DS90LV048A: Not getting Proper output voltage 3.3v and sometime go in Negative Range

VISHAL KALWANI

Intellectual 705 points

Part Number: DS90LV048A
Other Parts Discussed in Thread: SN74LVT125, DS25BR100

I am not Getting output 3.3v.

But goes in Range of 4V to 5V and goes in negative range too.

i have connect output of cmos signal connected to current sink ic input.

I have attached schematic and output waveform.

over 6 years ago

0 Yaser Ibrahim over 6 years ago

TI__Genius 10250 points

Hello,

It should give around 3.3V, but may be less depending on the load. You seem to have some overshoot and undershoot which makes the peak-to-peak value higher. This may be due to the load it is connected to, including the scope probe. Have tried to look at the signal without load?

Regards,
Yaser

0 VISHAL KALWANI over 6 years ago in reply to Yaser Ibrahim

Intellectual 705 points

This waveform where without load only.

0 Yaser Ibrahim over 6 years ago in reply to VISHAL KALWANI

TI__Genius 10250 points

Hello,

What is the "current sink ic" you mentioned earlier? What are the characteristics of its input?
This also could be related to the setup itself (probe, scope, connections...). Can you please double check the setup and perhaps try other probes? Please provide all the details of the setup. Thanks.

Regards,
Yaser

0 VISHAL KALWANI over 6 years ago in reply to Yaser Ibrahim

Intellectual 705 points

Yes current sink ic is SN74LVT125.I have connect the output of DS90LV048A TO SN74LVT125.AND SN74LVT125 INPUT CHARACTERISTICS IS SAME AS OUT WAVE FORM AS I HAVE ATTACHED PREVIOUS.

0 Yaser Ibrahim over 6 years ago in reply to VISHAL KALWANI

TI__Genius 10250 points

Hello,

The input impedance of the load (sink IC) is very high, and depending on what you do for termination and how long is the distance, you may be getting reflections. Please note that the rise/fall times at the output of DS90LV048A are very fast (~1 ns). How long is the distance to the load?

Regards,
Yaser

0 VISHAL KALWANI over 6 years ago in reply to Yaser Ibrahim

Intellectual 705 points

Sink ic is place very near to DS90LV048A.

0 Yaser Ibrahim over 6 years ago in reply to VISHAL KALWANI

TI__Genius 10250 points

Hello,

If that is the case, then there is a good chance this may be a measurement setup issue (probe/cable, scope termination, ...) . Can you please double check the setup? Also, please provide all the details of the setup. Thanks.

Regards,
Yaser

0 Yaser Ibrahim over 6 years ago in reply to Yaser Ibrahim

TI__Genius 10250 points

Hello,

I haven't heard from you for a while. Were you able to resolve the issue? I will close this thread, but if you still need support, feel free to reply and it will get open again.

Regards,
Yaser

0 VISHAL KALWANI over 6 years ago in reply to Yaser Ibrahim

Intellectual 705 points

I am getting overshoot and undershoot with load and without load.

I have connect 1.8mA load.

I Have remove current sink IC.

0 Yaser Ibrahim over 6 years ago in reply to VISHAL KALWANI

TI__Genius 10250 points

Hello,

Please give us full details of your setup. What is exactly connected to the output, including probes, input impedance of scope, ...etc. How long are the cables,= and traces. Are there connectors along the way?

Regards,

Yaser

0 VISHAL KALWANI over 6 years ago in reply to Yaser Ibrahim

Intellectual 705 points

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

3.9pF is capacitor of probe.Impedance of probe 10Mohm.

I have attached the pic of set up.

Trace length from connector to DS25BR100(BUFFER) is 1536mils.

Trace length from DS25BR100(BUFFER) to DS90LV048A is 1641mils.

CABLE USED UNSHIELDED TWISTED PAIR CABLE Between connector to connector of 1 Meter long.

I have tested between the Frequency of 10Mhz to 100Mhz.

But every time giving me undershoot and overshoot with and without load.

0 VISHAL KALWANI over 6 years ago in reply to VISHAL KALWANI

Intellectual 705 points

cat 6 cable is used between connector to connector.

0 VISHAL KALWANI over 6 years ago in reply to Yaser Ibrahim

Intellectual 705 points

Hey Yaser

I have given reply on June 22.

But did not Received any Response from your side till now.

0 Yaser Ibrahim over 6 years ago in reply to VISHAL KALWANI

TI__Genius 10250 points

Hello Vishal,

Sorry for the late reply, but June 22 is Saturday!

The cause of the overshoot is most likely still impedance mismatch. The output impedance of the DS90LV048A is low (20-30 Ω). If the trace characteristic impedance is 50 Ω then you could try to add a series resistor of ~25 Ω at the outputs of DS90LV048A.

Regards,

Yaser

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DS90LV048A: Not getting Proper output voltage 3.3v and sometime go in Negative Range