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BQ34Z100-G1: Power down during shutdown, CE Pin behavior

Lukas Simon
Prodigy 110 points
Part Number: BQ34Z100-G1
Other Parts Discussed in Thread: BQ76942, , TIDA-010030, BQ34Z100, BQ34Z110, BQ34110

I have some questions regarding the BQ34Z100-G1 device in combination with a BQ76942 monitor:

I have a setup where i want to combine the BQ76942 Monitor with BQ34Z100-g1 as top of stack fuel gauge. Everything should work in stand alone(Monitor programmed via OTP) and i want just to read from the battery pack. The questions are about how I can reduce power consumption in shutdown mode and whether this is also permissible with the fuel gauge. The monitor can be placed in a shutdown mode where it consumes approximately 1µA of current. Unfortunately, the lowest current consumption of the fuel gauge is approx. 30µA in fullsleep. 

Question 1: 

Is it OK to disable the fuel gauge when the monitor is in shutdown mode? I think I read once that the fuel gauge should always be connected to the battery because it takes measurements from time to time. In the reference design TIDA-010030, the fuel gauge is deactivated and the power supply is switched off when the monitor is in shutdown or shipping mode. Is this a good and approved approach? Or should the fuel gauge always be connected? I think that would drain a smaller buttery pack over time

Question 2:

Unfortunately, the data sheet does not contain much information about the CE pin of the fuel gauge. Its also hard to test because the EVM does not expose that pin separately. Could this pin be used (if question one allows) to deactivate the fuel gauge and thus reduce power consumption when the monitor is in a shutdown state? How high is the quiescent current of the pin and are there voltage levels that result in a low or high state available? I could not find it in the datasheet? (I Think about to drive this pin via a GPIO from the monitor because the data sheet mentions a possible GPIO usage: Can be configured for an active-high output to be driven from the REG18 LDO)

Thank you for your help in advance

 

 

  • 0
    Prodigy 110 points

    I would like to kindly ask if an TI engineer can please answer this question? We need this information for design decisions

  • 0 in reply to Lukas Simon
    TI__Mastermind 26580 points

    Hi Lukas,

    Sorry for the delay.

    1. Yes, it is ok to disable the gauge when it is in shutdown. The bq34z100 is a flash gauge, meaning that the memory will be saved even without power. However, the gauge will not have historical data during shutdown periods.

    2. The Chip Enable pin is able to enter shutdown with a low state entered. The bq34z100 shares the same hardware as the bq34z110 where the shutdown current is specified and is the same as for the bq34z100 seen below, and involves the quiescent current.

    I am unclear on what you mean about the voltage levels for this device. I believe they should follow the same values as stated in the data sheet below:

    Regards,

    Anthony Baldino

  • 0 in reply to Anthony
    Prodigy 110 points

    Thank you for the answer so far. 

    A small addition to the questions: There may be more detailed information available:

    Question 1:

    How does this affect the state of charge accuracy when the fuel gauge is woken up from shutdown and then directly measures a higher voltage on the battery because a charger is connected? Does then the SOC jump? Because i assume that my system will be woken up from shutdown by a charger attach. 

    Question 2:

    Yes, I meant the voltage thresholds on the CE pin that results in the LDO activated or disabled. As I can see these were not included in the data sheet of the fuel gauge. These are listed in the data sheet of the BQ34110, but they do not match the measurements that I made on the BQ34Z100. Maybe you have some additional information here. 

    Regards

    Lukas

  • 0 in reply to Lukas Simon
    TI__Mastermind 26580 points

    Hi Lukas,

    1. When the gauge is woken up from shutdown, the initial measurements taken for SOC will be reliant on the measurements taken before shutdown, so if there is a large enough difference in voltage there is a possibility of an SOC jump. However, the gauge will eventually self correct.

    2. Can you please tell me more about the process you received the measurements? This will allow us to look more into this issue.

    Regards,

    Anthony Baldino

  • 0 in reply to Anthony
    Prodigy 110 points

    Hello Anthony,

    I simply made the CE pin accessible with a small cable which I soldered to the pin. Then I checked at what voltage at the CE pin the internal LDO is activated and provides 2.5v in order to find out the voltage thresholds for the CE pin. I don't remember exactly where the voltage levels were for LDO on or off. I think for on it was about 1.46V and for shutdown it was about 1.2V. I remember that I could detect a hysteresis.

  • 0 in reply to Lukas Simon
    TI__Mastermind 26580 points

    Hi Lukas,

    We are currently looking into this, we will have a response by tomorrow regarding this issue.

    Regards,

    Anthony Baldino

  • 0 in reply to Anthony
    TI__Mastermind 26580 points

    Hi Lukas,

    I have reached out to one of our hardware designers of this device to see if he has any insight to this issue. I should have a response for you by the end of Monday.

    Regards,

    Anthony Baldino