Author Topic: MSP430G2 on 5V  (Read 3082 times)

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Offline brainwashTopic starter

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MSP430G2 on 5V
« on: March 13, 2013, 07:47:54 pm »
Ok ok, I know, it is bad, do not use in commercial designs, bla bla.

I know that VCC is clamped by diodes so it's not a huge problem feeding it 5V through a limiting resistor. I can also go with a voltage divider.
What about I/O pins? There's no electrical schematic of them, just some block diagram. Can these manage 5V via a 10k-60k resistor?

I'm out of PIC10F so I have to use the lowest thing I have on hand, otherwise I have to break out the mid-range PICs and it would be a waste for a 3 GPIO project.
 

Offline SebG

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Re: MSP430G2 on 5V
« Reply #1 on: March 13, 2013, 08:09:36 pm »
Hey.
I'm not familiar with TI MCUs but from the data sheet the absolute maximum voltage that can be applied is 4.1V so maybe consider using 1 or 2 diodes in series with the power pin of the MCU since they can step down the voltage from 5V to 5 - (2* 0.6) = 3.8V or so.  Resistors might not ensure the voltage drop is constant which depends on what the MCU is doing or how much current it is drawing.  If using resistors then consider what is the minimum and maximum current the MCU will draw (this will create a Voltage-drop across the resistor) then you need to compare the voltage with the minimum and maximum voltage the device can operate on.
Sebastian
 

Offline brainwashTopic starter

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Re: MSP430G2 on 5V
« Reply #2 on: March 13, 2013, 08:17:13 pm »
There are a lot of good ways to do it: voltage divider, transistor, ULN buffer, ....
I just want to do it the bad way and wondered if anyone has tried feeding these chips with with <2mA @ >4.2V .
Well, I guess I just have to try it and see, it's not like I have much use for these low-power chips.
 

Offline mrflibble

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Re: MSP430G2 on 5V
« Reply #3 on: March 13, 2013, 08:18:54 pm »
Is there any IBIS data out there for the MSP430G2? That should get you some idea of what those clamping diodes will take, and what they won't take. Mostly it's just ... slap on a current limiting resistor so the clamped voltage at the msp's io pads slay within acceptable limits.
 

Offline brainwashTopic starter

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Re: MSP430G2 on 5V
« Reply #4 on: March 13, 2013, 08:23:12 pm »
What's IBIS data?

Somewhere in the messy datasheet it says Absolute maximum ratings: Diode current at any device pin +-2mA. I assume that should be the clamping diodes, but as a rant that's one of the worst uC datasheet I have ever seen.
It didn't stop half of the world to embed the chips in their designs though.
 

Offline mrflibble

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Re: MSP430G2 on 5V
« Reply #5 on: March 13, 2013, 08:57:40 pm »
Based on this thread I think no IBIS for msp430. :P

Also note this response:

Quote

One reason to create IBIS for the MSP430 would be to assist in determining the required input protection circuitry.

IBIS helps because it shows the I-V curve for the protection diodes as you go above VDD and below VSS.

Spec says you need to limit current to < 2mA,  so if you're switching a 12V input you need to factor this into the voltage divider.

So now you know why I suggested ibis data. ;)
 


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