Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

what circuit should I use for the interface between 3.3v LVTTL and 2.5V LVTTL?

Status
Not open for further replies.

daraemon_liu

Junior Member level 1
Joined
Sep 4, 2010
Messages
15
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Location
CHN,SZ
Activity points
1,394
Recently in my project I need to design a JTAG chain which contains two diffenent voltage powered JTAG I/Os,one is 3.3V LVTTL,the other is 2.5V LVTTL.
The chain can be seen in the attachment,the JATG scanner itself is powered by 3.3V.So it surely can connect to the first chip in this chain.But the second chip needs to be considered carefully.Does the 3.3V LVTTL output make overshoot in the signal for the 2.5V LVTTL input ?Can it damage the second chip? If so, what circuit should I use to avoid it? Dose the 2.5V LVTTL output meet the VIH for the JATG scanner?
TKS for your advices
 

Attachments

  • JTAG_CHAIN.bmp
    627.1 KB · Views: 89

Since we don't want to add chip any more in our board, can I try approaches as below:
For the 3.3v lvttl to 2.5v lvttl ,can I use the divider resistor to attenuate the amplitude of 3.3V output to avoid damaging?
For the 2.5v lvttl to 3.3v lvttl ,can I place a pull-up resistor to 3.3V on the 2.5V output to improve the margin above the 3.3V VIH?
 

For the 3.3V to 2.5V, a simple potential divider will do the trick. For the reverse path (2.5V to 3.3V), I'm not sure but, I think it should work.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top