SN74AVC4T245: abnormal waveform

Che Wen Yeh

Intellectual 960 points

Part Number: SN74AVC4T245

Tool/software:

Hi Teams,

We find there are step waveform on slaver side, but there is normal waveform on master side.

Please refer schematic and waveform as following, thanks.

before level shift :

after level shift:

1 month ago

0 Clemens Ladisch 1 month ago

Guru 317450 points

How long are the traces between the level shifter and the slave device? What is their characteristic impedance? What is the distance between the level shifter and the three source termination resistors?

Do the waveforms become better or worse if you use 22 Ω instead?

0 Che Wen Yeh 1 month ago in reply to Clemens Ladisch

Intellectual 960 points

Hi Clemens,

Reply as following, thanks.

1. How long are the traces between the level shifter and the slave device?
Total about 4800mils.
2. What is their characteristic impedance?
50ohm
3. What is the distance between the level shifter and the three source termination resistors?
Level shifter to master side termination resistor is about 1100mils , to slaver side termination resistor is about 150mils.
4. Do the waveforms become better or worse if you use 22 Ω instead?
Yes , I have tried to change 10ohm resistor to 22/50/100ohm, waveform changed better. Till to 100ohm , there is no this step noise.