Appendix A Electrical Characteristics
MC9S12XDP512 Data Sheet, Rev. 2.11
Freescale Semiconductor 933
Table A-13. ATD Operating Characteristics 3.3V
A.2.2 Factors Influencing Accuracy

Three factors — source resistance, source capacitance and current injection — have an influence on the

accuracy of the ATD.

A.2.2.1 Source Resistance

Due to the input pin leakage current as specified 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

specifies 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 filter 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
V
2 C Differential reference voltage1
1Full 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
2The 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.
NCONV10
TCONV10
14
7
28
14
Cycles
µs
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
µs
6 D Recovery time (VDDA = 5.0 Volts) tREC ——20µs
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