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THS7373: THS7373 design questions

user4980781
Prodigy 10 points

Part Number: THS7373

Hello,

I have some questins with THS7373 design need your help.

1.Can i use two 150 ohm pull down resister in RGB signal torouting RGB trace impedance with 37.5 ohm and 50 ohm?

2.Page 38 (Cout =330uF) and Page 42 ( Cout = 470uF) of THS7373 datasheet, the Cout pin + direction is difference, which one is right?

3.Page 42 of THS7373 datasheet  demo circuit has use two capacitors ( 470uF and 0.1uF), do they need to implement at the same time?

   Does 470uF design for low frequency bandwidth and 01uF for high frequency bandwidth?

4.Can i use 0,1uF MLCC as Cout for 1920x1200 resolution?

5.Does Cout is necessary? why i need to use it?

Thanks

Regards

C. A. Lai

  

  • 0
    TI__Genius 15975 points

    Hi Lai,

    To answer your questions:

    1. I think it might be possible to use two 150 ohm pull down resistor in RGB signal to route RGB trace impedance with 37.5ohm and 50ohm. However, is there a limitation in making the trace characteristic impedance (Zo) as 75-ohms?

    Also, it might be possible that you run into output filter flatness issues with the current approach, if you terminate the other end of the 75-ohm cable with 75-ohms impedance. In your current approach, you could see 150-ohm input and 50-ohm output impedance for the filter instead of the designed 150-ohm input and 150-ohm output for the filter, while terminating the other end of the cable with 75-ohms. Also, the overall amplitude seen at the other end of the 75-ohm cable will be lower resulting in lower picture brightness. Would it be possible to use the below output filter scheme instead for this?

    2. The Cout pin + direction on Page 42 is the right one.

    3. Yes, the implementation of two capacitors (470uF and 0.1uF) is at the same time and is for low frequency cut-off bandwidth. For video signals, you should not see attenuation in the 24-30Hz frequency range while ac coupling due to the slower frame rates in the video standard, and these capacitors mainly help address this.

    4. I would not recommend using only 0.1uF MLCC as Cout for 1920x1200 resolution, but instead recommend both the 470uF or 220uF and 0.1uF. It is mainly required for the reason mentioned in Ans 3 so that there is as low an attenuation seen in the 24-30Hz frequency range.

    5. If you do not plan on AC coupling at the output, then Cout is not necessary. However, there will be DC currents flowing from the output along the cable to the end equipment, when you are not AC coupling. You might want to read pages 36 to 38 in the THS7373 datasheet to understand the difference between the DC coupled and AC coupled case for output coupling.

    Best Regards,

    Rohit