I want to supply a 0-5V signal to this process controller using the DAC8555. The DAC8555 datasheet states:

Each output buffer amplifier is capable of [...] driving a load of 2kΩ in parallel with 1000pF to GND. The source and sink capabilities of the output amplifier can be seen in the Typical Characteristics.

There's a graph showing the source current capability:

DAC8555 source current capability graph, figure 7 in DAC555 datasheet

Q1. Is the 2kΩ a minimum and the 1000pF a maximum? So it can drive >2kΩ and a capacitance of <1000pF?

The controller manual (p9) states about the 0-5V input:

NOTE: This is a current sinking device. The receiving circuit is essentially a 250 ohm resistor to ground.

Q2. Can the DAC supply this input or will it draw too much current? If so, is there a way to connect it while still getting the full 0-5V range from the DAC?

Many thanks for your help

  • 1
    \$\begingroup\$ Driving 250 ohms is beyond the given DAC output capability of 2000 ohms (min). Consider using an emitter-follower NPN circuit to boost the output current. If the Vbe drop is a problem, use an op-amp to regulate the base drive. \$\endgroup\$ – MarkU May 31 '18 at 0:00

For Q1, yes the 2 kohms is a minimum output resistance. Otherwise the DAC won't be able to source enough current and the voltage droops when you start requesting too much current for your load. The output capacitance is more about the response time for your output. If your output capacitance is too high, the RC time constant gets too large and the DAC doesn't perform as quickly as specced.

For Q2, as MarkU said I doubt the DAC can supply that much current so I'd hook it up to a Op-Amp unity buffer or some amplifier configuration.


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