[ADV7480] Special situation in power supply sequence.

Hi Tamu San,

        Please let me know, Whether this 1.8V power supply down situation is occuring automatically at customer end Or customer is making  this 1.8V power suply down condition ?

       As per expert comment " If customer power up all the 3.3 V supplies together, and all the 1.8V supplies together, and always keep the 3.3V supplies above the 1.8V supplies during the transition, it should be fine.

      They must also make sure to keep the reset pin held low for at least 5ms after the supplies are all fully up and stable, as described in the datasheet.

      Also please refer this thread (ADV7480)Pin status while 3.3V=ON & 1.8V=OFF - Q&A - Video - EngineerZone (analog.com)

Thanks,

Poornima

Hi Poornima-san,

Thank you for your reply.

> Please let me know, Whether this 1.8V power supply down situation is occuring automatically at customer end Or customer is making this 1.8V power suply down condition ?
=>The customer says that the situation occurs due to the circuit circumstances of his design.
So if the situation doesn't cause any problems for the ADV7480, he will not fix the situation.
If the situation may cause problems for the ADV7480, I will tell the customer to fix the situation.
But we don't know whether the situation may cause problems or not. So we ask these questions.

Questions:
#1: Can this situation (the blue circle) be allowed for ADV7480?

#2: After the situation, then the Reset is released (RESET pin becomes High) and initial register settings are completed (the yellow circle).
After that, can ADV7480 work normaly again?

Please refer the attached file "ADV7480_Questions.xlsx" at my previous comment.

Thank you!
Best regards.
Tamu

Hi Tamu San,

         Please find the below comments,

I believe, the blue circle doesn't cause any problem to ADV7480.

As per expert comment, According to the specification we need to make sure the RESET pin with below conditions,

When they assert Reset, the level on the /RESET pin must be below Vil (0.8V max) for at least 5ms while the 3.3V and 1.8V supplies are stable.

And after a Reset, when the level on the /RESET pin is above Vih (2V min) and they must wait at least 5ms before starting doing I2C writes to the chip.

If above condition are met by RESET pin, then ADV7480 would work normally.

Note: 

 RESET goes low then high after powered up  => This is power up Reset case.

 Then RESET goes low again and goes high => Reset during normal operation.

 If RESET is held low after Powerup then how RESET will happen in the chip.

Thanks,

Poornima

Thank you !