ST72321 datasheet(165/185 Pages) STMICROELECTRONICS

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ST72321

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12.12 10-BIT ADC CHARACTERISTICS

Subject to general operating conditions for VDD, fCPU, and TA unless otherwise specified.

Figure 100. RAIN max. vs fADC with CAIN=0pF

Figure 101. Recommended CAIN & RAIN values.

Figure 102. Typical A/D Converter Application

Notes:

1. Unless otherwise specified, typical data are based on TA=25°C and VDD-VSS=5V. They are given only as design guide-

lines and are not tested.

2. When VDDA and VSSA pins are not available on the pinout, the ADC refers to VDD and VSS.

3. Any added external serial resistor will downgrade the ADC accuracy (especially for resistance greater than 10k

Ω). Data

based on characterization results, not tested in production.

4. CPARASITIC represents the capacitance of the PCB (dependent on soldering and PCB layout quality) plus the pad ca-

pacitance (3pF). A high CPARASITIC value will downgrade conversion accuracy. To remedy this, fADC should be reduced.

5. This graph shows that depending on the input signal variation (fAIN), CAIN can be increased for stabilization time and

decreased to allow the use of a larger serial resistor (RAIN).

Symbol

Parameter

Conditions

Min

Typ 1)

Max

Unit

fADC

ADC clock frequency

0.4

MHz

VAREF

Analog reference voltage 2)

0.7*VDD≤VAREF≤VDD

3.8

5.5

VAIN

Conversion voltage range 3)

VSSA

VAREF

Input leakage current

for analog input

-40°C

≤T

A≤85°C range

±250

Other TA ranges

±1

µA

RAIN

External input impedance

see

Figure

100 and

Figure

1013)4)5)

Ω

CAIN

External capacitor on analog input

fAIN

Variation freq. of analog input signal

CADC

Internal sample and hold capacitor

tSTAB

Stabilization time after ADC enable

fCPU=8MHz, SPEED=0

fADC=2MHz

0 5)

µs

tADC

Conversion time (Sample+Hold)

7.5

- No of sample capacitor loading cycles

- No. of Hold conversion cycles

1/fADC

010

CPARASITIC (pF)

2 MHz

1 MHz

0.1

100

1000

0.01

0.1

fAIN(KHz)

Cain 10 nF

Cain 22 nF

Cain 47 nF

AINx

ST72XXX

VDD

±1

µA

0.6V

CADC

12pF

VAIN

RAIN

10-Bit A/D

Conversion

Ω(max)

CAIN

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