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Original question:

LMP92066: LMP92066

LMP92066: Getting started with the programing of the IC

Vaishak B
Prodigy 70 points
Part Number: LMP92066


Tool/software:

Hi Erin, 
In my use case, During the PA turn OFF sequence, I want to Make the DAC voltage of DAC0 from -3.7V to -5V. Instead of making the DRVEN0 pin as low to get the output of DAC0 as -5V, Can i write the DAC value for -5V using I2C and get the output of DAC0 as -5V by keeping the DRVEN0 pin as high.
Basically I don't want to make the DRVEN0 pin as low to get -5V at the output. I want the DRVEN0 pin to be high.

Thanks and Regards,
Vaishak

  • 0
    TI__Genius 12130 points

    Hi Vaishak,

    Yes, you can do this through the "OVRD_CNTL" register. This register lets you ignore the temperature software, allowing you to write whatever value you want to the DAC. 

    You would write your overwrite data to registers 0x0B, 0x0C, 0x0D, 0x0E (if you want -5, you would write all Fs). Then, you would enable the overwrite, register 0x08 data 0x02. Let me know if you have any other questions.

    Thanks,
    Erin

  • 0 in reply to Erin Bowrie
    Prodigy 70 points

    Thanks.
    So I assume there won't be any problem to Change the voltage value from -3.7V to -5V through I2C lines keeping the DRVEN0 pin as high.

  • +1 in reply to Vaishak B
    TI__Genius 12130 points

    Hi Vaishak,

    Correct. Make sure you update the DAC overwrite data before enabling the overwrite, though, because by default the code is 0x000, and this would cause the DAC to output 0V. You can even program the DAC overwrite codes during your power-on sequence, and for the power-off sequence just enable the overwrite to drive the -5V output.

    Thanks,
    Erin

  • 0 in reply to Erin Bowrie
    Prodigy 70 points

    Hi Erin,
    I observed that FETDRV0 output of one of the GaN mode bias controller is not giving -5V output during power ON of the device. It is giving 0V as output. Where as FETDRV1 of the same bias controller gives -5V during initial power ON. Also,  Both enable pins (DRVEN0 and DRVEN1) are individually driven from microcontroller and both the pins are set to 0V during power ON. Why is the FETDRV0 not giving -5V as output during initial power ON ?

    But After programming the device through I2C, The required voltage can be seen at both the FETDRV outputs. ( i.e -3.7V and -2.8V) and also through I2C, I am able to program the device and get -5V output at both the FETDRV0 and 1 pins.
    Can you Please help me resolve this issue ?


    Thanks and Regards,
    Vaishak 

  • 0 in reply to Vaishak B
    TI__Genius 12130 points

    Hi Vaishak,

    If the DRVEN0 pin is grounded, it should be clamping the FETDRV0 pin to VSSB. Could you send me the I2C transactions you are sending to get the -5V output?

    Thanks,
    Erin

  • 0 in reply to Erin Bowrie
    Prodigy 70 points

    Hi Erin,
    Will send you the transactions shortly. 
    Also What would be the condition of FETDRV if DRVEN pins are kept floating ?

  • 0 in reply to Vaishak B
    TI__Genius 12130 points

    Hi Vaishak,

    If the FETDRV pins are floating there's a chance the signal can be read as high. If there's a chance the pin is floating at startup, I would recommend installing a weak pulldown resistor to ground the pin.

    Thanks,
    Erin

  • 0 in reply to Erin Bowrie
    Prodigy 70 points

    Hi Erin,
    Anyways the pin will be driving low during startup. Also, Can you tell me if there is any kind of software RESET for this IC ? We are observing this Only in this board. Other boards are fine.

    Thanks,
    Vaishak

  • 0 in reply to Vaishak B
    TI__Genius 12130 points

    Hi Vaishak,

    Just to make sure, it might be good to probe the DRVEN pin during startup. If it is only this board, perhaps there is something wrong with the driver on that pin. Along with that, also probing the FETDRV pin at the same time would be good to see the turn-on behavior.

    I've attached the software reset register:

    Thanks,
    Erin