POSITIVE TO NEGATIVE LEVEL SHIFTERS

Premsagar Kittur

Other Parts Discussed in Thread: SN65LVDS1, SN74LVC1G14, SN74AUP1G14

Hello,

I am looking for a level shifter that converts 0-3V pulse input to +2V to -2V output swing. This pulse switches at a frequency ~1MHz to 100MHz. But our duty cycle is very small ~2% of 1MHz - 100MHz. We are fine selecting any one frequency between 1MHz-100MHz depending on the availability of the level shifter. Let me know if there are any level shifters available.

Also, let me also know if there are any level shifters close to this specs.

over 7 years ago

0 Emrys Maier over 7 years ago

TI__Guru* 96862 points

Hi Premsagar,

I'm afraid that there aren't any parts in TI's logic portfolio that do this directly -- what you're describing is a differential transmitter. I have seen some LVDS transmitters in other groups at TI, but never one with such a large output voltage swing. One example would be the SN65LVDS1.

I do know of a circuit that could do what you want. You might take a look at it as a possibility:

0 Premsagar Kittur over 7 years ago in reply to Emrys Maier

Intellectual 255 points

But data sheet for SN74LVC1G14 says max negative voltage on any pin is -0.5V. Is it fine if we apply -2V?

Also, the data sheet does not talk about the duty cycle limit. Our spec is to achieve 2% duty cycle of say 10MHz. Can you comment on that?

0 Emrys Maier over 7 years ago in reply to Premsagar Kittur

TI__Guru* 96862 points

If the ground pin is connected to -2V, then the input is at -2V, the part sees that as zero difference. The datasheet values are referenced to the ground pin.

0 Premsagar Kittur over 7 years ago in reply to Emrys Maier

Intellectual 255 points

Sure. Thank you!
What about the duty cycle? I could not see any thing on that in the data sheet. Will it switch if the duty cycle is 2% of 10MHz?

0 Emrys Maier over 7 years ago in reply to Premsagar Kittur

TI__Guru* 96862 points

2% duty cycle at 10MHz means about a 500 MHz operation -- most logic devices can only handle ~100Mhz, so it's unlikely it will be able to drive the output cleanly at that rate. Unfortunately I do not know of a device that can handle that kind of speed. You might try building the output stage from RF transistors.

0 Premsagar Kittur over 7 years ago in reply to Emrys Maier

Intellectual 255 points

Then we can select 2MHz as the operating Fq which means 2% duty cycle is 100MHz. We are using this for Buck converter application. Also, our output load for this IC is not so high as mentioned in the data sheet. Our output load is ~5pF. Hence I believe we should be able to operate it at higher fq. Please do confirm this.

0 Michael J Schultis over 7 years ago in reply to Premsagar Kittur

TI__Mastermind 24885 points

Hello,

Yes, in theory 100MHz signal should work, but it may not be the cleanest. With only 5pF load and a short output trace you will have much better luck, but it still may not be perfect. If you could even go down to 1 MHz to get the pulse at 50MHz that would be much better.
At this point, however, it will really depend on the operating environment as well as your tolerance for the signal integrity.
Bench testing will be the best way to determine if it will work well in your system.

Best,
Michael

0 Premsagar Kittur over 7 years ago in reply to Michael J Schultis

Intellectual 255 points

Sure. Thank you very much!

0 Michael J Schultis over 7 years ago in reply to Premsagar Kittur

TI__Mastermind 24885 points

Happy to help!

Michael

0 Premsagar Kittur over 7 years ago in reply to Michael J Schultis

Intellectual 255 points

Our research project demands this chip (SN74LVC1G14) to be bare die format. Is it possible for us to get this chip bare die?

0 Michael J Schultis over 7 years ago in reply to Premsagar Kittur

TI__Mastermind 24885 points

Hello,

Unfortunately, we do not have this device readily available as a bare die.
While I am not sure exactly why you need a bare die, I wonder if one of the DSBGA devices will work for you.
For these devices, the die is essentially acting as the package for the device and the bond pads of the die are available through balls that are on the bottom of the device.
Would either the YZP or YZV package work for you?

Best,
MIchael

0 Premsagar Kittur over 7 years ago in reply to Michael J Schultis

Intellectual 255 points

Our project focuses on scaling down the package. I think YZP package works for us. I will get back to you soon on the same.

0 Michael J Schultis over 7 years ago in reply to Premsagar Kittur

TI__Mastermind 24885 points

Happy to help!

0 Premsagar Kittur over 7 years ago in reply to Michael J Schultis

Intellectual 255 points

We are planing to go with YZP package. We have following questions:

1) What kind of NMOS do you suggest us to use?

2) If load cap is around 2-3pF, do you have any idea on the power consumption of this IC (SN74LVC1G14)? In the data sheet its mentioned as low power, I just wanted to know the numbers for the above mentioned load caps.

3) What is the difference between YZP and YZV packaging? Is there any advantage of YZV over YZP because there are only 4 pins compared to 5?

Let us know which packaging has least parasitics.

Thank You!

0 Emrys Maier over 7 years ago in reply to Premsagar Kittur

TI__Guru* 96862 points

1) That's a PMOS, and I'm afraid I can't suggest one since TI doesn't make discrete ones and I am far from an expert on discrete MOSFETs. I would recommend selecting one that will support your speed requirements and has the smallest parasitics available.

2) Power consumption is a fairly complex question. If this is your primary concern, I might recommend switching to the SN74AUP1G14 since it was designed specifically for minimum power consumption. The power used can be calculated using these equations:

3) These two packages are based on the same WCSP technology and are very similar. I would recommend using the 4 pin YZV unless you have some reason to use the 5 pin YZP since it is more space efficient.

You can see the parasitic differences in the IBIS model available on our website. I have grabbed a screenshot of the pertinent section for you.

0 Premsagar Kittur over 7 years ago in reply to Emrys Maier

Intellectual 255 points

Sure. This info was really helpful. I think we will order this IC with YZV package (SN74LVC1G14YZVR) . I will get back to you if I have some more questions.

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POSITIVE TO NEGATIVE LEVEL SHIFTERS