• State TI Thinks Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 2 answers
  • Subscribers 64 subscribers
  • Views 339 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ76942: the power dissipation of BQ76942

GJ H
Prodigy 140 points
Part Number: BQ76942

Tool/software:

Dear TI experts,

         We have used your company's BQ76942 chip in the battery protection system, but we have encountered a problem and would like to ask for your advice.

         Background of the problem: ①. We used the charge pump driver of BQ76942 and connected the LD pin of the chip to P+ through a resistor; ② The product is subject to photovoltaic charging, and if the input power of the photovoltaic is relatively low, it will not be able to charge the machine; ③ Based on the second point, at this point, the AFE will have a power consumption of about 320uA, which will continue to discharge the battery;④ Our software engineer attempted to put the AFE into deepsleep mode and sent two commands within four seconds according to the specifications, but the AFE did not enter deepsleep mode, as shown in the waveform below.

        We are concerned that in the event of continuous rainy weather, the photovoltaic system may not only fail to charge, but also deplete the battery.

     ① May I ask if there is a way to completely shut down AFE in this situation? ② If shutdown is not possible, can the AFE enter deep sleep mode to minimize power consumption as much as possible? ③ Do you have any good suggestions to reduce power consumption in this situation？The problem is urgent, looking forward to your reply！

  • 0
    Prodigy 140 points

    Additional point: When we connect PV photovoltaic input, there will be a voltage of about 3V at the PACK+ end

  • 0 in reply to GJ H
    TI__Expert 4320 points

    Hello,

    Can you confirm what the pink line the waveform of the first picture represents?

    Best regards,

    Thomas Rainey

  • 0 in reply to Thomas Rainey
    Prodigy 140 points

    the pink line （No.4） represents signal  of RST_SHUT pin, and the green line（No.2） represents 3.3V power supply. In this project, we used software to simulate IIC communication(No.1,No.3)

  • 0 in reply to GJ H
    TI__Expert 4320 points

    Hello,

    The reason the device is not entering DEEPSLEEP MODE may be due to the fluctuating voltage on the LD pin. 

    If the voltage at the LD pin exceeds the VWAKEONLD voltage the device cannot enter DEEPSLEEP MODE.

    This logic also applies to SHUTDOWN MODE:

    In your case the 3V at the PACK+ exceeds the max limit of the VWAKEONLD:

    In order to decrease power consumption you could utilize the SLEEP MODE which can bring the power consumption to between 21µA to 41µA. SLEEP MODE can be configured to not exit when that 3V is applied to PACK+:

    Best regards,

    Thomas Rainey 

  • 0 in reply to Thomas Rainey
    Prodigy 140 points

    Hello,

           When I separate the LD pin from the PACK+, the voltage at the LD pin is 0 V (as shown in the figure), but the AFE BQ76942 still cannot enter shutdown mode. The voltage at the REG1 pin remains at 3.3 V. What is the reason for this? Why can't AFE enter shutdown mode? Do you have any suggestions for this?

          Looking forward to your reply!

  • 0
    Prodigy 140 points

          To add a few more points, ① the circuit related to our TS2 pin is shown in the diagram；② I directly grounded the LD pin through a resistor. 

          I have recaptured the owakeBQ signal controlled by the MCU and the level of TS2 pin. The result is as follows: when the photovoltaic input power is low and the system attempts to shut down the AFE, the shutdown signal (yellow) kept high, while the owakeBQ signal controlled by the MCU (blue) kept low (the 960mV in the diagram is due to the deviation of the oscilloscope I used, which I am sure), but strangely, the TS2 pin is still at a low level.

    Shouldn't TS2 be weakly pulled up without our MCU control? Why is the TS2 pin low in this situation? How should we solve this problem？

          As a reference, the last figure shows the waveform under normal shutdown conditions: the shutdown signal maintains a high level greater than 1 second, the owakeBQ signal remains low, TS2 is weakly pulled up to 3.5 V, AFE enters shutdown mode, and the REG1 level begins to fall.

          Looking forward to your reply!

  • 0 in reply to GJ H
    TI__Genius 17875 points

    Hello GJ H,

    Thank you for your patience and for sharing your labeled waveforms. From the looks of it, you most likely entered the Soft SHUTDOWN state for the device. More information regarding how Soft SHUTDOWN is entered and how to avoid/exit it, can be found in this BQ76952 FAQ Soft SHUTDOWN State. More specifics on the SHUTDOWN mode can also be found in this BQ76952 SHUTDOWN mode FAQ.

    Best Regards,
    Alexis