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THS7347 VGA buffer

Bala3458
Intellectual 350 points
Other Parts Discussed in Thread: THS7347

Hello,

We are using THS7347 for buffered VGA output on our monitor. Actually we need two VGA outputs simultaneously. Is it possible to get dual output from THS7347 without I2C program?

And we are trying to write I2C command to this IC.

  • IC's VDD and +VA  are connected with +5V input. 
  • SDA and SCL are pulled up with 2.7K, and with 100E and 22pF RC filter as mentioned in datasheet. 
  • Both I2C address pins are grounded. So the slave address is 0x58. 

 For address transfer we didn't get acknowledgement from IC. Please check attached scope image of SDA SDL. What could be the problem. Please give answer to solve this issues.

Regards,

Bala

  • 0
    TI__Genius 15975 points

    Hi Bala,

    The Monitor output of THS7347 can be used to drive as two VGA outputs without I2C programming. The monitor output is enabled by default upon power on by connecting the PUC pin to VDD. You would need to connect the Monitor ouput pin and SAG output pin together to get a gain of 6dB and then ac couple it as two separate VGA output paths.

    Is it be possible that you could upload the I2C signal path diagram for both the master and THS7347? It is possible that the Master is preventing the THS7347 from pulling low at the 9th clock cycle.

    Best Regards,

    Rohit 

  • 0 in reply to Rohit Bhat
    Intellectual 350 points

    Hi Rohit,

    Thanks for your answer.

    As of now we connected one display with THS7347 monitor output with 75E series resistor on RGB lines and 75E termination on display side. If we want to connect two display this series 75E resistor is required or not?

    We may disconnect any one of the monitor for some condition. Due to the gain, will it affect the connected monitor brightness (Will it show as high bright?). 

    Please find an attached schematic of THS7347 I2C section. In I2C master program after 8 bit address transfer, SDA pin will change to as a input pin. So it will allow to THS7347 to pull low for ACK. What could be the problem in this?

    Regards,

    Bala

  • 0 in reply to Bala3458
    TI__Genius 15975 points

    Hi Bala,

    I think you would need to have the 75 ohm resistor when connecting two monitors. See the attached diagram below.

    I don't think it should ideally affect the connected monitor brightness because in the Monitor pass through path because you would see a resistive divider due to 75/(75+75), there is effectively 20log(1/2) = -6dB gain which compensates for the 6dB gain in the amplifier. 

    In the I2C waveform, it seems that the THS7347 is pulling low on the 9th clock but not sufficiently enough when the SCL is high. Does the master go high impedance when it is changed to input pin?

    Best Regards,

    Rohit

     

  • 0 in reply to Rohit Bhat
    Intellectual 350 points

    Hi Rohit,

    Thank you for your answers. We checked with two monitors on monitor output. Brightness not getting affected. But we are facing some shadow image on display. We are checking on this issue.

    In I2C THS7347 IC's SDA pin got affected in somehow. That's why SDA signal is not reaching zero level also. after changing new IC its clear.

    Regards,

    Bala