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BQ2000: Discharge current

May
Genius 9880 points
Part Number: BQ2000


Hi,

Customer is currently have a question about a bq2000sn-b5 chip, please see details below.

Customer currently using to recharge a NiMH battery pack of 13 cells of their product. The BAT+ connector connected to a voltage divider of 230k and 18k, where the voltage across the 18kOhm goes to the BAT pin (after being filtered by and RC of 100kOhm and 100nF as suggested in the datasheet. The current sensing resistor is set to 0.33 Ohm, to charge at 150 mA. Everything works good, but recently they are stocked their product for 6 months and some batteries went down to half capacity.

Since the BAT+ goes to earth by the resistors of 230k and 18k, they calculated a battery discharge of 65 uA. At same time, noticed that they have another voltage divider in their project (that goes to an ADC) and it uses a 100k and 15k resistors, hence a discharge current of 130 uA.

Customer wanted to know if there are any good suggestions to reduce these currents during storage. Maybe increasing the resistor values? Something different? 

Thank you in advance.

Regards,
Maynard

  • 0
    TI__Mastermind 41485 points

    Dear Maynard,

    The maximum recommended input voltage for VCC is 6 V. This is a buck charger, so are you positive the battery back was fully charged? In fact the maximum charge voltage listed on the product page is 6 V.

    The sum of the resistor divider must be at least 200 kOhm and no more than 1 MegaOhm.

    Thanks,

    Mike Emanuel

    Please click "Resolved" if this answered your question.

  • 0 in reply to Michael Emanuel35
    TI__Genius 9880 points

    Hi Mike,

    I just received response from customer, please see details below.

    The VCC pin is set to 5V as specified in the datasheet. The resistor divider sum is 248 kOhm , but this line can discharge some amount of current to ground. We have another line which can discharge, as previously specified. The battery were stored fully charged, so I was wondering if increasing the resistor values is the only way to reduce this effect.

    Regards,
    Maynard

  • 0 in reply to May
    TI__Mastermind 41485 points

    Dear Maynard,

    As outlined earlier, the sum of the BAT pin resistor divider is at least 200 kOhm and no more than 1 MegaOhm. Therefore, they could increase the values such that the total is less than 1 MegaOhm.

    What are they using the ADC for?

    Thanks,

    Mike Emanuel

    Please click "Resolved" if this answered your question.

  • 0 in reply to Michael Emanuel35
    TI__Genius 9880 points

    Hi Mike,

    Just receive response from customer, details below.

    "Is there other solutions other than increasing the resistance that you can recommend. The ADC is used to read the battery voltage on a micro."

    Thank you in advance.

    Regards,
    Maynard

  • 0 in reply to May
    TI__Mastermind 41485 points

    Dear Maynard,

    Can you please confirm the desired charge voltage (you mentioned 13 cells earlier)? The maximum charge voltage listed on the product page is 6 V.

    Thanks,

    Mike Emanuel

    Please click "Resolved" if this answered your question.