Appendix A Electrical Characteristics
Freescale Semiconductor
MC9S12C-Family / MC9S12GC-Family
659
Rev 01.24
A.2.2
ATD Operating Characteristics In 3.3V Range
The
shows conditions under which the ATD operates.
The following constraints exist to obtain full-scale, full range results: V
SSA
≤
V
RL
≤
V
IN
≤
V
RH
≤
V
DDA
.
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.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
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 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, C
f
≥
1024 * (C
INS
– C
INN
).
Table A-11. ATD Operating Characteristics
Conditions are shown in
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
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.
N
CONV10
T
CONV10
14
7
—
—
28
14
Cycles
µ
s
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
µ
s
6
D Recovery Time (V
DDA
=3.3 Volts)
t
REC
—
—
20
µ
s
7
P Reference Supply current
I
REF
—
—
0.250
mA
Summary of Contents for MC9S12C Family
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