AN1812 datasheet(17/34 Pages) STMICROELECTRONICS

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AN1812

11 Result

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Result

The result is given for a capacitor value of 100 uF. So the conversion time is long. We can

reduce the conversion time by choosing a capacitor with a lower value but accuracy will also be

reduced. Other parameters are as follows:

R = 10 K, V1 = 1.5V, V2 = 2V and V3 = 3V

So:

R * C = (10 K) * (100 uF) = 1s

The input range is taken as +1 V to -1 V, where mod (Vref) (= 1V) is less than V1.

The conversion time is in the range 1 to 3s. The settling time (As shown in Figure 3) is kept

fixed at 1s. The ADC is calibrated by reading two known input voltages and then Koffset and

Kgain are calculated. The input voltage Vin is taken from a voltage source.

11.1

Positive input

In Figure 13, an example of the readings measured by the converter, which is sent to Hyper

Terminal, is shown. In this Tavg is the average of 16 conversions, and Vavg is the calculated

value in terms of voltage. The difference of the maximum and minimum value among the 16

values is also shown.

Figure 13. Results for positive input

In Table 1, the readings are shown for positive input voltages ranging from 0 to 1V. Here Vin is

the voltage measured by the multimeter. Vmeasured (equal to Vavg) is the average voltage

measured by the converter in a loop of 16. The last column shows the difference in the

maximum and minimum readings of the values measured by the converter in the loop. This

shows the variations recorded in the readings.

AN1812 Datasheet(PDF) 17 Page - STMicroelectronics