin /ALRT, correct values of the battery.
So it's only the combinaison of the the first device/battery that goes wrong which doesn't make any sense to me.
Coming back to DEVICE1 and BAT1 : I read the Status register (00h) to have more info on what triggers the alert.
I receive the value 0x0482. 0x0082 is dSOCi and POR bits so whatever.
But 0x04 is the Smn bit which indicates if the threshold of the minimal limit (RepSOC) has been crossed.
"Smn and Smn (Minimum/Maximum SOC Alert Threshold Exceeded): These bits set to a 1 whenever SOC is below (Smn) or above (Smx) the SAlrtTh thresholds." (The error in red is in the user guide and not in the datasheet but it's not important)
So the chip triggers an alert that says the state of charge is below the limit but at the same it measures a perfectly correct value of the battery ?
Note that the threshold is set to 1% or 5% or 2.5V or 2.8V in the code I have (didn't have time yet to properly read the code but it's not a firmware issue), so anyway a value that is way below the measurement of 78% or 4.081V.
Do you have any idea of what is going on or some details on the threshold/measurement of the battery by the MAX17055 ?
Also I saw that in the datasheet (not in the user guide) -> "Interrupts are generated on the ALRT pin open-drain output driver. An external pullup is required to generate a logic-high signal."
There isn't a pullup resistor on the /ALRT line on the schematics I have. Could it be an issue, is this pullup really necessary ? Though it's not the current issue I have since the Status register gives the info of the Smn bit.
This issue only appears currently on two batteries, I could have had a few ( < 5) boards that had this problem in the past on hundreds of them.
Thanks in advance !
Best,