DAC Main and Alternative Outputs

by <a href="http://community.silabs.com/t5/Welcome-and-Announcements/Community-Ranking-System-and-Recognition-Program/m-p/140490#U140490"><font color="#000000"><font size="2">Hero Employee</font></font> </a> marao on ‎03-31-2017 10:26 AM

Question

What is the difference between DAC main and alternative outputs?

Answer

Some of the EFM32 parts have one "main" output and one "alternative" output in the DAC. The main difference between these is the current drive strength of the output pins. When switching to the alternative DAC output, one often sees a reduction in drive strength. 

 

The primary reason for this is because of higher resistance between the output pin and the pad. This is roughly of the order of 1-3 kohms. The main output pin, on the other hand, has a resistance of about 10 ohms, which naturally results in the higher drive strength. 

 

Hence, if you are measuring, 2.5 V on DAC main and alternate output pins, the following behavior is expected:

 

1. The main output shows 2.5 V in no-load and under load conditions.

2. The alternative output will show 2.5 V without load. But under load conditions, it is essentially a voltage divider circuit, and a drop will be seen in the output voltage. For instance, with a 10 kohm load, a drop of about 0.2 V will be seen, and the output will be around 2.3 V on the alternative pin.