SD16_A of MSP430F2013

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kuber
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Location: India, Karnataka, Hubli
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SD16_A of MSP430F2013

Post by kuber » Thu Nov 27, 2008 12:40 am

Hi to All,

Can you help me. We are working with msp430f2013 series on that am using SD16, but am facing one problem with that waht ever dig value am giving its not equal to or nearly equal to m input analog voltage. What may be the problem can help us?
Thanks and Best Regards
Kuber

engrforever
Posts: 10
Joined: Mon Feb 16, 2009 12:39 pm

Post by engrforever » Tue Mar 10, 2009 3:58 pm

Kuber,

I am having similar problems on an MSP430FE427 board, how did you resolve your issue?
Sincerely,
Engrforever

gm
Posts: 203
Joined: Fri May 04, 2007 3:08 pm

Post by gm » Wed Mar 11, 2009 6:36 am

Kuber,

IIRC, the specs of the SD16 on the '2013 indicate that if you are within 20% of the rails, the linearity suffers. In other words, you can use only the middle 60% of the voltage range between -Vref and +Vref.

Also, are you using the recommended capacitors on the reference supplies?

HTH,

gm

engrforever
Posts: 10
Joined: Mon Feb 16, 2009 12:39 pm

Post by engrforever » Wed Mar 11, 2009 8:50 am

gm wrote:Kuber,

IIRC, the specs of the SD16 on the '2013 indicate that if you are within 20% of the rails, the linearity suffers. In other words, you can use only the middle 60% of the voltage range between -Vref and +Vref.
gm,

Wha tis IIRC? I was looking at the MSP430FE427 documentation and could not find anything similar.

Thank you for your time!
Sincerely,
Engrforever

gm
Posts: 203
Joined: Fri May 04, 2007 3:08 pm

Post by gm » Wed Mar 11, 2009 9:49 am

I looked at the specs on the '427 and there is a note regarding the range at the bottom of page 28 of the current data sheet:
2. The analog input range depends on the reference voltage applied to VREF. If VREF is sourced externally, the full-scale range
is defined by VFSR+ = +(VREF/2)/GAIN and VFSR− = −(VREF/2)/GAIN. The analog input range should not exceed 80% of
VFSR+ or VFSR−.
I mentioned this to a TI Rep at one of the MSP430 meetings and he said it was due to the protection diodes on the inputs.

gm

P.S. - IIRC means "If I recall correctly"

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