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BQ40Z50 SLEEP MODES

Kamal Najmi
Expert 3435 points
Other Parts Discussed in Thread: BQ40Z50

hi team,

my customer  want to use the Li-Ion Battery Pack Manager chip BQ40Z50 for our battery solution.

 In our use case we discharge the battery with only a few µA current (typical 20…50 µA, max. 200 µA) for a longer time. While this time the BQ40Z50 shall be in Sleep Mode because the consumption in Normal Mode is too much for battery lifetime.

In the datasheet (chapter Supply Current) there are given two Sleep Modes, one with “DSG on” and one with “DSG off”. We cannot use the Sleep Mode with “DSG off” because our device must be powered always with minimum a few µA current. So we only can use the Sleep Mode with “DSG on”.

 Is it possible to use the BQ40Z50 for this use case? We must be sure that the battery can be discharge with a so low current and the BQ40Z50 must not enter the Sleep Mode with “DSG off” in this case. How the chip differ between the two Sleep Modes? Is it possible to disable the Sleep Mode with “DSG off” so that only the Sleep Mode with “DSG on” is available?

regards,

Kamal

  • 0
    TI__Guru 73830 points
    Kamal,
    The DSG FET can remain on in Sleep mode, if the NR bit is set to 1. It can also remain on, if NR = 0 and the IN_SYSTEM_SLEEP bit is set to 1. It sound like you have a non-removable pack, so the NR bit should be set to 1.

    Tom
  • 0 in reply to ThomasCosby
    TI__Expert 3435 points
    thank you for your quick feedback.
    Yes we have a non-removal pack because the BQ chip should be integrated in the battery pack.
    Ok, that means that the battery can be discharged with a very low current (20..50 µA) during the sleep mode and the DSG FET is not switched off if the NR bit is set to 1 (or the IN_SYSTEM_SLEEP bit). Is this correct?
    Can we assume a supply current for the BQ40Z50 of 75 µA for this case?
  • 0 in reply to Kamal Najmi
    TI__Guru 73830 points

    That should be correct.

  • 0 in reply to ThomasCosby
    Prodigy 170 points

    Please correct me if I'm wrong:

    I have discovered that if NR = 1 you -must- leave PRES/SHUTDOWN pin floating. If you leave it tied low you will bypass sleep mode and enter shutdown mode.

    In fact, I haven't found a way to sleep at all with PRES/SHUTDOWN low and NR=1, it's either Normal mode or Shutdown.

    This is kind of important as the datasheet implies that the PRES/SHUTDOWN pin is ignored if NR = 1. Tech reference 5.2.1.1:  "If the [NR] bit is set, the PRES input is ignored and can be left floating."

  • 0 in reply to Adrian Bolden
    TI__Expert 6575 points
    Hi Adrian,
    I have just been testing this, and it looks like on my EVM, I am able to put the part to sleep even though my PRES pin is shorted to ground. How ever I do have to make sure that the SMBC/SMBD are low. Otherwise I have to set the [IN_SYSTEM_SLEEP] bit in the "DA Configuration" to 1.
    Regards,
    Swami