DP83TG720S-Q1: PHY Power Down Issue.

Hello,

I have a few questions about the setup:

• How is the PHY chip being powered down?
• After voltage rails go to 0 V does the square wave signal persist?
• When putting the MAC in high z impact the occurence of the square wave signal?

Regards,

Avtar

• The PHY power-down is triggered by the primary power supply power-down sequence, followed by the power-down sequence of other power supplies. However, when the abnormal square wave appears, all PHY power supplies are stable within the normal range.

• After the power-down, the square wave does not continue to exist. In fact, looking at the test waveform, the square wave only appears for a short period of time and disappears while the power supplies remain stable.

• In fact, there is a TI level shifter, TXV0106, between the RXD and the MAC input, converting 1.8V to 3.3V. This means that the PHY is experiencing the high-impedance input of the level shifter.

Hello,

Can you try removing TI level shifter and probe the pin to see if PHY is causing this square wave or if level shifter is causing this?

Regards,
Avtar

There is a series source termination resistor between the level shifter and the PHY's RX_CTRL pin. After removing this resistor and performing a power-down test, I found that the abnormal square wave still appears on the PHY's RX_CTRL pin, while there is no waveform on the other side.

Hi,

Thanks for clarifying, are there any functional issues with the abnormal square wave? Unfortunately we cant predict the PHY behavior when it is outside our tested power down specs. 

Regards,

Avtar

It is not yet certain whether this will result in erroneous data that could affect functionality. What are your power-down testing specifications?

My apologies by specs I meant power down method, we do not have power down testing specifications. Can testing be down to see if this affects functionality?

We can perform a power-down test, but are there any other methods to investigate the cause of this issue with the PHY? Our power-down procedure follows a standard power-down logic, where the external power supply shuts down, triggering the power-down of subsequent stages.

Yes please perform a power down test and check for any functionality issues. This abnormal square wave isn't present at all during normal transmission correct?

Regards,

Avtar

Yes, during normal transmission, we haven't observed any abnormal square waves. They only appear right before power-down and last for a few microseconds.

If there is any packet loss, packet error, or link down please let me know, apart from that it is hard to diagnose this issue as we can't predict PHY behavior in scenarios outside those that have been tested.