AN3322 datasheet(12/38 Pages) STMICROELECTRONICS

12 / 38 page

Watt-hour meter using the STM32

AN3322

12/38

DocID18304 Rev 1

Example 3

With the setting used in this application ADCCLK = 9 MHz and a sampling time of 1.5

cycles:

Tconv_9MHz = 1.5 + 12.5 = 14 cycles = 1.56 µs

TSampling_time = (1.5 cycles / 14 cycles) x 1.56 µs = 167 ns

Figure 4. Internal and external analog input pin capacitors and resistors

Equation 6

R129 = 820  and R137 = 820  (resistors between an output of op amp and an ADC input)

RAIN = R129 = R137 = 820 

ROpAmp = 80 

= RC = (RADC + RAIN) + ROpAmp) C = 1900  x 12 pF = 22.8 ns

Error % = 100 x exp. [-1 x (TSampling_time/ )]

From Table 3 it is recommended to use every second value sampled on the same channel.

This approach renders an error caused by this phenomenon negligible.

Table 2. STM32 ADC input characteristics specifications

Symbol

Parameter

Conditions Min.

Typ.

Max.

Unit

RADC

Sampling switch resistance



CADC

Internal sample and hold capacitor

Table 3. Crosstalk between subsequent multiplexed channels

Number of the same channel readings [-]

Tconv [cycle / µs] TSampling_time [ns] Error [%]

1.5 / 1.55

167

0.07

3.0 / 3.10

334

0.00

4.5 / 4.65

501

0.00

6.0 / 6.20

668

0.00

AN3322 Datasheet(PDF) 12 Page - STMicroelectronics

AN3322 Datasheet(HTML) 12 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38

Datasheet Download

Link URL