ST7262 datasheet(122/132 Pages) STMICROELECTRONICS

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ST7262

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ADC CHARACTERISTICS (Cont’d)

ADC Accuracy with fCPU=8 MHz, fADC=4 MHz RAIN< 10kΩ

Figure 90. ADC Accuracy Characteristics

Notes:

1) Not tested in production, guaranteed by characterization.

2) ADC Accuracy vs. Negative Injection Current:

Injecting negative current on any of the analog input pins significantly reduces the accuracy of the conversion being per-

formed on another analog input.

For IINJ-=0.8mA, the typical leakage induced inside the die is 1.6µA and the effect on the ADC accuracy is a loss of 4 LSB

for each 10K

Ω increase of the external analog source impedance. It is recommended to add a Schottky diode (pin to

ground) to analog pins which may potentially inject negative current. Any positive injection current within the limits spec-

ified for IINJ(PIN) and ΣIINJ(PIN) in Section 12.8 does not affect the ADC accuracy.

Symbol

Parameter

Conditions

Typ

Max

Unit

|ET|

Total unadjusted error

VDD= 4V-5.5V

3 1)

LSB

|EO|

Offset error

1 1)

2 1)

|EG|

Gain Error

0.7 1)

2 1)

|ED|

Differential linearity error

1.3 1)

2 1)

|EL|

Integral linearity error

2.9 1)

5 1)

1LSBIDEAL

1LSB

IDEA L

DDA

SSA

–

1024

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

Vin (LSBIDEAL)

(1) Example of an actual transfer curve

(2) The ideal transfer curve

(3) End point correlation line

ET=Total Unadjusted Error: maximum deviation

between the actual and the ideal transfer curves.

EO=Offset Error: deviation between the first actual

transition and the first ideal one.

EG=Gain Error: deviation between the last ideal

transition and the last actual one.

ED=Differential Linearity Error: maximum deviation

between actual steps and the ideal one.

EL=Integral Linearity Error: maximum deviation

between any actual transition and the end point

correlation line.

Digital Result ADCDR

1023

1022

1021

345

1021 1022 1023 1024

(1)

(2)

(3)

VDDA

VSSA

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