MC9S12HZ256 Datasheet, PDF (632/692 Pages) Freescale Semiconductor, Inc – HCS12 Microcontrollers

Appendix A Electrical Characteristics
A.2 ATD
This section describes the characteristics of the analog to digital converter.
A.2.1 ATD Operating Characteristics
The Table A-8 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.
Table A-8. ATD Operating Characteristics
Conditions are shown in Table A-4 unless otherwise noted
Num C
Rating
Symbol
Min
Typ
Max
Unit
1 D Reference Potential
2 C Differential Reference Voltage¹
Low
High
V_RL
V_RH
V_RH–V_RL
V_SSA
V_DDA/2
4.50
5.00
V_DDA/2
V
V_DDA
V
5.25
V
3 D ATD Clock Frequency
f_ATDCLK
0.5
2.0
MHz
4 D ATD 10-Bit Conversion Period
Clock Cycles^{2 N}CONV10
14
Conv, Time at 2.0MHz ATD Clock f_ATDCLK ^TCONV10
7
28
Cycles
14
µs
5 D ATD 8-Bit Conversion Period
Clock Cycles^{2 N}CONV8
12
Conv, Time at 2.0MHz ATD Clock f_ATDCLK ^TCONV8
6
26
Cycles
13
µs
6 D Stop Recovery Time (V_DDA=5.0 Volts)
t_SR
20
µs
7 P Reference Supply current
I_REF
0.375
mA
1 _{Full accuracy is not guaranteed when differential voltage is less than 4.50V}
2 _{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.
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-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 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 allowed.
MC9S12HZ256 Data Sheet, Rev. 2.04
632
Freescale Semiconductor