I need to run video through a SN74AVC32T254 at 165Mb. i am powering both sides of the device with 2.5V. My concern is that i need to keep the data and the clock aligned, and therefore would like to run the clock through the device. The clock is running at 165MHz (or effectively 330Mb). The data sheet says that any translation to 2.5V will limit the data rate to 200Mb, so it appears that i have a problem. However, the data sheet also says that 1.8V to 3.3V translation will run at 380Mb, but the Tpd of the device appears to be almost identical for 1.8V to 3.3V as it does for 2.5V to 2.5V. Could you please explain why the data rate through the device is limited to 200Mb when both supplies are 2.5V? Or can i run a clock at 165MHz (330Mb) through the device with no problem? And if so, why?
For this device you can think of it going through two standard '245 logic buffers. VCCA powers the first logic buffer VCCB powers the second logic buffer. First let's address the tpd's.
If you have the first buffer powered at 1.8V that one is going to have a prop delay of "x+2". The second buffer powered by 3.3V that is going to have a prop delay of "x". Your total prop delay is (x+x+2). If you have both buffers powered by a 2.5V VCC your have prop delays of (x+1) + (x+1) or (x+x+2). This is because at 2.5V. the prop delay of each buffer is performaning somewhere between how a 3.3V or 1.8V powered buffer is individually. In general the lower the voltage the slower it is going to be.
The data rate is less about the prop delay and more about how fast the device can switch. The switching speed is influenced by the lowest voltage on any one rail.
Since translation is not really needed in this case. You may want to consider one of our standard buffers/transceivers.
SN74ALVCH32245 - Transceiver (bidirectional)
SN74AUC32245 - Transceiver
SN74AUC32244 - Buffer (one direction)
Thanks for the help with this. I am thinking that the AUC32245 will be a good choice since it is pin compatible with the 32T245. The AUC32244 would also be a good choice, but i am not sure if it is pin compatile. Could you confirm?
What i found interesting is that the 32T245 had a max bit rate through the device, but the AUC32245 and AUC32244 only specify Tpd. Why is that, and how do i know the max bit rate through these devices?
We only spec Fmax on parts that have clocks. If you look at the AUC16374 you can see that at 2.5V the FMAX will be 250Mhz. This should be the same for all AUC parts.
However, the AVC32T245 does specifiy bit rate. Why is this?
And just to confirm, we can run the bus for the AUC32245 at 250MHz, or 500Mb, correct?
Yes the AUC should work fine at this frequency into the specified loads..
The data sheet of SN74AVC32T245 says that max. rising edge delay and falling edge delay (Tplh, Tphl) is more than 3ns, I am confused that how can SN74AVC32T245 reach 320Mbps speed. Could you please explain it to me?
What is the speed when SN74AUC32245 works on +1.2V?
Does SN74AUC32245 work well at 165MHz in your project ?
should be good up to 250Mhz
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