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Current consumption into ADVREF pin of SAM3N00B microcontroller?

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T

treez

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We are using an external reference for our micro (for the ADC and DAC)

Table 35-33 (page 719) of the SAM3N00B datasheet appears to say that the current drawn from the ADVREF pin by the micro's ADC module is 250uA.
Is this correct?
If it really is that much then that means the micro's external voltage reference circuitry (based around a TLV431) will not be able to keep the reference constant at 3.064V (due to the volt drop across the 220R resistor in the external voltage reference circuit)
The following is the external reference circuitry connected to the ADVREF pin of the SAM3N00B microcontroller.......

External Voltage reference circuit feeding the ADVREF pin (also attached in pdf)
http://i41.tinypic.com/2qxrmug.jpg



Table 35-35 on page 720 says that a further 300uA is drawn into the ADVREF pin by the micro's DAC module.
This makes things even worse.

Does this much current really get drawn into the ADVREF pin by the microcontroller?

SAM3N00B microcontroller datasheet:
http://www.atmel.com/Images/doc11011.pdf
 

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The circuit will work according to TLV431 minimum cathode current (about 100 µA) with Vdd of 3.3 V. Depending on minimum Vdd voltage, the TLV431 bias current might need to be increased (reduce the value of the 220R resistor).
 

Tha supply voltage is 3v3.
So you think those currents really do flow through the 220R resistor...i.e. 550uA when the ADC and DAC are working.
 

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