ADV7391 High Drive Compensation Pin Connection

Dear Analog Devices Team

We are designing a board which uses ADV7391BCPZ Video Encoder and ADA4433-1BCPZ-R2 SD Video filter amplifier.

Below are the few observation :

  1. Application circuit example in ADV7391BCPZ datasheet recommends to connect the RSET to 510Ohm and COMP pin to 2.2nF which will be pulled to VAA ( 3.3V ) for full drive mode.
  2. In the development board schematics also you have made use of full drive option by connecting COMP to VAA and keeping RSET to 510Ohm.
  3. For the low drive operation of ADV7391BCPZ the COMP pin status is not mentioned in the datasheet. I.e whether it should be connected to VAA or Ground.
  4. When we referred ADA4433 datasheets Application circuit ( Page No. 21 of 28, Figure 53) for low drive operation the COMP pin has been connected to Ground through 2.2nF capacitor.
  5. We have set voltage at IN- pin of ADA4433-1 as 0.5V using a recommended biasing network and output to 1Vp-p.
  6. So, In high drive we connect COMP to VAA using 2.2nF capacitor and in low drive mode we connect COMP to Ground using 2.2nF capacitor ?? Is my understanding correct ?
  7. Please mention the RSET and COMP pin status in High Drive and Low drive mode.

With Regards

Bhanuprakash Nayak

Member Technical-Hardware

  • 0
    •  Analog Employees 
    on Aug 22, 2014 6:59 AM over 6 years ago

    Hi, Bhanuprakash,

       it is clear for the COMP and Rset connection on the ADV739X datasheet pin definition:

    RSET Controls the amplitudes of the DAC 1, DAC 2, and DAC 3 outputs. For full-drive operation (for example, into a 37.5 Ω load), a 510 Ω resistor must be connected from RSET to AGND. For low-drive operation (for example, into a 300 Ω load), a 4.12 kΩ resistor must be connected from RSET to AGND

    COMP Compensation Pin. Connect a 2.2 nF capacitor from COMP to VAA;

    The ADV739x contains three DACs. All three DACs can be configured to operate in full-drive mode. Full-drive mode is defined as 34.7 mA full-scale current into a 37.5 Ω load, RL. Full drive is the recommended mode of operation for the DACs.

    Alternatively, all three DACs can be configured to operate in low-drive mode. Low-drive mode is defined as 4.33 mA full-scale current into a 300 Ω load, RL.

    The ADV739x contains an RSET pin. A resistor connected between the RSET pin and AGND is used to control the full-scale output current and, therefore, the output voltage levels of DAC 1, DAC 2, and DAC 3. For full-drive operation, RSET must have a value of 510 Ω and RL must have a value of 37.5 Ω. For low-drive opera-tion, RSET must have a value of 4.12 kΩ, and RL must have a value of 300 Ω. The resistor connected to the RSET pin should have a 1% tolerance.

    The ADV739x contains a compensation pin, COMP. A 2.2 nF compensation capacitor should be connected from the COMP pin to VAA.

    Also you can see the reference schematics design on ADV739X datasheet Rev E page 72 and &3, Fig- 93 and 94;

    Regards

    Joseph

  • Dear Joseph

    Thanks for you quick reply,

    I do agree with your answer but my major concern was regarding ADA4433 application circuit.


    I referred ADA4433 datasheets Application circuit ( Page No. 21 of 28, Figure 53) for low drive operation the COMP pin has been connected to Ground through 2.2nF capacitor.


    Why is this done ??


    With Regards

    Bhanuprakash Nayak

  • Dear Joseph

    Please find the below link for ADA4432-1/ADA4433-1 component datasheet.

    http://www.analog.com/static/imported-files/data_sheets/ADA4432-1_4433-1.pdf

    Please refer to figure 53 which uses ADV7391 component, in which COMP pin is connected to ground using 2.2nF capacitor.

    Do you see there is a typo in ADA4432-1/ADA4433-1 component datasheet ?

    Regards

    Bhanuprakash Nayak

  • 0
    •  Analog Employees 
    on Aug 22, 2014 5:24 PM over 6 years ago

    Hi, Bhanuprakash,

        seems there is some mistake for the ADA4433 application circuit, i checked the ADA4432 amd ADA4433 products web, the ADA4433 application circuit should be from the CN0264 as below web link

     

     

     

     

     

    Circuit Note | CN0264 | A Robust Solution for Transmitting Composite Video with Output Short-to-Battery Protection | Ana…

     

     

     

     

    on the system block, it is same as the ADA4432/4433 datasheet system block, but you downalod the whole design documents and check the schematics, the COMP connection is same as ADV739X datasheet;

    EVAL-CN0264-EB1Z-PADSSchematic-Rev0.pdf page 2

  • Hi Joseph

    Thanks for the clarification.

    With Regards

    Bhanuprakash Nayak