SN74AUCH244: SN74AUCH244: For RGMII bus driver

Ju Ward

Part Number: SN74AUCH244

Hi TI support team

In our applciation the RGMII interface from CPU travels a long way on the PCB so we need to add a bus line driver(SN74AUCH244) for it.

1. Is there a layout guide or a application note for the bus driver?

2. What is the suggestion for placement? close to CPU or close to PHY?

Note : Our layout length of trace is about 12000mil, but CPU's specification of length is 8000mil

Thanks

over 4 years ago

0 Clemens Ladisch over 4 years ago

Guru 316690 points

Application of the Texas Instruments AUC Sub-1-V Little Logic Devices
Designing With TI Ultra-Low-Voltage CMOS (AUC) Octals and Widebus Devices

A 12 in trace could have a capacitance of more than 30 pF. If the drive strength of the CPU and the '244 are the same, you could put the driver in the middle so that both share the load. But I guess AUC outputs are stronger (while switching, AUC outputs have an output impedance that is lower than their DC drive strength), so the driver should be nearer the CPU.

0 Ju Ward over 4 years ago in reply to Clemens Ladisch

Prodigy 75 points

Hi TI support team

1. Is SN74AUCH244 suitable for RGMII driver? No frequency support data in datasheet, so what is the bandwidth(BW) support?

2. Do your customer ever choose SN74AUCH244 for RGMII driver? Any side effect happen?

Like maybe need to tune skew for RGMII_TX_data/RGMII_RX_data?

3. I see the Cpd is 22pF(VCC=1.8V / f=10MHz), Is the Cpd large for RGMII signal? Could you provide Cpd for about 125MHz?

Thanks

0 Ju Ward over 4 years ago in reply to Ju Ward

Prodigy 75 points

0 Ju Ward over 4 years ago in reply to Ju Ward

Prodigy 75 points

Hi TI support team

RGMII_TX_CLK is 125MHz

RGMII speed = 1000Mbit/sec

Thanks

0 Dylan Hubbard over 4 years ago in reply to Ju Ward

TI__Mastermind 45725 points

Hey Ju,

BW isn't something we spec for our devices, but here is an FAQ that should help you estimate it (AUC is our faster Logic family).

The device you chose is a generic 8 channel buffer that can be used in a wide variety of applications so its possible someone has used it for RGMII. Its one of our fastest buffers so it should work well with RGMII.

Cpd is a variable for dynamic power consumption, there is only one value to provide and its the one located in the data sheet. You should be able to use that value in your calculations without any issue.

Logic

Logic forum

SN74AUCH244: SN74AUCH244: For RGMII bus driver