ADV739x: Output protection when using the Full Drive Option

Hi,

We don't know what type of impact it will create and note that to avoid crosstalk between the DAC outputs, it is recommended that as much space as possible be left between the traces connected to the DAC output pins. Adding ground traces between the DAC output traces is also recommended. These details are already provided in the ADV739x datasheet from Page69 and also refer section "PRINTED CIRCUIT BOARD (PCB) LAYOUT"

 In general, you want to keep digital switching noise away from any analog signal, the digital traces need to referenced to ground planes and kept away from Vaa and PVdd to keep switching noise away from those power rails.

As per expert comment "ADV7393 has a DAC output designed for 37.5 or 300 Ohm loads.  Any ESD protection as long as it meets the voltage limits should work.    You just have to make sure the protection does not effect the higher frequency components of the signal. 

The 37.5 Ohm load circuit is harder to protect since there is no series resistance in the signal path for the ESD protection to work against.  I would design the part for 300 Ohm load, buffers and 75 Ohm series resistors.  Then put the true ESD protection on the output side of the series resistors.   There are any number of bridge ESD protection devices you can use as long as they do not effect the frequency components of the signal"

Thanks,

Poornima

Hi, Poornima
Thankyou for replay.

Our customer uses the ADV7390 with the FULL DRIVE OPTION, which means that the ADV7390 output is directly connected to an RCA connector.
In this case, we have the following two questions:

Q1
When the RCA connector is shorted to GND, does the ADV7390 have any protect funcntion and no problem from the Short to GND event?

Q2
When another Video DAC output is mistakenly connected to the RCA connector, does the ADV7390 have any protect funcntion and no problem from the event?
(For example, if another camera output RCA connector is connected to the output RCA connector of the ADV7390)

If the DAC output pin of the ADV7390 cannot be protected when the above two events occur, and an external buffer (such as the ADA4432-1) is required to protect it, please let me know.

best regards
AimPoint.

Hi,

   Above use case need to be check with part specialist.

   As per expert comment, "Shorting the analog outputs to ground when the DACS are enabled, It would damage the part" .

 Note: ADI cannot guarantee operation if the circuit is not implemented as shown in the specifications.

Thanks,

Poornima

Hi, Poornima
Thankyou for half answer.

From your explanation, we understand that the ADV7390 does not have output protection.

So Q1 is clearly the problem.

However, what about Q2?
We are waiting for an expert's answer.

best regards
AimPoint.

Hi,

  Apologies for the delayed response, We will check with part specialist and let you know about it.

Thanks,

Poornima

Hi, Poornima
Thankyou for replay.

we wait for a Q2 answer from specialist.

best regards
AimPoint.

Hi,

  Please refer below check points for question 2,

The ADV7390 is a video DAC designed to output analog video signals. When it comes to protection against incorrect connections, such as another video DAC output being connected to its RCA output, here are some key considerations:
1. **ADV7390 Protection:**
The ADV7390 does not have specific internal protection features designed to handle scenarios where another video DAC output is connected to its output. This could potentially lead to issues such as signal conflicts, excessive current draw, or damage to the DAC if the external source outputs higher than expected voltages.
2. **Potential Issues:**
- **Signal Conflict:** When two video DACs are connected to each other, there could be conflicts or interference between the signals, potentially degrading the video quality or causing operational issues.

- **Current Overload:** If one DAC output is driving the output of the ADV7390, it might exceed the current handling capability of the ADV7390, leading to potential damage.
3. **External Protection:**
To safeguard the ADV7390 from potential damage and ensure reliable operation, using an external buffer or protection circuitry is advisable. The ADA4432-1, which is a high-performance buffer, can be used to isolate the ADV7390 output from other external sources. This approach helps in several ways:

- **Isolation:** It isolates the ADV7390 from any external signal sources, preventing conflicts and potential damage.

- **Signal Integrity:** It maintains signal integrity by buffering and driving the output correctly without interference from external connections.
4. **Best Practices:**
- **Design for Protection:** In your design, consider incorporating buffers or protection circuits to handle situations where unintended connections might occur.

- **Avoid Direct Connections:** Ensure that the output of the ADV7390 is not directly connected to other DAC outputs or sources that are not designed to interface with it.

In summary, the ADV7390 does not have built-in protection for such scenarios, and it is recommended to use an external buffer like the ADA4432-1 to provide isolation and protection against potential damage from incorrect connections.

Thanks,

Poornima

Hi, Poornima
Thankyou for answer.

Thank you for considering the various conditions. I now have a better understanding.

best regards
AimPoint.