SN74AXC8T245: SN74AXC8T245 and SN74AXC2T245 support for 1V2 to 1V8 in 1000Mbps GMII Interface

SHYAMKUMAR MURALEEDHARAN

Part Number: SN74AXC8T245
Other Parts Discussed in Thread: SN74AXC2T245, , TXV0108, SN74AVC8T245, TXV0106

Tool/software:

Hi TI Team,

I am planning to use SN74AXC8T245 / SN74AXC2T245 to level shift from 1V2 to 1V8 for 1000Mbps GMII interface in my design. As per the datasheet i have seen that its mentioned the level shifter can support upto 380Mbps when translating from 1V8 to 3V3.

Could you please clarify whether how much it can support when translating from 1V2 to 1V8?

Also please confirm whether i can use these level shifters for the 1000Mbps GMII interface?

Regards

Shyam

1 month ago

0 Jack Guan 1 month ago

TI__Mastermind 40076 points

Hi Shyam,

The supported data rate per the voltage corners can be determined through the relationship with tpd, and estimated through this FAQ: [FAQ] How can I estimate Data Rate Frequency not given for my voltage level?

There currently isn't a translator in our portfolio supporting 1Gbps, you may have to look through differential ended signaling to achieve these speeds.

Regards,

Jack

0 SHYAMKUMAR MURALEEDHARAN 1 month ago in reply to Jack Guan

Prodigy 70 points

Hi Jack,

I think you have wrongly taken the 1000Mbps I mentioned for the GMII interface in my initial question.

As per the SN74AXC8T245 datasheet, it has clearly mentioned that it can support 380Mbps when translating from 1V8 to 3V3. I think this 380Mbps is per bit of transfer and in our case as we are using GMII, we have eight RX and eight TX signals which needed to be level shifted.

Could you please clarify on the same?

Regards

Shyam

0 Jack Guan 1 month ago in reply to SHYAMKUMAR MURALEEDHARAN

TI__Mastermind 40076 points

Hi Shyam,

The data rate is given per channel for our devices. Are you suggesting that the1000Mbps is a total combination of all the 8 channels? If so, that would mean about ~125MHz per channel support which is 250Mbps equivalent. At the 1.2V to 1.8V voltage corner, there is also the TXV0106/ TXV0108/ SN74AVC8T245 that can be evaluated here.

Regards,

Jack

0 SHYAMKUMAR MURALEEDHARAN 1 month ago in reply to Jack Guan

Prodigy 70 points

Hi Jack,

Yes you are right, the data rate of 1000Mbps is the total combination of all the 8 channels. So it means i required 125Mhz (125Mbps as 1 bit per clock in my case) per channel.

I would like to know whether SN74AXC8T245 can support 180 - 200Mbps per channel for a safer data rate as there will be some PCB related constraints which affects the data rate.

If this level shifter can support 180 -200 Mbps per channel when shifting 1v2 to 1v8 and vice versa, then i can use it my design without any data rate issues.

Could you please help here?

Regards

Shyam

0 Jack Guan 1 month ago in reply to SHYAMKUMAR MURALEEDHARAN

TI__Mastermind 40076 points

Hi Shyam,

The datasheet did not characterize the max data rate of the AXC8T245 at 1.2V-1.8V, however through the FAQ I have provided, the estimation with1/tpd will not be sufficient enough to support the 125MHz/250Mbps given the tpd for this device (90Mbps through following the equation). Instead, the other devices listed, TXV0106/ TXV0108/ SN74AVC8T245, would be a better fit for your application instead.

Jack Guan said:
How can I estimate Data Rate Frequency not given for my voltage level?

Regards,

Jack

0 SHYAMKUMAR MURALEEDHARAN 1 month ago in reply to Jack Guan

Prodigy 70 points

Hi Jack,

Thanks for sharing the FAQ link.

But I have seen somewhere that the max data rate is calculated by the following equation. This is different than the FAQ link formula ie Max DR = 1/tpd.

Max Data rate = 1/ (2 x tpd)

Could you please check and confirm the same?

Regards

Shyam

0 Jack Guan 1 month ago in reply to SHYAMKUMAR MURALEEDHARAN

TI__Mastermind 40076 points

Hi Shyam,

The two equations are same, just in different units. 1/2 x tpd is applicable for MHz, while the FAQ that I have shared is in Mbps. I hope this clears up the confusion.

Regards,

Jack

Logic

Logic forum

SN74AXC8T245: SN74AXC8T245 and SN74AXC2T245 support for 1V2 to 1V8 in 1000Mbps GMII Interface