ADV7480: Intermediate voltage supply during power down sequence.

Hi,

  As per expert comment, "The device is only characterized at 1.8V and 3.3V but it will work at an intermediate voltage and we don't characterize it there" at (+) Digital Inputs logic "1" voltage is higher than DVDDIO and digital input logic "0" voltage is lower than 0V on ADV7182&ADV7182A digital input pins - Q&A - Video - EngineerZone

Thanks,

Poornima

Hi Poornima.
Thank you for your reply.

Let me check a few more things.
You are correct that the intermediate voltage is “not characterized”.
However, as mentioned above, during the intermediate voltage period, #RESET is asserted, so we don't expect it to work.

What I would like to confirm is that
”device not damage” when the following conditions are achieved.
・High rate line (3.3V) > Low rate line (1.8V)
・Intermediate voltage is within the range of electrical characteristics
・RESET is asserted during the intermediate voltage supply period

Bset Regards
aimPoint

Hi,

  1)High rate line (3.3V) > Low rate line (1.8V)

As per expert comment "Basic rule to follow is that the 1.8V rail cannot exceed the 3.3V rail. This applies to both power up and power down sequences. 

 If the power sequence is backwards then current will flow from the 1.8V rail through the ESD protection diodes into the 3.3V rail.  Over multiple hits and delays from 1.8 to 3.3 rail rise times and 1.8V source impedance you might cause damage to the part.  So it is recommended to use the power up sequence as shown in specification for example "if 1.8V rail exceeds 3.3V rail then there will be excessive current flow from the 1.8V supply to the 3.3V rail.  If this occurs over an excessive amount of time this flow might cause thermal damage".

Hi Poornima.
Thank you for your detailed explanation. The items you pointed out have been followed.
Here is the confirmation again.

■Question 1:
Could the ADV7480 be damaged by the 3.3V supply stagnating at an intermediate voltage instead of monotonically decreasing during power down? (Is there a problem?)

■ Question 2:
Is there a possibility that the ADV7480 will be damaged by the following power-down sequence waveforms? (Is there a problem?)

Note 1: The “POWER-DOWN SEQUENCE” provision in the datasheet is satisfied.
Note 2: The RESET pin is held Low.
Note 2: The 3.3V power supply is at an intermediate voltage of approximately 1.3V for several 100msec.

Bset Regards
aimPoint

Hi,

 Question 1)

 Kindly note that, the device is characterized only at 1.8V and 3.3V and intermediate voltage are not characterized.

  According to the datasheet, the device operates within certain voltage ranges, and the recommended power-down sequence generally involves a gradual reduction in voltage. If the 3.3V supply stagnating at an intermediate voltage, it may create conditions where the chip cannot safely transition to a powered-down state, potentially leading to failure in one of its power rail or logic circuits.

Note: ADV7480 is generally designed to handle a smooth power-down process where the supply voltages, including 3.3V, decrease in a controlled manner.

Question 2)

    As stated, Power supplies can damage ADV7480 part only when lower rated supply(1.8V) exceeds the higher rated supply(3.3V)

   But we need to check with expert about this Note 2: "The 3.3V power supply is at an intermediate voltage of approximately 1.3V for several 100msec".

Thanks,

Poornima

Hi Poornima.
Thank you for your reply.

We have accepted your answer to question 1).

Please continue to check with the experts regarding question 2).
We will await a response from the expert.

Bset Regards
aimPoint

Hi,

  Thank You. We will check and let you know the update from expert.

Thanks,

Poornima