SN74LVT244B: SN74LVC8T245 max supported frequency

BX27

Part Number: SN74LVT244B
Other Parts Discussed in Thread: SN74LVC8T245

Hi, this may be a general question.

We are trying to choose a high-speed buffer (3.3V-to-3.3V) for a long JTAG Daisy-Chain which containing multiple FPGAs. the TCK signal of JTAG is approx. 66MHZ or so.

.SN74LVC8T245 and 74LVC244 are devices in our library, how could I calculate if these device could support 66MHZ ? Seems no specific frequency parameter in datasheet.

Thanks!

over 1 year ago

+1 Clemens Ladisch over 1 year ago

Guru 266310 points

At 3.3 V, LVC devices support much more than 66 MHz.

+1 BX27 over 1 year ago in reply to Clemens Ladisch

Genius 3870 points

Hi Clemens, thanks for answering.

We would like to use the deivces which is in our library if possible. May I ask how to estimate the max freq of SN74LVC8T245 and 74LVC244A when datasheet did not give this parameter? Thanks!

+1 Clemens Ladisch over 1 year ago in reply to BX27

Guru 266310 points

A safe minimum estimate can be computed from the propagation delay; for the SN74LVC8T245 at 3.3 V, this would be 1 / 6.3 ns = 158 Mbps. But this estimate usually is much lower than the actual supported frequency.

[FAQ] What is the maximum data rate (or operating frequency) for a logic gate or buffer? suggests to look at the specified maximum frequency of a flip-flop in the same logic family, but there are not translator flip-flops.

The only way to get an accurate limit is to measure it, i.e., it cannot be accurately derived from other datasheet parameters.

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SN74LVT244B: SN74LVC8T245 max supported frequency