KS0713 LCD driver chip

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barnacle
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Posted by barnacle: Thu. Apr 7, 2011 - 11:26 AM
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Has anyone used one of these at higher than the rated 3.3v?

Reason I ask is that I have an interface circuit talking to something that doesn't quite meet the published specs; previous 5v versions of the system work fine while 3.3v versions - constrained by this display chip - are intermittent and generally less happy.

The device manual has a change note that indicates a reduction in vmax from a previous 5.5v with no explanation, and a couple of points within whereby they suggest certain pins be kept in one state or the other if the voltage is less than 4v - which it *is now* - but doesn't say whether this is merely a characterisation to indicate everything works fine at 3.3v or a change in manufacturing that will let the magic smoke out at 5v...

I'm currently very tempted to crank up the voltage and see where smoke appears, but if anyone's tried this, it'd be nice to know!

Ta,

Neil

Neil Barnes
www.nailed-barnacle.co.uk

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Learning and Information, General Electronics
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barnacle
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Posted by barnacle: Mon. Apr 11, 2011 - 06:42 PM
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So I applied a hammer to it.

I've had one working at 4.5v all afternoon - about six hours so far - and I'm now running at 4.5v and with a display update every thirtieth of a second, writing to almost every pixel on the screen.

Let's see how it copes overnight...

Neil Barnes
www.nailed-barnacle.co.uk

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barnacle
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Posted by barnacle: Tue. Apr 12, 2011 - 05:53 AM
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...and it's still working fine in the morning.

I don't like working things outside their published specifications, but I think this is looking robust enough that it's worth trying in situ to see if this solves the primary problem.

Neil Barnes
www.nailed-barnacle.co.uk

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Plons
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Posted by Plons: Tue. Apr 12, 2011 - 12:22 PM
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Neil, I have a 5V LCD running on a Mega128 @ 3.3V, a Wiznet200 module. It runs fine :) No extra measures necessary.

Also have a 3.3V graph LCD (Philips controller) on a 5V mega8: I use a resistor divider for the communication.

If you wish to make certain your application will work fine in the field, I suggest you run the AVR @ 5.2 or 5.4V and see if that works fine overnight. If that succeeds, running the AVR @ 4.5V in the field will almost certainly work reliable.

Nard

(edited the post)

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barnacle
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Posted by barnacle: Tue. Apr 12, 2011 - 04:39 PM
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Yah... unfortunately it didn't solve my original problem. Rats.

Back to the drawing board... now why would a system which works fine at five volts work intermittently at less than that, when it's using a 12v serial signal?

Aye well, I'll solve it.

Neil Barnes
www.nailed-barnacle.co.uk

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Jepael
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Posted by Jepael: Tue. Apr 12, 2011 - 06:57 PM
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Ooh a trick question?

So running a system at 3.3V instead of 5 - would depend on a system of course.

Different voltage regulator might have something to do here.

Also crystal circuitry in chips may be somewhat voltage dependent.

Then IO pin voltages have different input thresholds too.

Well just to give some ideas. Need more?

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barnacle
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Posted by barnacle: Tue. Apr 12, 2011 - 07:36 PM
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Not a trick question... I'll start a separate thread.

Neil Barnes
www.nailed-barnacle.co.uk

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peret
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Posted by peret: Tue. Apr 12, 2011 - 08:49 PM
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CMOS speeds up a lot at increased supply voltages. The data sheet AC parameters are specified from 2.4 to 3.6 volts, but the absolute maximum VCC is 7V, so it should run quite happily at 5V with a smart increase in speed. My guess is your interface timing is marginal for 3.3V but comfortably met at 5V. I imagine the reason the VDD range was changed is not to say it won't work any more at 5V, but to give assurance that it WILL work at 3.3V.

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