5 years, 5 months ago.

What is the maximum current from analog out (pin 18) for LPC1768?

Hi, i just want to ask what is the maximum current that can output at pin 18

2 Answers

5 years, 5 months ago.

For that sort of thing you normally need to look at the CPU manufacturers datasheet.

Unfortunately the datasheet for the LPC1768 here doesn't explicitly state a maximum current for the DAC. It does indicate that the normal outputs are able to drive at least +/- 4mA with minimal impact on the output voltage.

The only analog out specific information is on page 69 which indicates that that load on the DAC output should be at least 1kOhm which would give currents in the couple of mA region.

So if you try to pull anything over 3-4mA on that pin you'll probably start to see distortion in the output.

3 years ago.

I realize this post is 2 years old, but for anyone else with this question:

The 1K load does indeed dictate maximum current draw for the DAC. I have an audio circuit attached to the DAC on my MBED and I initially did a voltage divider of 270-ohms over 150-ohms to bring the voltage input to the audio amp closer to the typical 1V line-out voltage. This was no problem when initially creating square-wave sound as a DigitalOut pin, however, when I started to use the DAC I noticed it was way quieter. Sure enough, the voltage at the DAC pin was only reaching 1.4V peak due to the lower impedance on the output (420-ohms). I'll be adjusting my voltage divider to come as close to the 1K total so that I can get the maximum noise immunity, while not dragging the voltage down.