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THVD8000: questions

Allan Fan
Expert 7080 points
Part Number: THVD8000

Tool/software:

Hi experts,

May I check with you;

1. how to estimate the driver output voltage V_od ? The Vcc is 3.3V in customer design.

2. How to choose the power rating of the termination resistor e.g. the 120 ohm R12 on the EVM?  Customer design is 3.3V for Vcc

Thanks,

Allan

  • 0
    TI__Guru 72751 points

    Hi Allen,

    Allan Fan said:

    1. how to estimate the driver output voltage V_od ? The Vcc is 3.3V in customer design.

    I had to look up the data in our internal database for validation. We didn't have 3.3V test cases, closest one was 3V. If you had 3.3V your VoD would be a little bit higher.

    At 25C at 3V the average COD for a 54 ohm load is around 1.8V

    Same as above but with a 100 ohm load, VoD is around 2.3V

    Allan Fan said:

    2. How to choose the power rating of the termination resistor e.g. the 120 ohm R12 on the EVM?  Customer design is 3.3V for Vcc

    You can do V^2/R to calculate power. I would probably just use Vcc as the V instead of the VoD since that would give you more margin for error. If you have termination on both sides 120//120 would be 60 ohms.

    So if you had 3.3V and Req=60 ohms then the power rating is around 182mW

    -Bobby

  • 0 in reply to BOBBY
    TI__Expert 7080 points

    Hi Bobby,

    Some more questions would like to clarify;

    3. customer design will need THVD8000 carrier frequency to be changeable by software to multiple different frequencies to prevent communication failure.

      • According the datasheet, the F_SET pin voltage is 785mV for 1.5k~80k Ohm pull-down resistor. May we use some MCU DAC output to connect to F_SET through some resistor network to have the modulation frequency controllable by the DAC voltage?
      • Or is there some suggested methods for software controllable modulation frequency?

    About the V_od, customer got the answer for real measurement at 3V for 54 ohm load (1.8V) and for 100 ohm load (2.3V)

      • We will have 120 ohm termination resistor in our design ( the link partner also 120 ohm ). May I assume the load resistor is equivalent to 60 ohm and the V_od can be estimated as between 1.8V and 2.3V ?

    Regards,

    Allan

  • 0 in reply to Allan Fan
    TI__Guru 72751 points
    Allan Fan said:
    We will have 120 ohm termination resistor in our design ( the link partner also 120 ohm ). May I assume the load resistor is equivalent to 60 ohm and the V_od can be estimated as between 1.8V and 2.3V ?

    Yes, it will likely be a little larger than 1.8V but won't be larger than 2.3V. 

    Allan Fan said:
    • According the datasheet, the F_SET pin voltage is 785mV for 1.5k~80k Ohm pull-down resistor. May we use some MCU DAC output to connect to F_SET through some resistor network to have the modulation frequency controllable by the DAC voltage?
    • Or is there some suggested methods for software controllable modulation frequency?

    Yes, you technically could modify it as long as you don't go soutide of the boundaries of 1.5k to 77k ohms. I would probably try to do this using a multiplexer tied to different resistors to GND. The carrier frequency isn't very precise though, it can vary by 25% of your target/desired frequency.

    -Bobby