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MC9S12HZ128VAL Datasheet, PDF (632/692 Pages) Freescale Semiconductor, Inc – MC9S12HZ256 Data Sheet, Rev. 2.05 | |||
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Appendix A Electrical Characteristics
A.2 ATD
This section describes the characteristics of the analog to digital converter.
A.2.1 ATD Operating Characteristics
The Table A-8 shows conditions under which the ATD operates.
The following constraints exist to obtain full-scale, full range results:
VSSA ⤠VRL ⤠VIN ⤠VRH ⤠VDDA. This constraint exists since the sample buffer ampliï¬er can not drive
beyond the power supply levels that it ties to. If the input level goes outside of this range it will effectively
be clipped.
Table A-8. ATD Operating Characteristics
Conditions are shown in Table A-4 unless otherwise noted
Num C
Rating
Symbol
Min
Typ
Max
Unit
1 D Reference Potential
2 C Differential Reference Voltage1
Low
High
VRL
VRH
VRHâVRL
VSSA
VDDA/2
4.50
5.00
VDDA/2
V
VDDA
V
5.25
V
3 D ATD Clock Frequency
fATDCLK
0.5
2.0
MHz
4 D ATD 10-Bit Conversion Period
Clock Cycles2 NCONV10
14
Conv, Time at 2.0MHz ATD Clock fATDCLK TCONV10
7
28
Cycles
14
µs
5 D ATD 8-Bit Conversion Period
Clock Cycles2 NCONV8
12
Conv, Time at 2.0MHz ATD Clock fATDCLK TCONV8
6
26
Cycles
13
µs
6 D Stop Recovery Time (VDDA=5.0 Volts)
tSR
20
µs
7 P Reference Supply current
IREF
0.375
mA
1 Full accuracy is not guaranteed when differential voltage is less than 4.50V
2 The minimum time assumes a ï¬nal sample period of 2 ATD clocks cycles while the maximum time assumes a ï¬nal sample
period of 16 ATD clocks.
A.2.2 Factors inï¬uencing accuracy
Three factors â source resistance, source capacitance and current injection â have an inï¬uence on the
accuracy of the ATD.
A.2.2.1 Source Resistance:
Due to the input pin leakage current as speciï¬ed in Table A-6 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
speciï¬es 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 allowed.
MC9S12HZ256 Data Sheet, Rev. 2.05
632
Freescale Semiconductor
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