hi all,

I want to connect up the reference pins to get the ADC going on my 
MSP430F1491. Am I right in saying that i connect Vref+ and VeREF+ to 
Vcc and VREF- to ground?

this is what i have done in the past with other microcontrollers but 
just checking if thats the correct usage here.

cheers

Yuri Johnson

Hi Yuri,

> I want to connect up the reference pins to get the
ADC going on my 
> MSP430F1491. Am I right in saying that i connect Vref+ and VeREF+ to 
> Vcc and VREF- to ground?
> 
> this is what i have done in the past with other microcontrollers but 
> just checking if thats the correct usage here.

Not correct, they mean different things here.
Vref+ is to provide decoupling/bypassing on the internal reference, should you
use it.
VeREF+ is to provide an external reference, and also bypassing for it.

Whether you use internal reference, external, or Vcc/GND is decided in SW in
ADC12MCTLx regs.
There you also decide whether GND or VREF- is used etc etc.
If you use Vcc/GND as reference, you don't need extra components on Vref+
etc. pins.
AFAIK.

Have a good read of SLAU049d.pdf on ADC12 section.

B rgds
Kris

Hi Yuri, and Kris. You SHOULD decouple Vref+ even if you don't use it.

When not in use it can still couple noise onto the reference. There was 
a note on this from TI some time ago. So the rule is decouple VeRef+, 
VRef+ abd Vcc. I do believe this is shown in the latest versions of the 
Tech data sheet.. The purpose of Vref+ is to provide the internal 
reference for use by other chips.

Al

microbit wrote:

>Hi Yuri,
>
>  
>
>>I want to connect up the reference pins to get the ADC going on my 
>>MSP430F1491. Am I right in saying that i connect Vref+ and VeREF+ to 
>>Vcc and VREF- to ground?
>>
>>this is what i have done in the past with other microcontrollers but 
>>just checking if thats the correct usage here.
>>    
>>
>
>Not correct, they mean different things here.
>Vref+ is to provide decoupling/bypassing on the internal reference, should
you use it.
>VeREF+ is to provide an external reference, and also bypassing for it.
>
>Whether you use internal reference, external, or Vcc/GND is decided in SW in
>ADC12MCTLx regs.
>There you also decide whether GND or VREF- is used etc etc.
>If you use Vcc/GND as reference, you don't need extra components on
Vref+ etc. pins.
>AFAIK.
>
>Have a good read of SLAU049d.pdf on ADC12 section.
>
>B rgds
>Kris
>
>
>
>
>.
>
> 
>Yahoo! Groups Links
>
>
>
> 
>
>
>
>
>  
>

Hi Al,

> Hi Yuri, and Kris. You SHOULD decouple Vref+ even
if you don't use it. 
> When not in use it can still couple noise onto the reference. There was 
> a note on this from TI some time ago. So the rule is decouple VeRef+, 
> VRef+ abd Vcc. I do believe this is shown in the latest versions of the 
> Tech data sheet.. 

Thanks for the heads-up Al, did not know that.
As a rule I decouple it, although if it's cramped - and I use AVcc/GND as
ref. anyway -
I don't bypass. Seem to have been able to reach close to 1 LSB in the past
like that.
(at least, without 10 uF, just 100 nF, but good quality).

> The purpose of Vref+ is to provide the internal 
> reference for use by other chips.

Woh :-)
That reference sucks :-)
Your garden variety LDO provides way more temp stability and precision than that
beastie :-)
I like to use AVcc/GND, but that's me......
When it gets to DAC12, different story of course :-(

Cheers,
Kris

Just to remember, the MSP430F1491 does NOT have ADC, but the '149 has it.

Regards,
Adriano.

Onestone wrote:
> Hi Yuri, and Kris. You SHOULD decouple Vref+ even if you don't use it.

> When not in use it can still couple noise onto the reference. There was 
> a note on this from TI some time ago. So the rule is decouple VeRef+, 
> VRef+ abd Vcc. I do believe this is shown in the latest versions of the 
> Tech data sheet.. The purpose of Vref+ is to provide the internal 
> reference for use by other chips.
> 
> Al
> 
> microbit wrote:
> 
> 
>>Hi Yuri,
>>
>> 
>>
>>
>>>I want to connect up the reference pins to get the ADC going on my 
>>>MSP430F1491. Am I right in saying that i connect Vref+ and VeREF+ to

>>>Vcc and VREF- to ground?
>>>
>>>this is what i have done in the past with other microcontrollers but

>>>just checking if thats the correct usage here.
>>>   
>>>
>>
>>Not correct, they mean different things here.
>>Vref+ is to provide decoupling/bypassing on the internal reference,
should you use it.
>>VeREF+ is to provide an external reference, and also bypassing for it.
>>
>>Whether you use internal reference, external, or Vcc/GND is decided in
SW in
>>ADC12MCTLx regs.
>>There you also decide whether GND or VREF- is used etc etc.
>>If you use Vcc/GND as reference, you don't need extra components on
Vref+ etc. pins.
>>AFAIK.
>>
>>Have a good read of SLAU049d.pdf on ADC12 section.
>>
>>B rgds
>>Kris
>>
>>
>>
>>
>>.
>>
>>
>>Yahoo! Groups Links
>>
>>
>>
>>
>>
>>
>>
>>
>> 
>>
> 
> 
> 
> 
> 
> .
> 
>  
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 

I know the internal ref is crap, but whther its used or not it appears 
that it can inject noise. Whether this is apparent or not depends on any 
other tghings you may do like filtering. You can get 1 LSB stability at 
very high sample rates without averaging , but not usually if you don't 
decouple this. I learned this the very hard way, my very first design 
had no decoupling on Vref, even though it wasn't used, and at higher 
sample rates I had less stability than expected. I ended up having to 
compromise with additional filters.

Al

microbit wrote:

>Hi Al,
>
>  
>
>>Hi Yuri, and Kris. You SHOULD decouple Vref+ even if you don't use
it. 
>>When not in use it can still couple noise onto the reference. There was 
>>a note on this from TI some time ago. So the rule is decouple VeRef+, 
>>VRef+ abd Vcc. I do believe this is shown in the latest versions of the 
>>Tech data sheet.. 
>>    
>>
>
>Thanks for the heads-up Al, did not know that.
>As a rule I decouple it, although if it's cramped - and I use AVcc/GND
as ref. anyway -
>I don't bypass. Seem to have been able to reach close to 1 LSB in the
past like that.
>(at least, without 10 uF, just 100 nF, but good quality).
>
>  
>
>>The purpose of Vref+ is to provide the internal 
>>reference for use by other chips.
>>    
>>
>
>Woh :-)
>That reference sucks :-)
>Your garden variety LDO provides way more temp stability and precision than
that beastie :-)
>I like to use AVcc/GND, but that's me......
>When it gets to DAC12, different story of course :-(
>
>Cheers,
>Kris
>
>
>
>
>.
>
> 
>Yahoo! Groups Links
>
>
>
> 
>
>
>
>
>  
>

Hi,

the manual says you should use 100 nF + 10 uF on 
DVcc, AVcc, Veref+, Vref+, Vref-/Veref-.
It says clearly that the caps on Vref+ are used for 
stabilizing the internal reference generator and i think
that's trivial.

Regards,

Rolf


msp430@msp4... schrieb am 04.08.05 17:23:41:
> 
> I know the internal ref is crap, but whther its used or not it appears 
> that it can inject noise. Whether this is apparent or not depends on any 
> other tghings you may do like filtering. You can get 1 LSB stability at 
> very high sample rates without averaging , but not usually if you
don't 
> decouple this. I learned this the very hard way, my very first design 
> had no decoupling on Vref, even though it wasn't used, and at higher 
> sample rates I had less stability than expected. I ended up having to 
> compromise with additional filters.
> 
> Al
> 
> microbit wrote:
> 
> >Hi Al,
> >
> >  
> >
> >>Hi Yuri, and Kris. You SHOULD decouple Vref+ even if you don't
use it. 
> >>When not in use it can still couple noise onto the reference. There
was 
> >>a note on this from TI some time ago. So the rule is decouple
VeRef+, 
> >>VRef+ abd Vcc. I do believe this is shown in the latest versions of
the 
> >>Tech data sheet.. 
> >>    
> >>
> >
> >Thanks for the heads-up Al, did not know that.
> >As a rule I decouple it, although if it's cramped - and I use
AVcc/GND as ref. anyway -
> >I don't bypass. Seem to have been able to reach close to 1 LSB in
the past like that.
> >(at least, without 10 uF, just 100 nF, but good quality).
> >
> >  
> >
> >>The purpose of Vref+ is to provide the internal 
> >>reference for use by other chips.
> >>    
> >>
> >
> >Woh :-)
> >That reference sucks :-)
> >Your garden variety LDO provides way more temp stability and precision
than that beastie :-)
> >I like to use AVcc/GND, but that's me......
> >When it gets to DAC12, different story of course :-(
> >
> >Cheers,
> >Kris
> >
> >
> >
> >
> >.
> >
> > 
> >Yahoo! Groups Links
> >
> >
> >
> > 
> >
> >
> >
> >
> >  
> >
> 
> 
> 
> 
> .
> 
>  
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 
> 

Try it and see.

Al

rolf.freitag@rolf... wrote:

>Hi,
>
>the manual says you should use 100 nF + 10 uF on 
>DVcc, AVcc, Veref+, Vref+, Vref-/Veref-.
>It says clearly that the caps on Vref+ are used for 
>stabilizing the internal reference generator and i think
>that's trivial.
>
>Regards,
>
>Rolf
>
>
>msp430@msp4... schrieb am 04.08.05 17:23:41:
>  
>
>>I know the internal ref is crap, but whther its used or not it appears 
>>that it can inject noise. Whether this is apparent or not depends on any

>>other tghings you may do like filtering. You can get 1 LSB stability at 
>>very high sample rates without averaging , but not usually if you
don't 
>>decouple this. I learned this the very hard way, my very first design 
>>had no decoupling on Vref, even though it wasn't used, and at
higher 
>>sample rates I had less stability than expected. I ended up having to 
>>compromise with additional filters.
>>
>>Al
>>
>>microbit wrote:
>>
>>    
>>
>>>Hi Al,
>>>
>>> 
>>>
>>>      
>>>
>>>>Hi Yuri, and Kris. You SHOULD decouple Vref+ even if you
don't use it. 
>>>>When not in use it can still couple noise onto the reference.
There was 
>>>>a note on this from TI some time ago. So the rule is decouple
VeRef+, 
>>>>VRef+ abd Vcc. I do believe this is shown in the latest versions
of the 
>>>>Tech data sheet.. 
>>>>   
>>>>
>>>>        
>>>>
>>>Thanks for the heads-up Al, did not know that.
>>>As a rule I decouple it, although if it's cramped - and I use
AVcc/GND as ref. anyway -
>>>I don't bypass. Seem to have been able to reach close to 1 LSB
in the past like that.
>>>(at least, without 10 uF, just 100 nF, but good quality).
>>>
>>> 
>>>
>>>      
>>>
>>>>The purpose of Vref+ is to provide the internal 
>>>>reference for use by other chips.
>>>>   
>>>>
>>>>        
>>>>
>>>Woh :-)
>>>That reference sucks :-)
>>>Your garden variety LDO provides way more temp stability and
precision than that beastie :-)
>>>I like to use AVcc/GND, but that's me......
>>>When it gets to DAC12, different story of course :-(
>>>
>>>Cheers,
>>>Kris
>>>
>>>
>>>
>>>
>>>.
>>>
>>>
>>>Yahoo! Groups Links
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> 
>>>
>>>      
>>>
>>
>>
>>.
>>
>> 
>>Yahoo! Groups Links
>>
>>
>>
>> 
>>
>>
>>
>>    
>>
>
>
>
>
>
>.
>
> 
>Yahoo! Groups Links
>
>
>
> 
>
>
>
>
>  
>

> the manual says you should use 100 nF + 10 uF on 
> DVcc, AVcc, Veref+, Vref+, Vref-/Veref-.
> It says clearly that the caps on Vref+ are used for 
> stabilizing the internal reference generator and i think
> that's trivial.
> 
> Regards,
> 
> Rolf

Yeah, but it also clearly states that if you don't use internal Vref at
all, 100 nF + 10 uF
is not needed at all !
According to Al it is needed.

I got 1 LSB allright without problem with my own PCB layout not using 10 uF,
athough I must say that my sample rates were only hundreds of times /sec.

B rgds
Kris