AN1812 datasheet(22/34 Pages) STMICROELECTRONICS

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11 Result

AN1812

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Figure 17 shows the relationship between measured voltages Vmeasured (average of the 16

readings measured by the converter) and input voltage Vin (As measured by the multimeter) for

negative voltages.

Figure 17. Measured vs input for negative voltages

Figure 18. Error vs input for negative input voltages

Note:

In Figure 18, we see that for the negative input voltages varying from 0 to -1V, the maximum

error is around -2.89mV for -1V input. The error of 0.5 mV occurs for the input value of -269 mV

and it increases gradually afterwards. The maximum difference between maximum value and

the minimum in loop is around 600 uV. So the accuracy of the average value measured is

around 3 mV, and without averaging the accuracy is around 3.6 mV.

11.3

Effect of the capacitor value

As discussed in error analysis (Section 7), reducing the R*C time constant by reducing the

value of R or C, will reduce the accuracy. We have also taken the reading for the capacitor value

of 10 uF. This shows that the accuracy of the ADC is reduced. An example is given in Figure 19

of readings with a 10 uF capacitor.

AN1812 Datasheet(PDF) 22 Page - STMicroelectronics