AN2615 datasheet(29/37 Pages) STMICROELECTRONICS

Part #	AN2615

Description	In general the ADC embedded in the ST7 microcontroller

PDF	37 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

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29 / 37 page

AN2615

Input stage conditions

29/37

Appendix A

Input stage conditions

The ADC described here can be used for measuring both voltage and current with slight

changes in set-up in each case.

A.1

Case 1: Voltage measurement

There are two ways in which the input voltage appears at the ADC input. The first way is that

input comes directly from a voltage source as shown in Figure 20.

Figure 20.

Voltage measurement

In Figure 20 above, there are no problems. However, if the input comes from a potential

divider circuit as shown in Figure 21, the effective input voltage Vin is the result of the drop

across R2 due to the current I and current Iin.

Figure 21.

Potential divider

In this case an input buffer has to be used to overcome the problem (see Figure 22: Use of

input buffer for voltage measurement on page 30).

O/p

VIN

Gnd

VIN

Iin

AN2615 Datasheet(PDF) 29 Page - STMicroelectronics