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BQ76952: BQ76952 LFO

Jiatu Li
Prodigy 120 points
Part Number: BQ76952


TI experts,

I need DEEPSLEEP mode in my battery pack, I notice BQ76952 can configure LFO in DEEPSLEEP mode. However, I didn't understand this LFO function? It said "allows for a faster responsiveness to communications and transition back to NORMAL mode"

Could you please illustrate what's the benefits if LFO enable in DEEPSLEEP? 

  • 0
    TI__Guru* 81035 points

    Hi Jiatu,

    One example is when SPI communication is used. If you see the SPI section of the BQ769x2 Software Development Guide, it shows that the first transaction will return 0xFF when the LFO is first starting up, so the first transaction must be repeated. By keeping the LFO on, the additional transaction is not needed.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 120 points

    Hi Matt,

    Thanks for your guidance. I see description about "HFO" in BQ76952 technical reference manual page 76, as below

    "In DEEPSLEEP mode, the HFO will take ≈ 4.5 ms to stabilize and be available. This delay means that requested data generally cannot be provided back to the host during the first SPI transaction when the HFO was initially off', "Thus, in cases when the HFO is likely initially off, it is recommended that the host first
    write a "dummy" SPI transaction to waken the HFO, then wait at least 4.5 ms in DEEPSLEEP mode, before sending the intended SPI transaction."

    Regarding to your comments and LFO short description in BQ76952 technical reference manual, the enabled LFO can help SPI redyce ONE transaction? Am I understanding right? I think this is good for SPI responsiveness!

    Besides, what else may LFO influence? Do we have more specific guidance document or application note about it?

  • 0 in reply to Matt Sunna
    Prodigy 120 points

    Hi Matt,

    I also see a typo in BQ769X2 software development guide, in page 14, it said

    "0XF6 is CRC8 of [0xF0, 0xF6]"

    It should be "0XF6 is CRC8 of [0xF0, 0xE7]" ,right?

  • 0 in reply to Jiatu Li
    TI__Guru* 81035 points

    Hi Jiatu,

    I think this is the only advantage of using this bit (reducing first SPI transaction by one cycle). There is still a significant amount of time from exiting DEEPSLEEP mode to the FETs enabling (see section 13.4 in the datasheet). 

    Best regards,

    Matt