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SN74AXC1T45: Level shifter for 62.5MHz

Mayank Mishra
Prodigy 470 points
Part Number: SN74AXC1T45
Other Parts Discussed in Thread: 74AVC1T45

Hi Team,

Our customer need a level shifter IC to level shift 1.8V level single ended clock signal to 0.8V level clock signal. The clock signal frequency is 62.5MHz.

 

They have shortlisted following devices. Please find the use case and queries in below table:

Can you please help with the same.

Sr.No.

Part Number

Use Case

Propagation delay (tpd)

Supported Freq = 1/tpd

Query

1

SN74LVC1G07DCK

VCC = 1.8V and
Open drain output Pulled up to 0.8V

tpd (min) = 2.4 ns
tpd (max) = 8.3 ns

Freq (max) = 416.66 MHz
Freq (Min) = 120.48 MHz

Is it ok to use open drain buffer for clock signal level translation ?

2

SN74AXC1T45

VCCA = 1.8V , VCCB = 0.8V

tpd (min) = 0.5 ns
tpd (typ) = ??? Not given
tpd (max) = 41 ns

Freq (max) = 2 GHz
Freq (Typ) = ???
Freq (Min) = 24.39 MHz

This device supports Up and Down Translation Across 0.65 V to 3.6 V hence we are thinking of using this device preferably.

But as typical value is not known, we are not sure whether this will work for 62.5MHz or not ? Please confirm.

3

74AVC1T45

VCCA = 1.8V , VCCB = 0.8V

tpd = 12.2 ns

81.96 MHz

This device support Down Translation to 0.8 V which is at boundary hence there is no scope of margining below if required.
  • 0
    TI__Mastermind 44470 points

    Hey Mayank,

    I would have to recommend the SN74AXC1T45 as it has a supply range that meets your needs and it will be the fastest of the 3. Just a note, using 1/Tpd isn't a good way to estimate the maximum operating frequency. For example, the AXC device will not reach anywhere near 2 GHz. Reason for this is the output driver limitations. It would be better to figure out the estimated rise time with the expected capacitive load (this will also limit the max frequency). The rise time will tell you what frequency may be achieved since you would typically want a rise time no more than a third of the bit width to maintain good signal integrity. This FAQ will help with the estimation, but I think the 62.5 MHz will be achievable by the AXC device.