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TPS65981: Using VDDIO at 1.8V

David McCoy
Prodigy 155 points
Part Number: TPS65981

I would like to interface with the TPS65981 with an I2C bus running at 1.8V.

I understand that I will need to supply VDDIO with 1.8V and configure the chip through the SPI flash to actually use VDDIO.

I am concerned with power supply sequencing. My board will be a power sink and a data source (Think of a laptop without a battery). The board will not power up with anything less than 9V so I will not be able to enable the main regulators on the board until the TPS65981 can negotiate an appropriate voltage. I would like to have an I2C communication channel between the TPS65981 and the main processor but the processor's I2C bus runs at 1.8V and I don't want to expose that I2C bus to 3.3V.

I can connect LDO_3V3 to VDDIO to have 3.3V on the I2C but how can I supply the VDDIO with 1.8V if I can't power up my main regulators.

Would it be okay if I attach a 1.8V LDO to LDO_3V3?

Can I use LDO_1V8D?

I plan on supplying VIN_3V3 with an external 3.3V once the main regulators are up and running.

Thanks for any help,

Dave

  • 0
    TI__Genius 12990 points

    Hi Dave,

    you can buck down LDO_3V3 to get 1.8V for the I2C bus. The external loading capability of LDO_3V3 is 30mA as opposed to the LDO_1V8D of 5mA (which may or may not be enough). This info can be found in the electrical characteristics of the datasheet. There are also I2C characteristics.

    the x981 can be either powered by VBUS or VIN_3V3 => At power-up, when VIN_3V3 is not present a dead-battery condition exists.

    according to the datasheet: VDDIO may power-up before LDO_3V3. When VDDIO powers up before LDO_3V3, the I/Os shall not be driven high. When VDDIO is low and LDO_3V3 is high, the I/Os may be driven high.

    Let me know how I can further help.

    Thanks