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Explanation As To Why the Crystal Does Not Oscillate on ADV7182 or ADV728x Systems After Powerup

When the ADV7182, ADV7280, ADV7280-M, ADV7281, ADV7281-M, ADV7281-MA, ADV7282 or ADV7282-M system is first powered, you will find that the 28.63636MHz crystal will not oscillate. This is expected behavior as per design.

This has surprised some customers as the older part, the ADV7180, did not operate in this manner. In ADV7180 systems the 28.63636MHz crystal oscillated immediately after power up.

This is because the ADV7182/ADV728x parts were designed to operate in a slightly different manner than the ADV7180.

When the ADV7182/ADV728x is first powered up it still remains in a software powerdown mode. In this powerdown mode the XTALP and XTALN pins are powered down. This results in the crystal not oscillating.

Running Analog Devices' recommended script forces the ADV7182/ADV728x out of powerdown mode. The write 0x00 to the User Sub Map register 0x0F forces theADV7182/ADV728x out of powerdown mode. After this write the crystal will start oscillating.

Comments
Anonymous
  • Yes, it is absolutely right, i have observed this behavior for ADV7180.

    only after chip is getting powered up, crystal is showing frequency 28.63636MHz. in power down mode it is not showing frequency even though supply is given to chip. chip will be powered up by two things 1. active High signal on PWRDWN  pin. or 2. PWRDWN bit is high in register 0x0F depending on the PDBP bit in register 0x0F.

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