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MC3S12RG128 Datasheet, PDF (518/546 Pages) Freescale Semiconductor, Inc – Microcontrollers
Appendix A Electrical Characteristics
Table A-10. ATD Operating Characteristics
Conditions are shown in Table A-4 unless otherwise noted; Supply Voltage 3.3V-10% <= VDDA <= 3.3V+10%
Num C
Rating
Symbol
Min
Typ
Max
Unit
1 D Reference Potential
Low
VRL
High VRH
VSSA
VDDA/2
VDDA/2
V
VDDA
V
2 C Differential Reference Voltage
VRH-VRL
3.0
3.3
3.6
V
3 D ATD Clock Frequency
fATDCLK
0.5
2.0
MHz
4 D ATD 10-Bit Conversion Period
Clock Cycles1 NCONV10
14
Conv, Time at 2.0MHz ATD Clock fATDCLK TCONV10
7
28
Cycles
14
µs
5 D ATD 8-Bit Conversion Period
Clock Cycles1 NCONV8
12
Conv, Time at 2.0MHz ATD Clock fATDCLK TCONV8
6
26
Cycles
13
µs
6 D Recovery Time (VDDA=3.3 Volts)
tREC
20
µs
7 P Reference Supply current
IREF
0.2502
mA
1 The minimum time assumes a final sample period of 2 ATD clocks cycles while the maximum time assumes a final sample
period of 16 ATD clocks.
2 This applies per ATD module, i.e. for 2 ATD modules this number is doubled.
A.2.3 Factors influencing accuracy
Three factors - source resistance, source capacitance and current injection - have an influence on the
accuracy of the ATD.
A.2.3.1 Source Resistance:
Due to the input pin leakage current as specified in Table A-7 in conjunction with the source resistance
there will be a voltage drop from the signal source to the ATD input. The maximum source resistance RS
specifies results in an error of less than 1/2 LSB (2.5mV) at the maximum leakage current. If device or
operating conditions are less than worst case or leakage-induced error is acceptable, larger values of source
resistance is allowable.
A.2.3.2 Source capacitance
When sampling an additional internal capacitor is switched to the input. This can cause a voltage drop due
to charge sharing with the external and the pin capacitance. For a maximum sampling error of the input
voltage ≤ 1LSB, then the external filter capacitor, Cf ≥ 1024 * (CINS- CINN).
MC3S12RG128 Data Sheet, Rev. 1.05
518
Freescale Semiconductor