MC9S12E256 Datasheet, PDF (586/602 Pages) Freescale Semiconductor, Inc – HCS12 Microcontrollers

Appendix A Electrical Characteristics
Table A-20. 3.3V ATD Operating Characteristics
Conditions are shown in Table A-4 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
V_RL
V_SSA
—
V_DDA/2
V
High V_RH
V_DDA/2
—
V_DDA
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 Cycles¹ N_CONV10
14
—
28
Cycles
Conv, Time at 2.0MHz ATD Clock f_ATDCLK T_CONV10
7
—
14
µs
Conv, Time at 4.0MHz² ATD Clock f_ATDCLK T_CONV10
3.5
—
7
µs
5 D ATD 8-Bit Conversion Period
Clock Cycles¹ N_CONV8
12
—
26
Cycles
Conv, Time at 2.0MHz ATD Clock f_ATDCLK T_CONV8
6
—
13
µs
6 D Recovery Time (V_DDA=3.3 Volts)
t_REC
—
—
20
µs
7 P Reference Supply current
I_REF
—
—
0.250
mA
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.
2 _{Reduced accuracy see Table A-22 and Table A-23.}
A.6.3 Factors Influencing Accuracy
Three factors — source resistance, source capacitance and current injection — have an influence on the
accuracy of the ATD.
A.6.3.1 Source Resistance
Due to the input pin leakage current as specified in Table A-6 and 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 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 are allowed.
A.6.3.2 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).
A.6.3.3 Current Injection
There are two cases to consider.
1. A current is injected into the channel being converted. The channel being stressed has conversion
values of 0x3FF (0xFF in 8-bit mode) for analog inputs greater than VRH and 0x000 for values
less than VRL unless the current is higher than specified as disruptive conditions.
MC9S12E256 Data Sheet, Rev. 1.08
586
Freescale Semiconductor