DAC 芯片~ 16位超级好用,不容错过

DAC8501 TO 68HC11 INTERFACE

Figure 8 shows a serial interface between the DAC8501 andthe 68HC11 microcontroller. SCK of the 68HC11 drives theSCLK of the DAC8501, whereas the MOSI output drives theserial data line of the DAC. The signal is derived froma port line (PC7), similar to what was done for the 8051.

FIGURE 8. DAC8501 to 68HC11 Interface.

The 68HC11 should be configured so that its CPOL bit is a0 and its CPHA bit is a 1, this configuration causes dataappearing on the MOSI output to be valid on the falling edgeof SCK. When data is being transmitted to the DAC, theSYNC line is taken LOW (PC7). Serial data from the 68HC11is transmitted in 8-bit bytes with only eight falling clock edgesoccurring in the transmit cycle, data is transmitted MSB first.In order to load data to the DAC8501, PC7 is left LOW afterthe first eight bits are transferred, then a second and thirdserial write operation is performed to the DAC and PC7 istaken HIGH at the end of this procedure.

FIGURE 9. REF02 as a Power Supply to the DAC8501.are at some value other than 5V. The REF02 will output asteady supply voltage for the DAC8501; if the REF02 is used,the typical current it needs to supply to the DAC8501 is285µA. This is with no load on the output of the DAC. Whenthe DAC output is loaded, the REF02 also needs to supplythe current to the load. The total current required (with a 5k load on the DAC output) is:

285µA + (5V/5k ) = 1.29mA

(2)

The load regulation of the REF02 is typically 0.005%/mA,which results in an error of 322µV for the 1.29mA currentdrawn from it. This corresponds to a 4.2LSB error.

APPLICATIONS

USING REF02 AS A POWER SUPPLY FOR THE DAC8501

Due to the extremely low supply current required by theDAC8501, an alternative option is to use a REF02 +5Vprecision voltage reference to supply the required voltage tothe part, as shown in Figure 9. This is especially useful if thepower supply is quite noisy or if the system supply voltages

BIPOLAR OPERATION USING THE DAC8501

The DAC8501 has been designed for single-supply operationbut a bipolar output range is also possible using the circuit inFigure 10. The circuit shown will give an output voltage rangeof ±VREF. Rail-to-rail operation at the amplifier output isachievable using an OPA703 as the output amplifier.

FIGURE 10. Bipolar Operation with the DAC8501.

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DAC8501

SBAS212A