
Appendix A Electrical Characteristics
MC9S12XDP512 Data Sheet, Rev. 2.21
1254
Freescale Semiconductor
Table A-13. ATD Operating Characteristics 3.3V
A.2.2
Factors Inuencing Accuracy
Three factors — source resistance, source capacitance and current injection — have an inuence on the
accuracy of the ATD.
A.2.2.1
Source Resistance
Due to the input pin leakage current as specied 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
species results in an error of less than 1/2 LSB (2.5 mV) 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.
A.2.2.2
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 lter capacitor, Cf ≥ 1024 * (CINS–CINN).
Conditions are shown in
Table A-4 unless otherwise noted, Supply Voltage 3.15V < VDDA < 3.6V
Num
C
Rating
Symbol
Min
Typ
Max
Unit
1
D Reference potential
Low
High
VRL
VRH
VSSA
VDDA/2
—
VDDA/2
VDDA
V
2
C Differential reference voltage1
1 Full accuracy is not guaranteed when differential voltage is less than 3.15 V
VRH-VRL
3.15
3.3
3.6
V
3
D ATD clock frequency
fATDCLK
0.5
—
2.0
MHz
4
D ATD 10-bit conversion period
Clock cycles2
Conv, time at 2.0 MHz ATD clock fATDCLK
2 The minimum time assumes a nal sample period of 2 ATD clocks cycles while the maximum time assumes a nal sample
period of 16 ATD clocks.
NCONV10
TCONV10
14
7
—
28
14
Cycles
s
5
D ATD 8-bit conversion period
Clock cycles2
Conv, time at 2.0 MHz ATD clock fATDCLK
NCONV8
TCONV8
12
6
—
26
13
Cycles
s
6
D Recovery time (VDDA = 5.0 Volts)
tREC
——
20
s
7
P Reference supply current 2 ATD blocks on
IREF
—
0.500
mA
8
P Reference supply current 1 ATD block on
IREF
—
0.250
mA