ST72324
12.12 10-BIT ADC CHARACTERISTICS
Subject to general operating conditions for VDD, fCPU, and TA unless otherwise specified.
Symbol
Parameter
Conditions
Min
Typ 1)
Max
fADC
VAREF
VAIN
IL
RAIN
CAIN
ADC clock frequency
Analog reference voltage 2)
Conversion voltage range 3)
Input leakage current
for analog input
External input impedance
External capacitor on analog input
fAIN Variation freq. of analog input signal
0.7*VDD≤VAREF≤VDD
-40°C≤TA≤85°C range
Other TA ranges
0.4
3.8
VSSA
2
5.5
VAREF
±250
±1
see
Figure 90
and
Figure
913)4)5)
CADC Internal sample and hold capacitor
12
tSTAB Stabilization time after ADC enable
0 5)
Conversion time (Sample+Hold)
fCPU=8MHz, SPEED=0
7.5
tADC - No of sample capacitor loading cycles fADC=2MHz
4
- No. of Hold conversion cycles
11
Unit
MHz
V
nA
µA
kΩ
pF
Hz
pF
µs
1/fADC
Figure 90. RAIN max. vs fADC with CAIN=0pF4)
45
40
35
2 MHz
30
1 MHz
25
20
15
10
5
0
0
10
30
70
CPARASITIC (pF)
Figure 92. Typical A/D Converter Application
Figure
91.
Recommended
CAIN
&
RAIN
5)
values.
1000
Cain 10 nF
100
Cain 22 nF
Cain 47 nF
10
1
0.1
0.01
0.1
1
10
fAIN(KHz)
VAIN
RAIN
AINx
CAIN
VDD
VT
0.6V
VT
0.6V
ST72XXX
2kΩ(max)
10-Bit A/D
Conversion
IL
±1µA
CADC
12pF
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 10kΩ). 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).
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