SN74LVC1T45: Proper Impedance matching design for bidirectional level translator

Gavi Siddu

Part Number: SN74LVC1T45

Hi Team,

Can u suugest the impedance matching circuit compatible with the SN74LVC1T45. I have two 150R at input and output for dampening.

While measuring the output from custom board using 75ohm BNC to BNC connector i am getting the output as follows:-

8Mhz

The output is bad as frequency is getting increased. So i am suspecting the imepdance mismatching for this.

Can somebody provide any suugestion on this?

Thank you

over 4 years ago

0 Dylan Hubbard over 4 years ago

TI__Mastermind 42640 points

Hey Gavi,

150 ohms is probably overkill, 33-50 should do. I would try to measure the signal with active probes with that will have lower capacitance and should provide cleaner looking signals when measuring.

0 Gavi Siddu over 4 years ago in reply to Dylan Hubbard

Prodigy 240 points

Thank you for the reply. I will try with suggested resistor values. what about impedace matching circuit?

0 Gavi Siddu over 4 years ago in reply to Dylan Hubbard

Prodigy 240 points

Regarding the Active probes, in the end application, we use BNC to BNC cable for interfacing. Hence I am testing with BNC to BNC 75ohms cable

0 ShreyasRao over 4 years ago in reply to Gavi Siddu

TI__Guru 56070 points

the BNC cables can add upto 120pF of cap loading. If you have 10x passive probes, it would be ideal too.

0 Gavi Siddu over 4 years ago in reply to ShreyasRao

Prodigy 240 points

I did some fine tunig by adding two capacitors pulled ground at input and output(12pf and 15pf). There were some improvents in the waveform, but still some issue on the rising and falling edge of the wavefrom. I need improvemnts on the rising and falling edge of the waveform. Can u suggest anything ?