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BQ2000: Vcc=0V condition

tateo yamashiro
Guru 10890 points
Part Number: BQ2000


Hi,

We got a question from the customer about bq2000.
Could you help us?

[Question]
Our customer is considering using bq2000 to attached schematic. In this case, when DC input is absent, BAT and TS pin voltage exist.
According to user's guide of bq2000EVM, this recommends to apply DC input after attaching battery. Therefore we assume BAT pin is ok to use on this usage. But we can't figure whether TS pin is ok or not. So please give us your feedback about below questions.

bq2000 Schematic.pptx

- Are there any concerns on this usage?
- According to datasheet, the absolute maximum rating on any pin is Vcc. Should we avoid to apply any voltage on any pins under the Vcc=0V condition?

Best Regards,
tateo

  • 0
    TI__Expert 8130 points
    Hi Tateo,

    Avoid setting any pin under Vcc = 0V. Vcc is used as a source for two of the safety functions. For instance, setting the maximum charge time and temperature monitoring configuration.
    In the attached schematic, the output of the LDO is used as a source for the voltage divider network on TS pin. Is there a specific reason for that? Setting the resistor network like Figure 6 in the datasheet would be more beneficial as having RT2 in parallel with R_NTC would allow for lower and upper temperature thresholds.
    Be sure that BAT and TS pin fall under the correct voltage range for the charger to function properly. (V_LBAT < VBAT < V_MCV and V_HTF < VTS < VLTF)

    Regards,
    Alejandro
  • 0 in reply to iAlejandro
    Guru 10890 points

    Hi, Thank you for your reply.

    NiMH is built in thier application. So, at least, the BAT pin voltage exists under Vcc=0V condition. We assume it is ok for this usage, because setup procedure in user's guide of EVM recommends to connect the charge supply after connecting the battery. Is this our understnading correct?

    Regarding to TS pin, they want to monitor the NTC by bq2000 and MCU. While DC input is absent, NTC voltage should be applyed through LDO. This is why they need LDO. But I think I can discuss to them whether they can change the schematic or not.

    Best Regards,
    tateo

  • 0 in reply to tateo yamashiro
    TI__Expert 8130 points

    The set up procedure you are referring to in the User's Guide is how to set up the EVM when charging a battery pack.The BQ2000 is for fast-charge management and provides safety features for battery charging only.

    When an input supply is present, then the IC can monitor the NTC through the TS pin and battery voltage on BAT pin.
    When a DC input is absent, then the IC would not have functioning battery voltage/temperature monitoring circuits. Therefore, they would have to monitor through the MCU.

  • 0 in reply to iAlejandro
    Guru 10890 points

    Hi, Thank you for your support. I discussed to the customer and they will change the schematic to that the voltage of TS pin doesn't exist under the Vcc=0V condition.

    So please let me confirm about this usage. When DC voltage is absent and the IC isn't expected functional behavior, is it ok to apply the voltage on BAT pin?

    Best Regards,
    tateo

  • 0 in reply to tateo yamashiro
    TI__Expert 8130 points
    As mentioned above, if the DC input is absent then the IC would not have a function battery voltage monitoring circuit. Therefore, applying voltage on BAT pin should not be a problem. Recall that the absolute maximum voltage rating on any pin is Vcc.
    Also, make sure that the voltage at BAT pin when IC is operating (input supply is present) falls within range, V_LBAT < VBAT < V_MCV, for proper charging behavior.