• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 20 subscribers
  • Views 936 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

bq32000: RTC battery life

user5087263
Intellectual 390 points
Part Number: BQ32000

Hi,

What is the formula used to calculate the RTC coin cell battery life?

As customer requires this information, Can I know how to calculate?

Regards,

Bhavishya AJ

  • 0
    TI__Genius 16845 points
    Hi Bhavishya,

    You can estimate the battery life by dividing the battery capacity by the BQ32000 backup supply current.

    For example, let's use 250mAh coin cell battery. From Figure 2 in the datasheet we can determine the I_back when VCC = 2V. When V_back = 3.0V, I_back is about 90uA. This gives a battery life of approximately 250mAh / 90uA = 2777.778 hours = 115.74 days.

    Kind regards,
    Lane
  • 0 in reply to Lane Boyd
    Intellectual 390 points

    Hi,

    Thanks for the reply.

    But Iback is typically 1.2uA from datasheet and when we measured we found it to be 1uA.

    VCC=3.3V

    V-back=3V

    Capacity of RTC coin cell battery 220mAh

    As per your calculation it should be

    220mAh/1.5u =146666.67 hours which is 16 years.

    The coin cell battery used is maxwell CR2032 which is unrealistic with 16 years. 

    can you suggest any other method to find the life time of battery?

    Regards,

    Bhavishya AJ

  • 0 in reply to user5087263
    TI__Genius 16845 points
    Hi Bhavishya,

    This is a standard method for estimating battery life. You can multiply by a factor of 0.7 for your design constraint: www.digikey.com/.../conversion-calculator-battery-life.

    When VCC = 3.3V and Vback = 3V: Vback will not be used and VCC will be used. This gives 0.7*16years = 11.2 years battery life while the backup supply is not being used.

    Finally, the Iback value given in the datasheet is given under specific measurement conditions. I recommend to measure Iback in your application when calculating battery life.

    Kind regards,
    Lane Boyd