Datasheet

Appendix A Electrical Characteristics
MC9S12E128 Data Sheet, Rev. 1.07
590 Freescale Semiconductor
A.6.2 ATD Operating Characteristics — 3.3V Range
The Table A-20 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 amplifier 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.
A.6.3 Factors Influencing Accuracy
Three factors — source resistance, source capacitance and current injection — have an influence on the
accuracy of the ATD.
A.6.3.1 Source Resistance
Due to the input pin leakage current as specified in Table A-6 and 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 R
S
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 are allowed.
Table A-20. 3.3V ATD Operating Characteristics
Conditions are shown in Table A-4 unless otherwise noted; Supply Voltage 3.3V-10% <= V
DDA
<= 3.3V+10%
Num C Rating Symbol Min Typ Max Unit
1 D Reference Potential
Low
High
V
RL
V
RH
V
SSA
V
DDA
/2
—
—
V
DDA
/2
V
DDA
V
V
2 C Differential Reference Voltage V
RH
-V
RL
3.0 3.3 3.6 V
3 D ATD Clock Frequency f
ATDCLK
0.5 — 2.0 MHz
4 D ATD 10-Bit Conversion Period
Clock Cycles
1
Conv, Time at 2.0MHz ATD Clock f
ATDCLK
Conv, Time at 4.0MHz
2
ATD Clock f
ATDCLK
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
Reduced accuracy see Table A-22 and Table A-23.
N
CONV10
T
CONV10
T
CONV10
14
7
3.5
—
—
—
28
14
7
Cycles
µs
µs
5 D ATD 8-Bit Conversion Period
Clock Cycles
1
Conv, Time at 2.0MHz ATD Clock f
ATDCLK
N
CONV8
T
CONV8
12
6
—
—
26
13
Cycles
µs
6 D Recovery Time (V
DDA
=3.3 Volts) t
REC
——20µs
7 P Reference Supply current I
REF
— — 0.250 mA