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CCS/DAC8501: DAC8501 has wrong outputs

Part Number: DAC8501

Tool/software: Code Composer Studio

The application environment is shown as the figure. Two decoupling capacitors, i.e., 0.1uF and 1uF ceramic chip capacitors are connected to Pin 1. VDD=3.3V(3.29V by the multimeter), VREF=2.5V(2.49V by the multimeter). When several numbers of VCO are transmitted to the DAC8501, the results are given as follows.

1 VCO=0, VOUT=0(No data are transmitted to the DAC8501)

2 VCO= 0x2710; VOUT=3.28V(By the multimeter).

3 VCO= 0x851E; VOUT=3.28V(By the multimeter).

4 VCO= 0x1046a; VOUT=0V(By the multimeter).

So, are there any problems with the DAC8501 device?

  • Hi Tian Dong,

    It looks like in your schematic you do not have VFB connected to anything.  If you look at the architecture of the DAC8501 as described in the datasheet (Figure 5), you can see that the output of device is an output buffer without feedback.  This is so you can connected addition gain and offset stages easily.  At the very minimum you must connect VFB to VOUT to ensure that the output buffer has feedback.  Without feedback the buffer usually drifts to the high or low supplies, as you have seen.

    Please let me know if you have any more questions.