I/O Buffers in Board desing

[samsunil]

Hello,

We have different kind of I/O buffer technologies available today. (Ex: LVCOMS , LVTTL and SSTL)

I would like to know when do we really need buffer ?

Scenario

1. I have a open drain output driving 3 devices ? Do i need buffer here ?
2. I have a push-Pull output driving 3 devices ? Do i need buffer here ?

Regards
Antony

 

[ronsimpson]

You have really not give us much information.
If the 3 devices are on another board, thin probably a buffer, or a long distance away.
Most times I would not use a buffer.

 

[samsunil]

Hi Simpsion,

Thanks for responding

All the 3 devices are placed in a single PCB with less than 3 inches away from the driver.
I would like to know how we need to select a buffer for different I/O technologies (LVCMOS or LVTTL)
Different I/O technologies means different drive strength , How we need select the right buffer just in case if we need one in our design.

Regards
Antony

 

[ronsimpson]

First: There are different supply voltages. Some parts are 5 volt only. Some are 3.3V or 2.5V or 1.8 etc. (there is also a 12V type)
When you see "LV" that is likely Low Voltage. See data sheet. Some devices can run form 3.0 to 5V.
If you have one device on 5V and another on 1.8V then you will need a Level Translator Buffer.
Each type of device sees a 0 or a 1 at different levels. Typically CMOS 0=the bottom 1/3 of supply and 1=the top 1/3 of supply. While 1/3 to 2/3 voltage is unknown. TTL has a very different 1 and 0 levels. It is best to keep all the parts to the same type. (or watch out for problems)
There is a CMOSTTL type which is CMOS but the input buffer has been changed to work more like TTL.

 

[samsunil]

Thanks !!