Why do I need to use a unity gain amplifier to measure DAC output voltage of a PIC16F1xxx?

The DAC has a source impedance of about 300 kΩ. Load resistance may be low enough that it could draw a large current that would eventually decrease the output voltage. Adding an opamp, in unity gain amplifier configuration, copies the input voltage to its output terminal while drawing lower DAC output current. This is because the input impedance of an opamp is very high and buffers the load from the DAC output. The output of the opamp can then supply the required amount of current based on the opamp output current specifications.

© 2018 Microchip Technology, Inc.
Notice: ARM and Cortex are the registered trademarks of ARM Limited in the EU and other countries.
Information contained on this site regarding device applications and the like is provided only for your convenience and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. MICROCHIP MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED, WRITTEN OR ORAL, STATUTORY OR OTHERWISE, RELATED TO THE INFORMATION, INCLUDING BUT NOT LIMITED TO ITS CONDITION, QUALITY, PERFORMANCE, MERCHANTABILITY OR FITNESS FOR PURPOSE. Microchip disclaims all liability arising from this information and its use. Use of Microchip devices in life support and/or safety applications is entirely at the buyer's risk, and the buyer agrees to defend, indemnify and hold harmless Microchip from any and all damages, claims, suits, or expenses resulting from such use. No licenses are conveyed, implicitly or otherwise, under any Microchip intellectual property rights.