SN74LVT125: what is frequency Range of SN74LVT125?

VISHAL KALWANI

Intellectual 705 points

Part Number: SN74LVT125
Other Parts Discussed in Thread: SN74LVC125A

Can I apply 100Mhz square wave signal input to SN74LVT125?

I have apply 100Mhz signal with no load it was giving Sinewave of 3.3v Around.

But when I connect 5mA load signal attenuate.That is one pulse is high and other is low.

over 5 years ago

0 Clemens Ladisch over 5 years ago

Guru 276440 points

Are the oscilloscope probes ×1 or ×10?

How much is the capacitive load on the output (including the probe)?

0 VISHAL KALWANI over 5 years ago in reply to Clemens Ladisch

Intellectual 705 points

Oscilloscope probe is 10x. oscilloscope probe part number-TPP0500B

3.9pF is capacitor of probe.

in output i have connect 10mA electronic load.

some portion goes in negative around 1v in second pulse as you can see in image.

0 Emrys Maier over 5 years ago in reply to VISHAL KALWANI

TI__Guru* 96752 points

Hi Vishal,

What exactly is the "10mA electronic load" that you are connecting to the device? And what's the method for connecting it? I've seen simliar tests connected via transmission lines (RG-58) that caused significant signal integrity problems due to the added capacitance.

The best method for measuring this is with a differential probe, however the probe you mentioned should show a clean signal.

The test conditions for timing tests is shown in the "PARAMETER MEASUREMENT INFORMATION" section of the datasheet -- in this case, a 500 ohm + 50pF load.

0 VISHAL KALWANI over 5 years ago in reply to Emrys Maier

Intellectual 705 points

Why 100Mhz is going 0.5v negative and I have give square wave of 5nns on and off, then why it is showing sinewave.

I have connect 20mA load through 165E register.And one end of register is connect to cmos output pin and other to ground.

Please provide solution to this problem.

0 VISHAL KALWANI over 5 years ago in reply to VISHAL KALWANI

Intellectual 705 points

why 100Mhz signal going negative 0.5v?

it is configured 5ns on and off with square wave is apply thenn why sinewave appear at output.

0 Emrys Maier over 5 years ago in reply to VISHAL KALWANI

TI__Guru* 96752 points

It sounds like the load you are attaching is complex and is causing issues.

0 VISHAL KALWANI over 5 years ago in reply to Emrys Maier

Intellectual 705 points

I have attached the waveform without load.

You can see image below.

It is going 900mV down at 100 Mhz.

So now what should i do?

or else suggest what should i try?

I have also try with your circuit as you have suggest of PARAMETER MEASUREMENT INFORMATION but i am getting worst result from that.

0 Emrys Maier over 5 years ago in reply to VISHAL KALWANI

TI__Guru* 96752 points

Hi Vishal,

I'm not sure what you're expecting to see at this frequency, but that's a pretty typical waveform for a 100 MHz logic buffer, especially when operating below nominal voltage. Overshoot/undershoot is normal with light loads from a strong driver. If you slow down your signal, I'm sure you will be able to see the edge rates remain the same and the ringing dies off relatively quickly.

0 VISHAL KALWANI over 5 years ago in reply to Emrys Maier

Intellectual 705 points

Does SN74LVT125 at 3.3V support 100Mhz?

In Data sheet it is not specified.

0 Dylan Hubbard over 5 years ago in reply to VISHAL KALWANI

TI__Mastermind 44630 points

Hi Vishal,

As you have stated, the data rate is not specified. 100 MHz may be tough to achieve with the device. I also recommend checking out the SN74LVC125A for this application as it should be able handle this frequency. However, the load also plays a big part in the data rate you can achieve as you have seen(especially when you start reaching these high frequencies). This means even PCB parasitics can also impact it.

I recommend picking up an EVM found here and running the test with nothing but the signal generator and scope probes. If you can't get the desired output waveform at the desired frequency then you most likely won't with the device in your system. If you do get the results you want, I would then add the expected load the device would have in the system and re-run the tests.

0 VISHAL KALWANI over 5 years ago in reply to Dylan Hubbard

Intellectual 705 points

I have tested with 5mA,10mA and 19mA load. But I have found that 0.5v goes in negative.

I have also check the datasheet of SN74LVC125A but inn that also they have tested with 10Mhz.Not 100MhZ.

0 VISHAL KALWANI over 5 years ago in reply to Dylan Hubbard

Intellectual 705 points

∆t/∆v Input transition rise or fall rate is any relation with Frequency?

Using this can i find Frequency?

0 Clemens Ladisch over 5 years ago in reply to VISHAL KALWANI

Guru 276440 points

The allowed input transition rate depends only on the supply voltage, and has nothing to do with the output frequency it is capable of.

0 VISHAL KALWANI over 5 years ago in reply to Clemens Ladisch

Intellectual 705 points

From Input transition rate I have find Rise time.

And from Rise time I have find Frequency.

Please Refer The equation specified in Ti app note.

And the Ic you have specified is also not able to work at 100Mhz.

You

dt/dv = tRF/(0.9 × Vcc) - (0.1 × VCC)

http://www.ti.com/lit/wp/slla364a/slla364a.pdf

For Frequency

Tr = 1/f*π

0 Dylan Hubbard over 5 years ago in reply to VISHAL KALWANI

TI__Mastermind 44630 points

Hi Vishal,

As Clemens stated, the input transition rate spec doesn't relate to the output frequency. However, the output transition is related to the max frequency. For example, a 100 MHz square wave with a period of 10 ns can't be achieved if the output has a rise time of 7 ns. We have a FAQ that covers output transition below:

https://e2e.ti.com/support/logic/f/151/t/718814?tisearch=e2e-sitesearch&keymatch=faq%3Atrue

0 VISHAL KALWANI over 5 years ago in reply to Dylan Hubbard

Intellectual 705 points

you have specified Ic SN74LVC125A.

I have calculated tlh and thl as you have specified in FAQ

I have considered load capacitance of 30pF.

tlh=1.9ns

thl=1.375ns

so transition time is 1.9ns.

so how it can support 100Mhz?If take 10% of period of 100Mhz of it we can get rise time of 1ns.

0 VISHAL KALWANI over 5 years ago in reply to Dylan Hubbard

Intellectual 705 points

Is there is any relation between rise time,minimum pulse width and slew rate and transition time.

0 Emrys Maier over 5 years ago in reply to VISHAL KALWANI

TI__Guru* 96752 points

Hi Vishal,

I don't understand the question... you want to know if any of those 4 things are related? What are you trying to determine?

Logic

Logic forum

SN74LVT125: what is frequency Range of SN74LVT125?