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DAC output of microcontroller?

eem2am

Aug 3, 2009
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Hello,

We are using the SAM3N00B microcontroller's DAC output to provide a voltage.

The DAC's output voltage goes to an RC filter which is 1K and 100p.
Page 720 of the SAM3N00B datasheet says that the max load capacitance for the DAC can be no more than 50pF.
Since our 100p is not directly connected to the DAC pin, but is after the 1K resistor, will we thus be allright using the 100p capacitor?

Also, page 720 of the SAM3N00B datasheet says that the minimum resistor load for the DAC output is 5K....does this mean that any resistor that shunts to ground from the DAC pin must be greater than 5K?

SAM3N00B DATASHEET:
http://www.atmel.com/Images/doc11011.pdf
 

BobK

Jan 5, 2010
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It means your 1K and 100p is not going to make it.

Use and opamp voltage follower as a buffer.

Bob
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
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From those specifications it's impossible to say. You're not technically violating either of the specifications, because the 100 pF capacitor is not connected _directly_ across the output and the 1k load resistor has no DC path to anything. But the combination of them does equate to some form of capacitive loading on the DAC. Personally my gut feeling is that you'd be alright but it's impossible to say for sure.

If you're designing a circuit for production use, i.e. you will be buying the device in quantity, the manufacturer would probably let you talk to an applications person, who could answer your question or find someone who could. You could always just send them an email and see what happens. Provide the full schematic including the reference voltage circuit and the circuit that follows the R-C filter.
 

eem2am

Aug 3, 2009
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Aug 3, 2009
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thanks, the cct that follows the RC is just a noninverting input of an opamp
 

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