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BQ76930: BQ76930 TS1 Pin has been placed a 4700pF Cap

Rock Su
Intellectual 2220 points
Part Number: BQ76930

Dear Colleague,

Our customer is a using BQ76930 for 6S battery pack. Now they don't use the TS1 to sense Temp, but they reserve the NTC and Cap paralleled with NTC position in the layout.  

So they find when they only placed a 4700pF Cap in TS1 pin, in low temperature(<-10℃), can't start up consistently, the second boot is about 20 seconds from the first boot. When in the normal temperature, this didn't happen.

In my opinion, the low temperature could change the cap value, between the first and second boot, Vcap has less change. So BQ76930 can't catch the high boot voltage.

When customer uses oscilloscope and multimeter to test, always work properly.

But we can't find the BQ76930 internal circuit in the datasheet, so could you please help us analyze this problem?

Thanks a lot!

B.R

Rock Su

  • 0
    TI__Guru 54715 points
    Hi Rock,
    The TSn pins must have pull downs for the part to start up properly. Normally the thermistor provides a pull down. The cap is not required, it is suggested as an option to stabilize the voltage from the thermistor for during the temperature sample.
    Without a pull down and with a cap the time constant of the net must be longer when cold. A scope probe or meter would provide a load and pull down the net.
    If they are not measuring temperature they would not need the cap for stability of the measurement. If the boot circuit does not have transients they would not need the cap for transient protection. They may consider removing the cap, but the pin should still have a pull down resistor.