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DP83869HM: DP83869HM: Power sequence requirement

Anandhu Vs
Prodigy 75 points
Part Number: DP83869HM
Other Parts Discussed in Thread: DP83869EVM

Tool/software:

Hi Team 

   I am using Ethernet PHY(DP83869HM) in RGMII mode and Two-Supply Configuration. I'm using VDDIO 3.3V

   I've a question on power sequencing,

VDDA2P5 - 2.5V

VDD1P1 - 1.1V

VDDIO - 3.3V

Can I supply /ramp-up all the voltages at the same time (VDDA2P5,VDD1P1 and VDDIO 3.3V at the same time)

Should I follow the Datasheet recommendation, i.e. VDDA2P5 and VDD1P1 are ramped up together and VDDIO(3.3V) later.

  • 0
    TI__Mastermind 19621 points

    Hi Anandhu,

    Thank you for submitting your query, I'm more than happy to assist.

    The timing diagram is a little misleading, please refer to Figure 1, taken from the current data sheet found online. The T2 time has a MAX of 50ms, meaning VDDIO must come up within 50ms of VDDA2P5 & VDD1P1. Note that there is no minimum requirement.

    To answer your question, yes; VDDA2P5, VDD1P1 and VDDIO 3.3V can all be powered on at the same time.

    Figure 1 - Taken from Section 8.3.1 Two-Supply Configuration of the data sheet

    Regards,

    Alvaro

  • 0 in reply to Alvaro (Al-vuh-roe) Reyes
    Prodigy 75 points

    Hi Alvaro

    Thank you for your response. Please clarify the below points for us.

    1. While analyzing the EVK reference design (PROC101C (005) _SCH_EVK.pdf) of TI, considering the propagation delay and the output capacitance, the three rails may not be powered on at the same time. Could you please advise on the same?

    2. What if the 3.3V reaches before 2.5V and 1.1V?

    3. Is it required to provide 2.5V and 1.1V together?

  • 0 in reply to Anandhu Vs
    TI__Mastermind 19621 points

    Hi Anandhu,

    Please find my replies below.

    1. They were probably following the data sheet diagram, but rest assured that all three supplies can be powered at the same time.

    2. While not recommended, I have gone into lab and tried this out with our DP83869EVM by using external power supplies, and suppling the 3.3V rail several seconds before turning on the 2.5V and 1.1V rail. The PHY was still able to power on, link up, and transmit packets successfully.

    3. Yes. We have noticed that if you power one of these rails without the other (e.g. power 1.1V before 2.5V), a ~0.8V pedestal voltage can be seen coming out of the 2.5V pin from the PHY. This will not damage the PHY or cause functional issues. 

    Regards,

    Alvaro