DP83867IR: Power up timing

ryuji asano

Part Number: DP83867IR

Hi, Expart.

Please help us.

My customer's questons are below.

1)
We saw the Figure.1.(Below chart)
Figure.1 is the sequence of power up timing. (Document#: SNLS484E)
Figure.1 shows input XI clock before VDD power on.
Should we need to input XI clock signal before VDD input?

2)
We don't know about sequence rules when power off.
Don't we have to think about something to special sequence？
Don't we have to care about sequence rules when power off?

3)
We know DP83867 is capable of operating with two or three power supplies.
We will operating with two-supply.
What should we be careful with operating with two-supply?
Is there nothing to worry about?

4)
Is the DP83867I only receiving 125 MHz from the external clock and output it?
Can the DP83867I generate 125 MHz independently and output it?

Best Regards,

Ryuji

over 8 years ago

0 Ross Pimentel over 8 years ago

TI__Mastermind 23675 points

Hi Ryuji,

Here are the answers:
1. If using a crystal across XI and XO, you do not need to worry about this. If using an external oscillator, you will need to provide the clock right at power-up.

2. No power-off sequence.

3. When operating with two supply, there is no requirement on power-up sequence.

4. The DP83867I must receive a 25MHz clock on the XI pin. The RX_CLK pin when in RGMII operation can be 125MHz for 1Gbps, 25MHz for 100Mbps, and 2.5MHz for 10Mbps links. The TX_CLK will output 125MHz for 1Gbps, 25MHz for 100Mbps and 2.5MHz for 10Mbps links.

Kind regards,
Ross

0 ryuji asano over 8 years ago in reply to Ross Pimentel

Intellectual 800 points

Hi Ross-san,

Thank you for your kind answer.
Please teach me more.

>1. If using a crystal across XI and XO, you do not need to worry about this. If using an external oscillator, you will need to provide the clock right at power-up.

If using an external oscillator, should I provide clock after power-up?
(Our concern is input sequence)
Which one should we input first? (Clock signal? or Power off?)

In the case of using external oscillator,
How many seconds of time between input clock and power-off?
(We would like to know the time allowed)

Best regards,
Ryuji

0 ryuji asano over 8 years ago in reply to ryuji asano

Intellectual 800 points

Hi Ross-san,

I'm sorry to bother you, but could you help me?
My customer wants answer.
I am waiting for your answer.

Best regards,

Ryuji

0 Geet Modi over 8 years ago in reply to ryuji asano

TI__Mastermind 26320 points

Hi Ryuji,

Clock shall be present before the power-up.

No sequencing needed at power-off.

Regards,
Geet

0 NAOKI AOYAMA over 8 years ago in reply to Geet Modi

Guru 11215 points

Hello,

Allow me to cut in.
Our customer use the DP83867 with two supply configuration and use an oscillator for clock in.
The customer supply the voltage of oscillator by VDDIO as 1.8V. It is same supply line.
So, the clock is a little bit delay from the VDDIO input.

Does it damage the device or impact for performance of the device?

The start-up sequence as follows.
/ VDDIO as 1.8V
/ Clock in
/ VDDA1P1 and VDDA2P5

Best Regards,
Naoki Aoyama

0 NAOKI AOYAMA over 8 years ago in reply to Geet Modi

Guru 11215 points

Hello,

I change a question.
When using a crystal source, how long does it take to start oscillation from power-on?

I will check the spec of the oscillator. I will compare the speed of oscillator and crystal source.

Regards,
Naoki Aoyama

0 Ross Pimentel over 8 years ago in reply to NAOKI AOYAMA

TI__Mastermind 23675 points

Hi Aoyama-san,

The crystal start-up is dependent on the amount of gain your total crystal network has.
I cannot say how long it is because it depend on your circuit and board. However, you should see small oscillation start right at power-up and it gradually gain up while going through the POR process, until it reached full range.

Best regards,
Ross

Interface

Interface forum

DP83867IR: Power up timing