Driving 1.8v Signals

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clpalmer
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Posted by clpalmer: Fri. Dec 1, 2006 - 03:41 PM
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I'm running an AVR at 3.3 but need to control a component that uses 1.8v for I/O. I know I could run it through a level shifter, but if the signals are all unidirectional (AVR->Slave) can I just plunk in a few transistors instead?

My question is, will the transistor function ok if the Base->Collector voltage is positive? The base will have 3.3 from the AVR and the collector will be 1.8V through a pullup connected to VCC.

Is there another simple way of doing it without going to a full level shifter chip?

Clancy _________________ Step 1: RTFM Step 2: RTFF (Forums) Step 3: RTFG (Google) Step 4: Post

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AVR Microcontrollers, megaAVR and tinyAVR
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dl8dtl
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Posted by dl8dtl: Fri. Dec 1, 2006 - 04:13 PM
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> but if the signals are all unidirectional (AVR->Slave) can I
> just plunk in a few transistors instead?

That *is* your level-shifter then.

Have a look at the STK500 circuit diagrams, they've got two-transistor
level shifters for some signals.

The simplest design would obviously constitute of just a few resistors.

Jörg Wunsch

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Jepael
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Posted by Jepael: Fri. Dec 1, 2006 - 11:15 PM
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There are a few level shifting chips from Maxim. For multiple lines in a single chip, between voltage levels. Used one of these for communications between AVR and bluetooth chip, maybe. Don't remember anymore :)

- Jani

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S-Sohn
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Posted by S-Sohn: Sat. Dec 2, 2006 - 03:10 PM
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A simple bidirectional transistor level shifter is explained here:
http://www.edn.com/archives/1996/110796/23DI_02.htm

Regards
Sebastian

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sgomes
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Posted by sgomes: Sat. Dec 2, 2006 - 05:45 PM
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Clever circuit! I love clever circuits.

Go electric!
Happy electric car owner / builder

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S-Sohn
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Posted by S-Sohn: Sat. Dec 2, 2006 - 06:02 PM
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This article explains some more simple level shift techniques:
http://www.edn.com/contents/images/6335309.pdf

Regards
Sebastian

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clpalmer
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Posted by clpalmer: Sun. Dec 3, 2006 - 07:42 PM
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Thanks Sebastian =)

Clancy _________________ Step 1: RTFM Step 2: RTFF (Forums) Step 3: RTFG (Google) Step 4: Post

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RES
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Posted by RES: Mon. Dec 4, 2006 - 10:13 PM
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Electronic design has changed considerably since the days when TTL and 5V CMOS were the dominant standards for logic circuits. The increasing complexity of modern electronic systems has led to lower voltage logic, which in turn can cause incompatibility between input and output levels for the logic families within a system. It is not unusual, for example, that a digital section operating at 1.8V must communicate with an analog subsection operating at 3.3V. This article examines the basics of logic operation and considers, primarily for serial-data systems, the available methods for translating between different domains of logic voltage.

http://www.maxim-ic.com/appnotes...

RES

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