• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

MCU voltage mis-match to LCD

Status
Not open for further replies.

Calvin Black

New Member
Hello,
Regarding Renesas part number R5F100LEAFB#V0: I have its data lines and control lines tied to an LCD (operating at 5V). The R5F100LEAFB#V0 has EVDD at 3.3 V. Will the R5F100LEAFB#V0 be damaged due to the voltage mis-match to the LCD (3.3V vs. 5V)?

Thanks,
Calvin
 

spec

Well-Known Member
Most Helpful Member
Hy Calvin,

Welcome to ETO

A 5V part driving a 3.3V part may damage the 3.3V part and, highly unlikely, may damage the 5V part.
A 3.3V part driving a 5V part will neither damage the 5V part or the 3.3V part.

To interface between logic running off different supply lines and have fully specified interoperatability you need proper level translators.

You will see two resistors being used on the net but this is not satisfactory (update: this in not the same as the approach that Ian Rogers recommends in post #3).

You will also see a FET interface used. While this is innovative it can have problems.

Level translator bi direction 8 channel TX010BE (does not have full high speed drive capability and can be problematic) http://www.gearbest.com/other-accessories/pp_227270.html

Level translator 8 channel: 74LVC8T245 http://www.ebay.co.uk/itm/8-Channel-74LVC8T245-COMS-TTL-Level-Conversion-Module-Level-Convertor-Top-/272156191676?hash=item3f5dc5ebbc:g:7QsAAOSwwpdW2UO7

Level translator 16 channel: 74LVC16T245 http://www.ebay.co.uk/itm/74LVC16T245-16-Channel-TTL-Stable-COMS-Level-Conversion-Module-Pinboard

spec

(PS: I see you are from the US. Care to tell us which state and put it next to 'Location' on your user page so that it displays in the window at the left of your posts)
 
Last edited:

Ian Rogers

User Extraordinaire
Forum Supporter
Most Helpful Member
Your ports all have switchable open drain outputs.... Therefore switch to open drain.. Fit a bussed resistor to 5v.. And it will work.

The pic32 have this.. It makes the ports 5v tolerant whilst you can still use it with 3v devices... Just ensure the ports are switched ( I think they are selected by default, but your datasheet will confirm this )
 
If all the lines going to the LCD are output only should he be fine? The only risk is 5V being applied to pins of the 3.3V device. Is he doing that? Almost nobody reads anything from a standard 2-line LCD.

What LCD are you using, Calvin?
 

Jon Wilder

Active Member
So long as he keeps the R/W pin on the LCD at 0V (write only) he should be fine as far as levels go. However, I've attempted to drive a 5V LCD from a 3.3V device. Didn't work too well on its own because the display perceived 70% Vcc as logic 1 and the 3.3V device fell just under that. So in the end I ended up having to use a logic level translator circuit between the two.
 

Calvin Black

New Member
Thank you all for your information. I think I'll implement a level translator.
By the way, for the LCD I'm planning to use TC1602A-09T from Adafruit.

Thanks!
 

spec

Well-Known Member
Most Helpful Member
Let us know how it goes. The net is full of people who have had troubles interfacing 3.3V and 5V systems.:eek:

spec
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top