
Appendix A Electrical Characteristics
Freescale Semiconductor
MC9S12Q128
611
Rev 1.10
A.2.2
ATD Operating Characteristics In 3.3V Range
The
Table A-11 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 amplier 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.2.3
Factors Inuencing Accuracy
Three factors — source resistance, source capacitance and current injection — have an inuence on the
accuracy of the ATD.
A.2.3.1
Source Resistance
Due to the input pin leakage current as specied 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
species 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 lter capacitor, Cf ≥ 1024 * (CINS – CINN).
Table A-11. 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
1D
Reference Potential
Low
High
VRL
VRH
VSSA
VDDA/2
—
VDDA/2
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
4D
ATD 10-Bit Conversion Period
Clock Cycles(1)
Conv, Time at 2.0MHz ATD Clock fATDCLK
1. 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
5D
ATD 8-Bit Conversion Period
Clock Cycles1
Conv, Time at 2.0MHz ATD Clock fATDCLK
NCONV8
TCONV8
12
6
—
26
13
Cycles
s
6
D Recovery Time (VDDA=3.3 Volts)
tREC
——
20
s
7
P Reference Supply current
IREF
—
0.250
mA