286CHAPTER 15 D/A CONVERTERPD78054, 78054YANOnRR1 C• The input impedance of the buffer amplifier is R1 .• If R1 is not connected, the output becomesundefined when RESET is low.μ15.5 Cautions Related to D/A Converter(1) Output impedance of D/A converterBecause the output impedance of the D/A converter is high, use of current flowing from the ANOn pins (n =0,1) is prohibited. If the input impedance of the load for the converter is low, insert a buffer amplifier betweenthe load and the ANOn pins. In addition, wiring from the ANOn pins to the buffer amplifier or the load shouldbe as short as possible (because of high output impedance). If the wiring may be long, design the groundpattern so as to be close to those lines or use some other expedient to achieve shorter wiring.Figure 15-3. Use Example of Buffer Amplifier(a) Inverting amplifier(b) Voltage-follower(2) Output voltage of D/A converterBecause the output voltage of the converter changes in steps, use the D/A converter output signals in generalby connecting a low-pass filter.(3) AV REF1 pinWhen only either one of the D/A converter channels is used with AV REF1 < V DD , the other pins that are not usedas analog outputs must be set as follows:• Set PM13x bit of the port mode register 13 (PM13) to 1 (input mode) and connect the pin to V SS .• Set PM13x bit of the port mode register 13 (PM13) to 0 (output mode) and the output latch to 0, to outputlow level from the pin.μPD78054, 78054YANOnR 1CR 2• The input impedance of the buffer amplifier is R1.
