ST7262 datasheet(120/139 Pages) STMICROELECTRONICS

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12.12 10-BIT ADC CHARACTERISTICS

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

Figure 81. RAIN max. vs fADC with CAIN=0pF

Figure 82. Recommended CAIN/RAIN values

Figure 83. Typical Application with ADC

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 and to allow

the use of a larger serial resistor (RAIN). It is valid for all fADC frequencies ≤ 4MHz.

6. Please refer to Important Notes on conversion speed, Section 15.2 and also to Figure 92. on page 137 for details on

silicon revision identification.

Symbol

Parameter

Conditions

Min

Typ 1)

Max

Unit

fADC

ADC clock frequency

0.4

MHz

VAIN

Conversion voltage range 2)

VSSA

VDDA

RAIN

External input impedance

see

Figure 81

and

Figure

823)4)5)

Ω

CAIN

External capacitor on analog input

fAIN

Variation frequency of analog input signal

CADC

Internal sample and hold capacitor

tCONV

Conversion time

Flash silicon rev. G devices

fADC=4MHz

µs

1/fADC

Conversion time

Flash silicon rev. X and ROM rev. Z devices

µs

112

1/fADC

010

CPARASITIC (pF)

4 MHz

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

6pF

VAIN

RAIN

10-Bit A/D

Conversion

Ω(max)

CAIN

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