DAC output limitations of microcontroller's on-chip DAC

[Flyback]

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:
https://www.electro-tech-online.com/custompdfs/2013/05/doc11011-3.pdf

 

[misterT]

You might run into problems there. What kind of signal are you generating and what do you have connected after the RC filter? You might need an active filter.. or an op amp buffer somewhere.

 

[Flyback]

after the RC filter its the non-inverting input of an opamp.
The signal from the DAC is literally just a fixed DC voltage .

 

[misterT]

after the RC filter its the non-inverting input of an opamp.
The signal from the DAC is literally just a fixed DC voltage .

I think your system will work just fine.

Actually the specs of the DAC are little confusing. I think the 5 kohm load means series output resistance of the DAC output. And the 50pF means output capacitance of the DAC pin. They are not the limits what you can connect to it. But, I might be wrong also. I have not worked much with DACs.

 

[blueroomelectronics]

Always buffer the outputs on a µC DAC. Many single rail OpAmps will do nicely.

 

[dougy83]

Actually the specs of the DAC are little confusing. I think the 5 kohm load means series output resistance of the DAC output. And the 50pF means output capacitance of the DAC pin. They are not the limits what you can connect to it. But, I might be wrong also. I have not worked much with DACs.

Table 35-38 states that the output load resistance > 5k and the output load capacitance < 50pF. These are not pin parasitics, but load values.

I do agree with you that there shouldn't be any problem driving a non-inverting opamp input.

 

[Flyback]

I do agree with you that there shouldn't be any problem driving a non-inverting opamp input.

..but its driving it via a 1K/100p RC filter, and 100p > 50p, so is it still OK?

 

[dougy83]

I would think so. If you are still worried, just replace the 1K resistor with a 5K