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BQ32000: power the RTC from main battery

Gonzalo Sanchez1
Prodigy 70 points
Part Number: BQ32000
Other Parts Discussed in Thread: BQ24295,

Hi everyone, 

We are working on a new portable device that required an RTC and that will be powered by a non-removable rechargeable Li-On battery of 3.7v 3000mAh. The bq24295 will be used as power management and the tps63025 as the battery to 3v3 regulator. My question is, may I used the main Li-On battery as Vbat for the RTC instead of a coin battery? We would like to avoid using a coin battery due to many import and export restrictions on many countries of the products which contain these types of batteries. A supercapacitor is not an option since the device may be powered off for long periods of time.

I was thinking to connect the RTC Vcc to the 3v3 regulated voltage (from the tps24295) and the RTC Vbat somehow to the main battery (Vbat from bq24295). The problem with this is that the main battery voltage range between 3v and 4.2, which is higher than the Vcc 3v3.

Any suggestion you about this problem?

Regards.

  • 0
    TI__Genius 16845 points

    It is OK to supply from the Li-ion battery. Did you intend to use the integrated trickle charger of BQ32000 to recharge the battery? In that case, you must adhere to battery charging guidelines in the battery datasheet.

    There is no issue in having VCC and Vback connected simultaneously. Internal switchover from VCC to VBAT occurs when VCC drops below ~2.8V as detailed in section 7.3.2.

    Kind regards,
    Lane

  • 0 in reply to Lane Boyd
    Prodigy 70 points

    Hi Lane, thank you for your help.

    The problem is that the battery voltage can be higher than the 3v3 regulated Vcc and the datasheet state that Vback <= Vcc. But I imagine I can use a low Iq linear regulator between the battery and the Vback RTC input.

    Regards,

    Gonzalo.

  • 0 in reply to Gonzalo Sanchez1
    TI__Genius 16845 points

    Hi Gonzalo,

    My apologies, I forgot to comment on that. I agree, a low Iq LDO will solve it

    Kind regards,
    Lane