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BQ76952: Supply voltage REG1 pin

Maarten Hermens
Prodigy 30 points
Part Number: BQ76952

Tool/software:

We only have a 3.3 V supply available and would prefer not to generate a 5.5 V supply for the REGIN pin of the BQ76952.

Our MCU runs at 3.3 V and communicates with the BQ76952 via SPI. According to the datasheet (section 7.6), the SPI output high level (VOH) is referenced to REG1.

Is it possible to supply REG1 with 3.3 V so that the SPI interface operates at 3.3 V logic levels? 

  • 0
    Intellectual 486 points

    Hello Maarten,

    BQ769x2 has a BREG pin which can be used to drive an external preregulator transistor to generate this 5.5V supply for the REGIN pin from your BAT+ voltage. Please check the the reference designs or typical application schematic present in the datasheet.

    Maarten Hermens said:
    Is it possible to supply REG1 with 3.3 V so that the SPI interface operates at 3.3 V logic levels?

    REG1 and REG2 are OUTPUT pins which can be programmed to various voltage levels. This not an INPUT supply pin to the AFE. From section 8.1 of the datasheet: Dual programmable LDOs are included for external system use, with each independently programmable to voltages of 1.8 V, 2.5 V, 3.0 V, 3.3 V, and 5.0 V, capable of providing up to 45 mA each.


    So with the recommended circuit for the REGIN/BREG, all you have to do is program the REG1 LDO output to 3.3V for your SPI lines to be referenced to this voltage level.

    Best,
    Abhijith

  • 0 in reply to Abhijith V Narayan
    Prodigy 30 points

    Hello Abhijith,

    Thank you for your support.

    From the datasheet, I understand that the input pins of the BQ are 5V tolerant. I plan to drive CS, MOSI, and SCLK with 3.3V MCU levels, while using a level shifter for the 1.8V MISO signal. Could you please confirm if this approach is correct?

    Additionally, can you confirm whether REG18 is not supplied from the REGIN input? In our design, I intend to leave both BREG and REGIN unused.

     

  • 0 in reply to Maarten Hermens
    Intellectual 486 points

    Hi Maarten,

    I am not sure if this would be okay. The V(OL) level when these pins are supplied using REG18 is not available in the datasheet, I think. So TI engineers ( ) would have to confirm this. I think the more appropriate option would be to use a 4 channel level shifter for the SPI signals and call it a day.

    Yes, REG18 gets power from BAT pin and not REGIN. So you'll be fine.

  • 0 in reply to Abhijith V Narayan
    TI__Prodigy 740 points

    The VOH will very based on which supply(REG1 vs REG18) is used for the output pull-up driver. 


    However, reviewing the design shows the output pull-down driver is always driven by REG18. 
    So the VOL will always be the same no matter which supply is used for the GPIO output driver.