ADC reference

[togrady]

Posted on January 03, 2009 at 14:39

ADC reference

[togrady]

Posted on May 17, 2011 at 12:19

I've just read that on 64 pin version of the STMF103xB the ADC ref pins are not brought out and instead are connected to VDDA and VSSA. VDDA is only going to be as accurate as the supply voltage regulator. Do I need to find a precision voltage regulaor (if such a thing exists) for VDDA? Does anyone have any other ideas on this?

I waw thinking of maybe connecting a precision reference to one of the analog inputs and use the reading from this to calibrate (in software) my real analog inputs. I only need a reading every few minutes so sample frequency isn't an issue. My sensor output range is 0 - 2.5V Regards Trevor

[16-32micros]

Posted on May 17, 2011 at 12:19

Hi togrady,

Good idea, you can use for example the TS821 1.225 Shunt voltage reference ( B Grade +/- 0.5%) here attached its datasheet + a Resitor. Or even better (without extra hardware) you can use the internal STM32 Voltage reference connected to ADC Channel 17. Below a screenshot from STM32 Datasheet. All depends on your sensor output senvitivity. ;-), Regards STOne-32 [ This message was edited by: STOne-32 on 08-12-2007 20:27 ]

[togrady]

Posted on May 17, 2011 at 12:19

Thank you STOne-32. I think I can use the internal reference.

[obtronix]

Posted on May 17, 2011 at 12:19

remember the int ref is only accurate to about 10% (about 6.5 bits or so)

you can buy precision regulators (ie., references that can source 50mA)

[obtronix]

Posted on May 17, 2011 at 12:19

here is a .05% 20mA

http://www.national.com/pf/LM/LM4132.html 30mA http://datasheets.maxim-ic.com/en/ds/MAX6173-MAX6177.pdf how much current do you need? what precision?

[var]

Posted on May 17, 2011 at 12:19

Hi, obtronix

Can you reference at least one of such regulators? Thank you Varuzhan

[togrady]

Posted on May 17, 2011 at 12:19

Thanks obtronix.

I only need whatever current the STM VDDA pin takes plus about 200uA for other analog stuff. The LM4132 looks like an interesting part. The quiescent current is a little high (60uA)-- ideally I would like something under 30uA. I wonder how much current VDDA on the STM32 requires? Maybe I could put the VDDA regulator in shut down mode when the processor is in standby mode. If I could do this the quiescent current would not matter. Regards Trevor

[cosmapa]

Posted on May 17, 2011 at 12:19

I intend to use a LD1117S33CTR voltage regulator to provide the 3.3V MCU. This regulator is rated at 1%. Does this mean that I can also expect 1% precision off the ADC?

[obtronix]

Posted on May 17, 2011 at 12:19

Quote:

On 11-12-2007 at 11:24, Anonymous wrote: I intend to use a LD1117S33CTR voltage regulator to provide the 3.3V MCU. This regulator is rated at 1%. Does this mean that I can also expect 1% precision off the ADC? that is actualy a 2% part (over temp, it's 1% at 25 deg C), and yes, the a/d is only as accurate as it reference.