LMK00105: Ringing observed on the negative edge of the output

Nithin Shivalingappa

Prodigy 10 points

Part Number: LMK00105

Input to LMK00105 is a 1Hz single ended signal with 50% duty cycle.

The preferred config (Figure 6 in datasheet) is used in our design.

At the output, a 17usec pulse is observed with ringing seen on the negative edge of the pulse.

Because of the ringing, false triggering is happening at the negative edge.

Why is the ringing seen only on the negative edge?

How do I overcome this ringing on the negative edge ?

over 3 years ago

0 Jennifer Bernal over 3 years ago

TI__Genius 16485 points

Hi Nithin,

1) Can you share a waveform image of the input and output?

2) Does this occur at all the outputs of the LMK00105?

There may be a termination mismatch causing the reflection at the output. You could try changing the Rs value to ensure a 50 ohm transmission line.

Regards,

Jennifer

0 Nithin Shivalingappa over 3 years ago in reply to Jennifer Bernal

Prodigy 10 points

Hi,

Yes. The issue is seen on all outputs of LMK00105.

Waveforms attached.

0 Jennifer Bernal over 3 years ago in reply to Nithin Shivalingappa

TI__Genius 16485 points

Hi Nithin,

This actually looks like it could be noise in the power supply. Try measuring the VCC pin as well to see if you get similar distortion and also adding a 1uF cap near VCC.

Regards,

Jennifer

0 Nithin Shivalingappa over 3 years ago in reply to Jennifer Bernal

Prodigy 10 points

Yes. There was noise on VDD during the neg edge of the clock.

After adding 1uF to the existing 22u+1uF, it reduced, but is not eliminated completely.

The problem is still there.

Also, why the duty cycle of the output changed in the original case ?

0 Jennifer Bernal over 3 years ago in reply to Nithin Shivalingappa

TI__Genius 16485 points

Hi Nithin,

Noise in the VDD pin is the main culprit. This would affect the duty cycle and cause glitches as you've observed. You would have to adjust your supply to ensure the glitch is removed.

Regards,

Jennifer

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LMK00105: Ringing observed on the negative edge of the output