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BQ25176J: Issue with TS Pin Current and Thermistor Capacitive Load on BQ25176EVM

shinsuke sato
Prodigy 10 points

Part Number: BQ25176J
Other Parts Discussed in Thread: BQ25176, , BQ25170

Tool/software:

Hello,

I’m evaluating a battery with a thermistor connected to the BQ25176EVM board.

However, when the thermistor-equipped battery is connected, the PG LED begins blinking, and it appears that the constant current (38 µA) is no longer being supplied from the TS pin.

Upon inspecting the battery, I found that there seems to be a capacitor of approximately 0.1 µF connected in parallel with the thermistor.

Does the BQ25176 include any kind of timeout behavior where, if the TS pin voltage doesn’t settle within a specified range within a certain time, the current source is disabled?

If so, could you clarify what that timeout duration and the expected voltage threshold (perhaps V_TS_EN?) would be?

Any insights would be greatly appreciated.

Best regards,

  • 0
    TI__Guru* 78396 points

    Hello

    shinsuke sato said:
    when the thermistor-equipped battery is connected, the PG LED begins blinking,

    This is an indication of a fault condition, probably TS HOT or TS COLD.   

    When connecting the battery pack Thermistor to EVM -- Removed JP6 Shorting Jumper (needs to be OPEN).

    What is battery pack Thermistor value?

  • 0 in reply to Bill Johns
    Prodigy 10 points

    Hello,

    Thank you for your response.

    The JP6 shorting jumper is not installed and is left open as required. As for the battery pack thermistor, I measured its resistance with a multimeter and it is approximately 8.5 kΩ at room temperature.

    Best regards,

  • 0 in reply to shinsuke sato
    Prodigy 10 points

    Additionally, I confirmed with the battery manufacturer that a 0.1 µF capacitor is indeed connected in parallel with the thermistor.

    Best regards,

  • 0 in reply to shinsuke sato
    TI__Guru* 78396 points

    Hello

    shinsuke sato said:
    I confirmed with the battery manufacturer that a 0.1 µF capacitor is indeed connected in parallel with the thermistor.

    I have tested with a 0.1uF in parallel with NTC on EVM an found that unit will not start correctly.  The additional load on TS will trip Charge Disable, 75mV.

    You should see a short pulse on PG every 2 sec.

  • 0 in reply to Bill Johns
    Prodigy 10 points

    Hello,

    Thank you for your confirmation. Just to clarify—does this mean that temperature monitoring with the BQ25176J may not function correctly when a 0.1 µF capacitor is connected in parallel with the thermistor in the battery pack? If there are any effective countermeasures or recommended workarounds for this condition, I would greatly appreciate your guidance.

    Best regards,

  • 0 in reply to shinsuke sato
    TI__Guru* 78396 points

    What charge temp range do you need for battery?

    A series resistor may help but will change the temp trip points.  See BQ25170 TS Pin Section 7.3.2.4.

    The standard BQ25176J:

    Hot-55C (off)

    Warm-45C (Ichg to 50%)

    Cool-10C (Ichg to 20%)

    Cold-0C (off)

  • 0 in reply to Bill Johns
    Prodigy 10 points

    Hello,

    Thank you for the information. As mentioned in the datasheet, adding resistors does seem to be an effective approach. We would like to enable charging within a temperature range of 0 °C to 40 °C. Would it be possible for you to provide the formulas or method to calculate Rs and Rp based on this desired range?

    As an initial trial, we considered inserting a 2 kΩ resistor in series with the thermistor. This appears to allow us to meet the VTS_EN = 75 mV threshold with the 38 µA current source. However, this may undesirably raise the high-temperature shutdown point, so we would prefer a more appropriate solution if available.

    Best regards,

  • 0 in reply to shinsuke sato
    TI__Guru* 78396 points

    Hello

    Thanks for the update.

    I have run calculation with 2k series resistor, and it is difficult to reduce the Hot temp.

    Checking on other options.

  • 0 in reply to Bill Johns
    Prodigy 10 points

    Hello, Thank you for investigating this further. I appreciate your continued support and look forward to any alternative approaches you may be able to recommend based on your analysis.

    Best regards,

  • 0 in reply to shinsuke sato
    TI__Guru* 78396 points

    Hi 

    Do you have any information on the battery pack NTC?  

    Is an MCU available to send a reset pulse to an external circuit?

    Below are some calculations on the temp range vs Rs.

    Rs - ohm 0 500 1000 1500 2000
    Cold 0 0 1 2 3
    Cool 10 10 10 12 12
    Warm 45 48 48 55 60
    Hot 55 60 65 71 80
  • 0 in reply to Bill Johns
    Prodigy 10 points

    Thank you for the information.

    The battery pack contains an NTC thermistor model TN11-3H103JT-NTC10K, and its characteristics are described in the following PDF: www.mmc.co.jp/.../TN11-3H103J.pdf

    Additionally, since charging is handled in a standalone configuration, no external MCU is available.

    We will review the information you provided and explore possible solutions based on it.

    Best regards,