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BQ20Z655-R1: 4MHz Oscillator Status During Sleep

Antonio Fadhel
Genius 9410 points
Part Number: BQ20Z655-R1

Hi Team,

Can you please comment on the questions below from my customer regarding the bq20z655-R1 oscillator?:

In the bq20z655-R1, there is a high frequency oscillator (4MHz) and a low frequency oscillator (32kHz). My understanding is when the bq20z655-R1 enters “Sleep Mode”, it runs off of the 32 kHz clock to conserve power. What happens to the 4 MHz oscillator during “Sleep”? Is it supposed to turn off or does it just idle?

Thanks,

Antonio

bq20z655-R1

  • 0
    TI__Mastermind 42535 points
    Hi Antonio,

    It turns off during sleep.
  • 0 in reply to Batt
    Prodigy 20 points

    The reason behind the original question is due to the results of a radiated emissions test. During the test, in the 50 MHz to 70 MHz band, peaks every 4 MHz were observed. These peaks remained the same whether or not the battery was sleeping. Using a magnetic loop, we were able to see the same 4 MHz peaks emanating directly from the bq20z655-R1.  Again they remained the same whether or not the battery was sleeping. This led us to believe that maybe the 32kHz oscillator and the 4 MHz oscillator didn't actually turn off, but were switched in and out so the microprocessor would consume less power. Obviously, this contradicts the previous answer. How can we verify that the 4 MHz oscillator does in fact turn off?

  • 0 in reply to Richard Cecchini
    TI__Mastermind 42535 points
    The easiest way to do that is to measure power consumption. If your smbus lines are floating and there's no comms and no current to the gauge it will enter sleep mode. Once in sleep mode you supply current should drop to 124uA or less.
  • 0 in reply to Batt
    Prodigy 20 points
    Yes. We are monitoring the power consumption and the spectrum at the same time. We observe the power consumption drop from active mode to sleep mode, but the spectrum stays the same.
  • 0 in reply to Richard Cecchini
    TI__Mastermind 42535 points
    OK. There's no way you can get power that low consistently if the gauge is not in sleep mode. In any case I'll talk to our systems engineers and confirm what I mentioned here.
  • 0 in reply to Batt
    TI__Mastermind 42535 points
    I confirm what I said yesterday. When in sleep the HFO is off, we only wake it up to to ADC (5s) or ADC+CC (20s) measurements controlled by fw.