Teensy 3.2 DAC output voltage issues

[bnagelmakers]

Hi all,

I am working on a project which uses the Teensy 3.2 to simulate the output voltage of a similar device. I have the teensy connected in the following configuration:


The A14 pin in the DAC output for the Teensy 3.2 and the 5V and AGND are the Vin and AGND of the Teensy respectively. I am powering the whole system over the microUSB. When the system is powered, I observe 5V between the 5V and GND pins as is expected. Now onto the issue:

Using the following code:

uint16_t minimum = 0;
uint16_t maximum = 4095;

void setup() {
  analogWriteResolution(12);
}

void loop() {
  analogWrite(A14, minimum);
  delay(2000);
  analogWrite(A14, maximum);
  delay(2000);
}

I would expect the voltage at the A14 pin to fluctuate between 3.3V and 0V when measured against GND every 4 second period. However, I am actually reading it fluctuate between 3.3V and 1.5V. Any idea what is going on? Is there a maximum current that the Teensy 3.2 can sink on the A14 pin or is somethings else at work here?

 

[manitou]

Is there a maximum current that the Teensy 3.2 can sink on the A14 pin or is somethings else at work here?

you can check the data sheet, but I think the DAC can only source about 1 ma.

 

[bnagelmakers]

I did some measurements. It looks like it is sinking 10mA when it is pulling down to 3.3V and sinking 20mA when it is pulling down to 1.5V. My guess is that the Teensy DAC can only sink 20mA.

 

[astronomerdave]

According to the datasheet, https://www.pjrc.com/teensy/K20P64M72SF1.pdf, max output load current of the DAC is indeed 1 mA (page 46).