AN2353 datasheet(13/18 Pages) STMICROELECTRONICS

13 / 18 page

AN2353

Analog Digital Converter (ADC)

13/18

Analog Digital Converter (ADC)

Analog input signal error can be created by poor matching of the source internal resistance

with the ADC input parameters, which can be caused by the following occurences:

●

Voltage drop in the voltage source resistance due to input leakage current

●

Poor charging of the ADC internal capacitance (Cin)

Analog input error can also be caused by noise from the analog input signal.

This section describes each of these causes.

Figure 6.

Source internal resistance errors

6.1

Voltage drop in the source resistance

The error generated by the voltage source internal resistance is:

I(OZ1) = specified leakage current.

Refer to the latest product datasheet for the value of I(OZ1).

Note: Input leakage current is caused by parasitic current into the on-chip protection of the

input pin; this protection is necessary to protect the device against ESD (Electrical Static

Discharge) and against overload.

6.2

Poor charging of the ADC internal resistance

During the sample time, the input capacitance (CIO and CIN) must be charged/discharged by

the external source. The internal resistance of the source must allow the capacitance to

reach its final value before the end of sample time.

If this does not happen, that is, if the source resistance is mismatched to the sample time, a

voltage loss occurs at the sample and hold stage. This voltage loss causes an accuracy loss

P5.x

VIN

CIO

RSOURCE

Sample

CIN

AGND

IOZ1 (Input leakage current Port5): maximum ± 200nA (test condition: 0.45V < VIN <VDD)

CIO (Pin capacitance Port5): maximum 10pF (test condition: f = 1 MHz, TA = 25°C, guaranteed by design characterization)

CIN (ADC internal capacitance): maximum 5pF (guaranteed by design characterization)

R1 (Series input resistance): maximum 1.5k

Ω (guaranteed by design characterization)

IOZ1

Leakage

Current

error LSB

()

SOURCE

0Z1

()

AREF

AGND

–

----------------------------------------------

1024

AN2353 数据表(PDF) 13 Page - STMicroelectronics

AN2353 数据表(HTML) 13 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

数据表下载