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Please tell me about Video DAC (ADV7125) current limit.

Category: Datasheet/Specs
Product Number: ADV7125
Software Version: non

I believe that the current control of the RGB analog signal output can be controlled using the RSET pin.
Is it possible to make it smaller than 530Ω under the following conditions?
If it is possible to make it smaller, could you please tell me how small it can be made? (I want to increase the current flowing.)

-conditions-
SYNC pin=low, VAA=3.3V

(Intent of question)
The value of RSET can be calculated using the following formula
I interpret it as IOR, IOB,IOG (mA) = 7989.6 × VREF (V)/RSET (Ω)

FEATURES has the following information
It says DAC output current range:2.0mA to 26.5mA, is max26.5mA the limit?

The value listed in FEATURES is range:2.0mA to 26.5mA, so
According to this description, if the SYNC pin is set to High, up to 26.5mA can be used.

When SYNC pin is set to low, it can be used up to 18.5mA ←When SYNC pin is set to low, 18.5mA is the limit value?
In the circuit example in the data sheet, the resistance value of RSET is 530Ω.
7989.6 × VREF (V)/RSET (Ω)=7989.6 x 1.235 / 530 =18.61mA ←Exceeds 18.5mA

I think my interpretation is fundamentally wrong, so I'd like to confirm.
Increase the current (analog signal voltage value Vp-p) as much as possible.
The purpose is to strengthen noise resistance.

Parents Reply
  • Hi,

    From the formula,

    IOG (mA) = 11,444.8 × VREF (V)/RSET (Ω) (SYNC being asserted)
    with Rset = 530 and Rload = 37.5Ohm

    gives you (37.5 * 11444 * 1.235 / 530) / 1000 = 1.000 Vpp

    See Figure 5 in the data sheet.

    Assuming green channel with sync included,

    510 --> 1.039 Vpp
    530 --> 1.000 Vpp
    560 --> 0.946 Vpp

    Thanks,
    Dharani S

Children
  • Dear Dharani S

    Thank you for your kind calculation formula.

    I can understand how to calculate the expected output voltage from the set value.

    How can I determine whether this setting either output voltage or output current are okay for the ADV7125?

    Or is there no limit for ADV7125?

  • Hi,

    As stated, we do not test this or specify these limits beyond what is defined in the data sheet in our eval board.

    While looking at the ADV7125 datasheet, Figure 5 and Table 7 we see that the red and blue DAC output has will output has a voltage range of 0 - 0.975V. The green has the same output except it is positively offset by 0.271V to give room for the sync pulse.

    Make note that the white level output current level, for red and blue it's 0-18.67mA. For green it's 7.2-26mA for black to white.

    This is all done with Rset=560 Ohms. The DAC outputs are limited to 1.4. so this is what we'd do.

    Could you please check from your side for this case and share us your results if it is not as expected?

    Thanks,
    Dharani S