Level Shifters??

[AA9GG]

My platform micro runs at 5v. What level shifter (5v<->3v) do you recommend for the CFAF800480E1-050SR display? The one I am currently using might be to slow. The 5v side looks fine, but the 3v side is HORRIBLE. On the SCK for example, 5v is a nice pulse train (say 10 pulses), the 3v side has a bit of noise with one BIG pulse and a few smaller ones in that time frame.

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[cosmicvoid]

74LVC4245

 

[AA9GG]

74LVC4245

I was thinking something without a direction control line, it should be transparent

 

[cosmicvoid]

I was thinking something without a direction control line, it should be transparent

So then you want something one-directional (5v -> 3v) instead of bi-directional (5v<->3v) as you indicated? In which case, what do you mean by 'transparent'? You could just use a resistive divider for one-way.

 

[AA9GG]

So then you want something one-directional (5v -> 3v) instead of bi-directional (5v<->3v) as you indicated? In which case, what do you mean by 'transparent'? You could just use a resistive divider for one-way.

I'm assuming I need 5v<->3v. I know they make bi-directional parts without a DIR line. I guess I should have said automatic rather than transparent.
I mainly need it on the 3 SPI lines, chip select and power_dwn pins.

 

[cosmicvoid]

TXB0108 or TXS0108E. The 'automatic' ones tend to be a little bit slower propagation delay. You'll have to check data sheets for that style to see if they meet your needs.

 

[AA9GG]

TXB0108 or TXS0108E. The 'automatic' ones tend to be a little bit slower propagation delay. You'll have to check data sheets for that style to see if they meet your needs.

Funny you mention those. I am actually trying to use the TXB0108. I am have a hell of a time trying to get the OE to work for some reason and that is why I was looking for other candidates. I have the pin to ground thru a resistor, like they said, but it is hit or miss. I even put the R box on it to find a value. Very strange issue. When it DOES work, the signals on both sides look BEAUTIFUL.

 

[cosmicvoid]

Does it make any difference if you drive the OE line from an unused port pin set low?

BTW, does AA9GG happen to be a call sign? I was a K8 back in the day.

 

[AA9GG]

Does it make any difference if you drive the OE line from an unused port pin set low?

OE low puts it into tri-state, that works. My first thought was to just strap it to +3v, then I saw the note about a resistor to ground which seems strange for an enable line. Apparently the pin needs to be low until power stabilizes (we a talking nanoseconds). They don't give an R value, just that it depends on the supply current.

BTW, does AA9GG happen to be a call sign? I was a K8 back in the day.

Yes, it is my Amateur Radio Callsign

 

[AA9GG]

I have found a conflict between the actual datasheet and the one for the eval board. It appears the OE pin should be connected to V+ via the resistor and NOT to ground. I also found a schematic on the 'net where it is indeed tied to V+. I will try it on Monday when I get to work...

 

[Eavy1997]

Logic signals are translated from one level to another using a level shifter. This shift typically occurs between 5V and 3.3V, but other voltages, such as 2.5V or 1.8V, can be used as needed.