[AVR] 74HCT541 to translate 5V logic to 3.3V logic

[sreepss]

Shall we use 74HCT541 to translate from a 5V logic to 3.3 logic? I mean from a 5V processor lines to a 3.3V display lines?

I have tried this, but a 3.3V powered HCT 541 gives wrong output (4.1 V) and disturbing the 3.3V supply rail. :roll:

here's my schematic

 

[andre_luis]

You are simulating with the 74HCT541 ( 4.5v-5.5v ), but should use the 74HC541 ( 2.0v-5.5v ) instead. Anyway, according to datasheet the maximum allowed input is VCC.

 

[KlausST]

Hi,

What's the idea behind using a HCT device? I can't see it.

Use a AHC device, but supplied with 3.3V.
Then the output is 0V/3.3V....while the input may be higher than it's supply voltage.

Klaus

 

[sreepss]

thanks for the replays,

Negative Negative



I have actually used HC541 not HCT. Sorry for the mistake whenever I give the input to the buffer from a 5V ATMEGA port, the output goes beyond (4.1V the HCT's VCC( 3.3V ) and the 3.3V power rail raised by 4.1V.

 

[KlausST]

Hi,

from a 5V ATMEGA port,

May I ask why you don't use 3.3V supply for the Atmega?

Klaus

 

[sreepss]

hi KlaussT,

I have already running design of ATMEGA with 16MHz clock. I need to run it with 8MHz for 3.3V design. currently I cannot change the design

 

[KlausST]

Hi,

Again: use AHC, supplied with 3V3.
HC are not 5V input tolerant with 3V3 supply.

Klaus

 

[sreepss]

Hi there.. Did you mean 74AHC541?

 

[KlausST]

Hi,

Any AHC family member has this 5V tolerant inputs.
If you need 541 functionality... then

Yes, use 74AHC541.

Klaus

 

[sreepss]

Thanks for the replay. I will try with AHC