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Original question:

BQ78350-R1: LCD Blinking Issue

BQ78350-R1: High Current Consumption + LCD Blinking Issue

user5503575
Intellectual 800 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQ76930, , BQ20Z655-R1, BQ78350

Hi,

I have designed a BMS which uses BQ76930 and BQ78350-R1. When I use battery, my LCD blinks irregularly and this situation doesnt change when I disconnect or connect SMBus.

Also my PCB current consumption is approximately 5mA. I desolder LCD and LCD connection resistors, current consumption decreases 0.4mA.

I think there is problem about my LCD driver side but I followed SLUA924 (page 17) schematic. And I use same lcd on my other BMS which uses BQ20z655-R1 without any problem.

Do you have any idea about current consumption and blinking issue? I have to fix that problem. 

  • 0
    TI__Guru* 81034 points

    Hi,

    In the BQ78350-R1 Technical Reference Manual, there is the following paragraph in Chapter 13:

    Liquid crystal displays having an operating voltage range of 2.5 V to 6 V and a refresh frequency between
    30 Hz and 200 Hz are supported. The display refresh must be implemented such that the device current
    consumption requirements during sleep and active modes are not violated. The display refresh frequency
    must always be set as low as the LCD specification allows in order to minimize current consumption.

    There is also an example schematic in the Using the BQ78350-R1 application report.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Intellectual 800 points

    Even I change Lcd frequency, blinking and current issues are keep going.

    I set 35 hertz as default and I designed like TI documents.

    If you want to know the story, The main reason for I measured the board consumption is that my highest cell voltage is not stable. It decrease and increase approximately 150mV.  So I was thinking because the 2.5V regulator needs more power to drive something. Then regulator takes power from highest cell and the highest cell is oscillating.

    Then I measured the IC's consumptions. Bq769x0 needs about nanoamperes if I bypassed regsource needs.) Regulator source pin of Bq769x0 takes 4mA which is too much for me.

    Then I think that the current consumption might related with LCD. I desoldered LCD and measured  currents again. My whole board spends 0.3-0.4mA which is excellent for me. And highest cell is so stable.

    I have different board which uses Bq769x0, Bq78350. It spends similar currents.

    And I have another board which use same Lcd and there is no current consumption issue.

    So please help me about fixing this problem. How can I drive LCD with Bq769x0 and Bq78350 properly?

  • 0 in reply to user5503575
    TI__Guru* 81034 points

    The LCD feature will consume some additional current. I see this older thread that confirms this. I read somewhere that using 4-bar LCD may significantly improve the current consumption, but I do not have a way to verify this at the moment.

    https://e2e.ti.com/support/power-management/f/196/t/382360

    Regards,

    Matt

  • 0 in reply to Matt Sunna
    Intellectual 800 points

    LED's needs current to lighting but LCD almost doesnt need current to show SOC. I really dont understand why my design needs too much current to operate. 

    My battery is almost 3Ah. My board spends 5mA. Even I dont use the battery, my pcb will consume my full cells in 25days. Its really big problem, isnt it?

  • 0 in reply to user5503575
    TI__Guru* 81034 points

    I understand it is an issue. However, the device firmware cannot be changed, so there is no way to adjust the behavior. You may need to try a 4-bar LCD to see if it resolves the issue.