S9S12G128F0CLF Datasheet, PDF (1085/1158 Pages) Freescale Semiconductor, Inc – MC9S12G Family Reference Manual

Electrical Characteristics
A.4.2.3 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 (10-bit resilution), then the external filter capacitor, C_f ≥ 1024 * (C_INS–C_INN).
A.4.2.4 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 (in 10-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 condition.
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 channel.
Table A-15. ADC Electrical Characteristics
Supply voltage 3.13 V < V_DDA < 5.5 V, -40^oC < T_J < 150^oC
Num C
Rating
Symbol
Min
1 C Max input source resistance¹
2 D Total input capacitance Non sampling
Total input capacitance Sampling
3 D Input internal Resistance
R_S
—
C_INN
—
C_INS
—
R_INA
-
4 C Disruptive analog input current
I_NA
-2.5
5 C Coupling ratio positive current injection
K_p
—
6 C Coupling ratio negative current injection
K_n
—
1 _{1 Refer to A.4.2.2 for further information concerning source resistance}
Typ
Max
Unit
—
1
KΩ
—
10
pF
—
16
5
15
kΩ
—
2.5
mA
—
1E-4
A/A
—
5E-3
A/A
A.4.3 ADC Accuracy
Table A-16 and Table A-18 specifies the ADC conversion performance excluding any errors due to
current injection, input capacitance and source resistance.
Freescale Semiconductor
MC9S12G Family Reference Manual, Rev.1.10
1085