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BQ24105 TS pin and NTC

rnutocio
Prodigy 80 points
Other Parts Discussed in Thread: BQ24105

Hi all,

I have been working with BQ24105 and i have connected to the TS pin a thermistor NTC 103AT (the same reported to datasheet and EVM). I have designed the network RT1, RT2 in order to get a temperature range from 0 to 45C using the formulas treported at page 14 of datasheet and I have got RT1 9.31K and RT2442K (the same of datasheet)  but I got a completly different temperature range. The effective temperature range is 20 to 90C. The voltage on VTSB pin is 3.15V. Can you give me some ideas?

Thanks a lot

  • 0
    TI__Guru 56650 points

    The RT1 and RT2 values are correct. Do you have the EVM?

    Would you help me measue the TS pin voltage when the bq24105 charger trigers the temperature fault?

     

  • 0 in reply to Wang5577
    Prodigy 80 points

    Hi,

    we have verified TS and Vtbs pin. Even when the charger is not loaded, we noticed aome high voltage spikes on Vtbs pin. 3.15V with spikes of 300-400mV. Such condition propagates on Vt pin and for this reason I think the charer is not working properly since the voltage on Vt pin is not stable. We have added a 10nF capacitor in parallel to the NTC and in this way the temperature range is correct. What do you think about this? Is there any reason for this behaviour? do you think this is the correct way to follow? Finally, if this is normal for the charger, why is not written on datasheet and in any other AN at all?

    Thanks

  • 0 in reply to rnutocio
    TI__Guru 56650 points

    bq241xx has been released for long time. This is my first time hearing this issue. Does the circuit have a capacitor between VTSB and Vss?

  • 0 in reply to Wang5577
    Prodigy 80 points

    Yes. We connected 0.1uF has described on datasheet.

     

  • 0 in reply to rnutocio
    TI__Guru 56650 points

    Would you share the schematic and layout file to me? I want to study the layout and may find the root cause of 300~400mV noise on VTSB pin.

    Thanks,

  • 0 in reply to Wang5577
    Prodigy 80 points

    Hi, I have fixed the problem. It seems to be connected to the AC-DC power supplier used. I noticed some high frequency noise at vin that seems to make the internal regulator of the BQ24105 instable. Due to that noise the BQ24105 internal regulator used to create VTSB from VIN seme to became instable. I have put a 10pF capacitor from VIN and ground and the problem was solved.

    Thanks