Forums

F169 ADC series resistor question?

Started by edwinh247 October 17, 2004
I am planning on using the ADC on a 169 to monitor several voltages
that I will be using, and I was wonder what size series resistor do
you guys recommend using?

Also do yall protect your basic I/O with resistors?

I attended last years ATC and they did some demonstrations of the
output to a LCD with and without resistors, and who static discharge
effected the lines without resistors.

My need is more incase something shorts and I need to limit the current.

Any suggestions are appreciated.

Thanks,
Edwin




Beginning Microcontrollers with the MSP430

Where I have really critical stuff, in an environment that is hostile, 
or where there is the possibility of human contact I not only add 
current limit resistors where feasible, I also add active clamps, such 
as the SP720AB. This is a Harris part, now Intersil IIRC, but is 
discontinued. I still have a couple of thousand of them. It was a 16 pin 
device with 14 active clamping arrays. The SP724 is current, but has 
fewer arrays per package, so is slightly more expensive per clamp.

Al

edwinh247 wrote:
> 
> I am planning on using the ADC on a 169 to monitor several voltages
> that I will be using, and I was wonder what size series resistor do
> you guys recommend using?
> 
> Also do yall protect your basic I/O with resistors?
> 
> I attended last years ATC and they did some demonstrations of the
> output to a LCD with and without resistors, and who static discharge
> effected the lines without resistors.
> 
> My need is more incase something shorts and I need to limit the current.
> 
> Any suggestions are appreciated.
> 
> Thanks,
> Edwin
> 
> 
> 
> 
> 
> 
> .
> 
>  
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 
> 
> 


--- In msp430@msp4..., onestone <onestone@b...> wrote:
> Where I have really critical stuff, in an
environment that is hostile, 
> or where there is the possibility of human contact I not only add 
> current limit resistors where feasible, I also add active clamps, such 
> as the SP720AB. This is a Harris part, now Intersil IIRC, but is 
> discontinued. I still have a couple of thousand of them. It was a 16
pin 
> device with 14 active clamping arrays. The SP724
is current, but has 
> fewer arrays per package, so is slightly more expensive per clamp.
> 
> Al
> 

I downloaded the pdf of the 720, but at this time I just plan on using
passives.

What resistors do you recommend on the lines for input to the ADC from
supply voltage lines, such as Batteries, 3.3V, 5V, and others?  What
is the best way to determine the valve of the resistor?  Or is the
valve just determined from experience, such as a rule of thumb?

Thanks,
Edwin




> What resistors do you recommend on the lines for input to the ADC from
> supply voltage lines, such as Batteries, 3.3V, 5V,
and others?  What
> is the best way to determine the valve of the resistor?  Or is the
> valve just determined from experience, such as a rule of thumb?
>
> Thanks,
> Edwin

If you don'y need much precision, then something to limit the current thru
the on chip clamp diodes would suffice.
If you start throwing in higher value resistors, you need to take your
sampling
time into account. (This is well covered in user' guide).
Basically you want the ADC input to "see" an impedance that meets the
RC time constant requirement for your given sampling time.
If you sample too long, you will screw up the ADC reading.
If you sample too short (ie. in comparison to the TC for the ADC input ckt.
the cap won't charge to the right voltage, and your ADC readings will be
wrong
more and more as the to-be-measured ADC input voltage is higher....

-- Kris


Al,

The SP720AB and others were purchased by Littlefuse

Littlefuse shows them as active parts

This link shows the parts:

http://www.littelfuse.com/cgi-bin/r.cgi/prod_parts.html?LFSESSION=qHisgi
IqfY&PartID210

-----Original Message-----
From: onestone [mailto:onestone@ones...] 
Sent: Sunday, October 17, 2004 11:35 PM
To: msp430@msp4...
Subject: Re: [msp430] F169 ADC series resistor question?


Where I have really critical stuff, in an environment that is hostile, 
or where there is the possibility of human contact I not only add 
current limit resistors where feasible, I also add active clamps, such 
as the SP720AB. This is a Harris part, now Intersil IIRC, but is 
discontinued. I still have a couple of thousand of them. It was a 16 pin

device with 14 active clamping arrays. The SP724 is current, but has 
fewer arrays per package, so is slightly more expensive per clamp.

Al

edwinh247 wrote:
> 
> I am planning on using the ADC on a 169 to monitor several voltages
> that I will be using, and I was wonder what size series resistor do
> you guys recommend using?
> 
> Also do yall protect your basic I/O with resistors?
> 
> I attended last years ATC and they did some demonstrations of the
> output to a LCD with and without resistors, and who static discharge
> effected the lines without resistors.
> 
> My need is more incase something shorts and I need to limit the
current.
> 
> Any suggestions are appreciated.
> 
> Thanks,
> Edwin
> 
> 
> 
> 
> 
> 
> .
> 
>  
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 
> 
> 




.

 
Yahoo! Groups Links



 






Thanks for that. I did try chasing them down for a client some time ago, 
but ended up selling them a couple of my tubes. At that time I only 
found the SP724 as an available product.

Al

Leonard Braun wrote:

> Al,
> 
> The SP720AB and others were purchased by Littlefuse
> 
> Littlefuse shows them as active parts
> 
> This link shows the parts:
> 
> http://www.littelfuse.com/cgi-bin/r.cgi/prod_parts.html?LFSESSION=qHisgi
> IqfY&PartID210
> 
> -----Original Message-----
> From: onestone [mailto:onestone@ones...] 
> Sent: Sunday, October 17, 2004 11:35 PM
> To: msp430@msp4...
> Subject: Re: [msp430] F169 ADC series resistor question?
> 
> 
> Where I have really critical stuff, in an environment that is hostile, 
> or where there is the possibility of human contact I not only add 
> current limit resistors where feasible, I also add active clamps, such 
> as the SP720AB. This is a Harris part, now Intersil IIRC, but is 
> discontinued. I still have a couple of thousand of them. It was a 16 pin
> 
> device with 14 active clamping arrays. The SP724 is current, but has 
> fewer arrays per package, so is slightly more expensive per clamp.
> 
> Al
> 
> edwinh247 wrote:
> 
>>I am planning on using the ADC on a 169 to monitor several voltages
>>that I will be using, and I was wonder what size series resistor do
>>you guys recommend using?
>>
>>Also do yall protect your basic I/O with resistors?
>>
>>I attended last years ATC and they did some demonstrations of the
>>output to a LCD with and without resistors, and who static discharge
>>effected the lines without resistors.
>>
>>My need is more incase something shorts and I need to limit the
> 
> current.
> 
>>Any suggestions are appreciated.
>>
>>Thanks,
>>Edwin
>>
>>
>>
>>
>>
>>
>>.
>>
>> 
>>Yahoo! Groups Links
>>
>>
>>
>> 
>>
>>
>>
>>
> 
> 
> 
> 
> 
> .
> 
>  
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 
> 
> 
> 
> 
> 
> 
> .
> 
>  
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 
> 
>