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TPS40422: PMBus activation timing

TI_pwr_usr
Intellectual 280 points
Part Number: TPS40422

From power up (VDD applied) when is SMBus interface become available to accept master access?

  • 0
    TI__Mastermind 24075 points

    Hello, 

    The time from VDD power up to PMBus internal available is very short. 

    I don't have the exact number, but it should be shorter than 1ms. 

    Thanks

    Qian

  • 0 in reply to Qian Chen
    Intellectual 280 points

    Thanks. As for pullups on the SCL/SDA/SMALERT, because the internal 3.3V regulator capacity is limited, I plan to use external voltage to supply the pullup If the external 3.3V is applied to the pullup before 12V is applied to TPS40422, do you see any issue messing up the internal state machine?

  • 0 in reply to TI_pwr_usr
    TI__Mastermind 24075 points

    Hello, 

    It is fine that external 3.3V voltage (pull-up voltage for SCL/SDA/SMALERT) comes before 12Vin. 

    Thanks

    Qian 

  • 0 in reply to Qian Chen
    Intellectual 280 points

    One last question: I'm not sure how exactly ADDR[1:0] work.

    According to the datasheet, ADDR1 sets the 10s digit while ADDR0 sets the 1s digit. For example, if 127K pull down is on ADDR1, and 38.3K pull down on ADDR0, the I2C slave address would be 63. Is it correct? Is 63 a decimal or hex? Is it 7-bit address or 8-bit addrss?

    Then if you look at the reference design in the datasheet both ADDR1 and ADDR0 are pulled down by 36.5K ohm, which isn't defined by Table 3 on page 26. So what 8-bit hex address does it strap the device to?

    For reference, the 8-bit address means to pad 0 at bit[0]. You know bit[0] is read/write indicator in the I2C protocol. A 7-bit address 7'b1010000 would be equivalent to 8-bit address 8'b10100000.

    Thanks.. 

  • 0 in reply to TI_pwr_usr
    TI__Mastermind 24075 points

    The 7 bit address consist of 0b+ADDR1+ADDR0. Both ADDR1 and ADDR0 are 3bits. 

    For example, if resistor is 38.3k, it means 011b. If resistor is 82.5k, it means 101b. 

    The 8 bit address is 7bit address followed by r/w bit.

    The EVM was released by others many years ago, I have no idea why 36.5k is used. Please refer to datasheet table 3 to select resistor value. 

    Thanks

    Qian