Open Cell fault after assembly

Ran Aloni

Dear all,

I have received my PCB with schematic that was discussed here in the Forum.

I have a repeating issue.

I have a series FET connection method (discharge and charge FET are in series) and a steady 15K resistor between B+ and CHGST.

because of that I cannot power down the PCB by shorting the thermistor.

so when the assembly is done (I try to do it squently but it is a very difficult assembly), I have an "open cell" fault that just do not resets.

what is the right way to do it? what will assure a safe and fast assembly and activation of the pack.

my suggestions:

1) to disconnect the 15K resistor during the assembly and short the thermistor during all through the assembly,

2) disconnect the resistor the will go to BAT pin (R4) during assembly - which means no power to the inner voltage regulator.

needless to say this is extremely extremely urgent.

thanks for the help, schematic attached.

Schematic_B4.pdf

over 12 years ago

0 Ran Aloni over 12 years ago

Expert 2386 points

Dear all,

solution 1 don't work, what works is removing the 15K resistor after writing the right parameter to EEPROM, then returning it.

the thing is I have 8 cells and the default is 10 cells so an open cell fault always appear but does not reset because my 15K resistor.

is there a better way to avoid this problem?

in which cases in normal operation will I have to repeat this action.

the battery and PCM will be closed in ultra sonic!

regards,

0 WM5295 over 12 years ago in reply to Ran Aloni

TI__Guru 54715 points

You could reset the part as described here, http://e2e.ti.com/support/power_management/battery_management/w/design_notes/1450.bq77910-reset-how-can-i-recover-from-a-permanent-fail.aspx but controlling CHGST may be easier. Depending on the power rating of the 15k resistor and the voltage of your cells you may be able to safely short CHGST low momentarily after programming and the open cell fault. CHGST low will allow it to shut down, then remove the short to recover.

0 Ran Aloni over 12 years ago in reply to WM5295

Expert 2386 points

Dear WM5295,

thank you very much,

assembling with a link of CHGst to the GND and removing it after programing solved this issue.

can you answer my question about, in what other conditions, should I expect that a CHGST ground will be the only thing that will wake the battery up?

my problem is lack of access to the pin after assembly.

thanks,

0 WM5295 over 12 years ago in reply to Ran Aloni

TI__Guru 54715 points

CHGST 'high' wakes the device. Fault recovery is summarized in the datasheet table 2. Open wire as you found and SCC require CHGST to go low to recover.

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Open Cell fault after assembly