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bq40z50 Sleep conditions

TcPaden
Expert 1085 points

I want to put the 40z50 into sleep mode with the CHG FET off and the DSG FET on. I've got the following register settings:
DA Config:      0x1A     SLEEP enabled, IN_SYSTEM_SLEEP enabled, REMOVABLE mode, 3 cells.
FET Options:  0x19     CHG FET off during SLEEP.

I've wired the connector to the battery pack so that when it's connected, PRES is grounded.

With the pack disconnected, I measure about 75 µA from the cells, but when I connect it, the current goes closer to NORMAL mode: 450 µA. It stays this way even after waiting the BUS Timeout time.

What condition is not being met to stay in SLEEP mode?

Thanks.

Tom

  • 0
    TI__Guru 73830 points
    I tested the configuration that you described and the gauge remained in Sleep mode after the PRES pin was pulled low. You can monitor the thermistor pin to see whether the gauge is in Sleep mode. Also, verify that there is no SMBus communication. I can test your specific configuration, if you can attach an srec file.
  • 0 in reply to ThomasCosby
    Expert 1085 points

    I verified that there was no SMB communication. I determined it was in Sleep by the current level: what do you see on the thermistor pin in Normal and Sleep modes?

    srec is attached as a zip.bq40z50_SLEEP_for_TomC.zip

    Thanks.

  • 0 in reply to TcPaden
    TI__Guru 73830 points
    I found the current to drop after the device entered Sleep mode. The thermistor will pulse every 500ms to 750ms when in normal mode and every 10s when in sleep mode with your setup.
  • 0 in reply to ThomasCosby
    Expert 1085 points

    Did you find anything that would explain why it's not staying in Sleep mode after the PRES pin was pulled low?

  • 0 in reply to TcPaden
    TI__Guru 73830 points
    The gauge should go to sleep with the SYSPRES pin pulled high or low, if IN_SYSTEM_SLEEP is set and this is what I see on my EVM with your srec file loaded. Are you sure that there is no SMBus activity that is preventing it from remaining in sleep mode?
  • 0 in reply to ThomasCosby
    Expert 1085 points
    With my pack connected to an EV2300 and PC, I connected an I2C (SMB) monitor just to make sure there was no traffic. I put in a switch to toggle PRES. With PRES open, I measure a current indicative of the Sleep mode. Within 5 seconds of grounding PRES, I measure a current that indicates it's back to Normal mode.
    If I open PRES, wait for it to go to Sleep, then send a (CHEM_ID) command, it goes active immediately, then goes back to Sleep after the Bus Timeout time.

    I will try the other tested PCB assembly next week.
  • 0 in reply to TcPaden
    Expert 1085 points
    I've tested two boards now, with the same result. If PRES is open, everything works after the Bus Timeout: current goes to ~70 µA, CHG FET drive drops to inactive (~5V), and the thermistor signal pulses every 10 to 15 seconds.

    But when PRES is grounded (and no communication has occurred), current stays above Sleep mode (~450 µA), CHG FET stays active (~20.8V), but the thermistor still pulses every 10 seconds! This is true after waiting several times the Bus Timeout value.

    Could you try to reproduce what I've found? Thanks.
  • 0 in reply to TcPaden
    TI__Guru 73830 points
    I checked it again on my EVM with your srec file loaded. I placed a current meter in the ground path to the cells. The current measures about 300uA. I then removed the PRES pin jumper and the current measures about 270uA. I allowed the gauge to go to sleep and the current measures 77uA. I reconnected the PRES pin jumper and the gauge remained in sleep mode with the current measuring 101uA. I do not see the full current values that you reported. I can check your module on the bench, if you want to send one to Dallas.
  • 0 in reply to ThomasCosby
    Expert 1085 points

    Was the drive for the CHG FET active while in Sleep mode? I have SLEEPCHG cleared (FET Options), so the CHG FET should be off during sleep, but it stays on in the two boards I have working.

    Don't think that would explain the difference in current between the EVM and my PCB's.

  • 0 in reply to TcPaden
    TI__Guru 73830 points
    It looks like the SLEEPCHG feature only works when NR=1. The CHG FET will already be off when NR=0.
  • 0 in reply to ThomasCosby
    Expert 1085 points

    I see part of my confusion: with your EVM in Sleep, and the PRES jumper removed, current was 77 uA. Reconnect the PRES jumper and current is 101 uA, but you still consider it in Sleep mode. I was thinking that whenever it is sleeping, the current should be the same, but it's not due to changing the timing for checking the PRES pin, ADC reading voltages & currents, etc.
    At least that's what I assume?


    I got similar values on my EVM too, but I'm not sure what you mean by "The CHG FET will already be off when NR=0."?

    With NR=0 and PRES grounded, the CHG FET drive is still high. The only time it goes low is when PRES jumper is removed.