4.1 Sinking or Sourcing Current from the DAC

Symptoms:

• DAC output voltage is not the expected value under load

Troubleshooting:

• Remove the load and measure
• Verify the output is enabled
• Measure the voltage reference (if external)

In some cases, the load connected to the DAC may use more current than the DAC can sink or source, causing the voltage output to shift. This can be tested by removing the load from the DAC and measuring the output. If the output is as expected, then the DAC cannot drive the load directly.

The DAC can be buffered by an OPAMP to increase the current drive capacity. Some microcontrollers contain dedicated op amp peripherals that can be used for this purpose⁽¹⁾.

Another possibility is that the DAC is enabled, but the output has not been. Some microcontrollers have a register that controls which pin the DAC output goes to. If set incorrectly, the output will not appear where expected or not at all.

The last possibility to consider is the voltage reference. The DAC can use a variety of voltage references, including externally provided references. The DAC reference setting has to be verified to ensure it is correctly set. In addition, the external reference can be measured to verify it is operating as expected.