MC9S12DT128CPVE Datasheet, PDF (98/128 Pages) Freescale Semiconductor, Inc – Device User Guide

MC9S12DT128B Device User G^Fu^rid^ee^e—^sV^c0^a1.^l0^e9 ^{Semiconductor, Inc.}
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.
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, C_f ≥ 1024 * (C_INS– C_INN).
A.2.2.3 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 $3FF ($FF in 8-bit mode) for analog inputs greater than V_RH and $000 for values less than
V_RL unless the current is higher than specified as disruptive conditions.
2. Current is injected into pins in the neighborhood of the channel being converted. A portion of this
current is picked up by the channel (coupling ratio K), This additional current impacts the accuracy
of the conversion depending on the source resistance.
The additional input voltage error on the converted channel can be calculated as V_ERR = K * R_S *
I_INJ, with I_INJ being the sum of the currents injected into the two pins adjacent to the converted
channe
Table A-9 ATD Electrical Characteristics
Conditions are shown in Table A-4 unless otherwise noted
Num C
Rating
Symbol Min
Typ
Max
Unit
1 C Max input Source Resistance
R_S
-
-
1
KΩ
Total Input Capacitance
2 T Non Sampling
Sampling
C_INN
C_INS
10
pF
22
3 C Disruptive Analog Input Current
I_NA
-2.5
2.5
mA
4 C Coupling Ratio positive current injection
K_p
10^-4
A/A
5 C Coupling Ratio negative current injection
K_n
10^-2
A/A
For More Information On This Product,
Go to: www.freescale.com