Logic level converter 5V to 0.8V

[nana_7488]

Hi

I've need help on interfacing the output 5V from counter to the input 0.8V of my fabricated chip. Would someone give ideas on how to do this without burn my chip.Thanks

 

[alexan_e]

You can use a simple voltage divider with two resistors, like 5k+1K

Alex

 

[nana_7488]

Thanks for the response. But is voltage divider works fine with the digital signal? or do I have to use logic level converter or level shifter? I do need to make it as simple as possible because I need to test my chip urgently.

 

[alexan_e]

You didn't specify anything about the signal, is it a very high frequency, does your input stage of the chip have a high impedance?
Other than that a resistive voltage divider can easily be used.

Alex

 

[nana_7488]

Hi Alex,

Just wondering, if the signal is high frequency (200MHz), so I can't use the voltage divider? Then what should I use?Thanks

 

[alexan_e]

I'm afraid I haven't used anything like that, I have only used a divider in mcu signals but I think that you have to use a divider like in an oscilloscope probe with a capacitor.

Alex

 

[seadolphine2000]

I'm afraid that a simple potential divider will not work with such high speed signal. I tried it with baud rate 115k and it slow down the connection speed.
So, I think you have to go to level converter chips.
Check this link, it might help you:
https://www.google.com/url?sa=t&source=web&cd=2&ved=0CB4QFjAB&url=http%3A%2F%2Fwww.datasheetcatalog.org%2Fdatasheet%2Fon_semiconductor%2FMC74VHC1GT50-D.PDF&rct=j&q=0.8%20logic%20level%20shifter&ei=O5EJTqb7Fc2a-waU_fDOAg&usg=AFQjCNHZDTP4KSYy3kUhC4jm7Y7knKoIpw&sig2=uRK7QLydfO--1GRkSPkPGA&cad=rja

 

[alexan_e]

I'm afraid that a simple potential divider will not work with such high speed signal. I tried it with baud rate 115k and it slow down the connection speed.

You had problems with just 115KHz?

Alex

 

[seadolphine2000]

You had problems with just 115KHz?

Alex

Yes, the TXD and RXD lines were quite unstable and I had to lower the speed to 56KHz although the GPRS module supports the 115K.

 

[alexan_e]

I find it strange, maybe it had to do with the characteristics on the TXD and RXD signals of the GPRS?
What divider did you use, was it 5v to 3v3 from mcu to GPRS in the transmit line?
And what about the signal from the GPRS to the mcu, did you connect the 3v3 to the 5v mcu?

Alex

 

[Syncopator]

Try a diode limiter.

A couple of diodes with a low Vf (germanium or Shottky) in series perhaps?

 

[umesh49]

What is your maximum frequency of operation. Is it really 200MHz?