MC9S12NE64V1 Datasheet, PDF (513/554 Pages) Freescale Semiconductor, Inc – MC9S12NE64V1 Data Sheet

ATD Electrical Characteristics
A.11.2.2 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.11.2.3 Current Injection
There are two cases to consider.
• 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 VRH and $000 for values less
than VRL unless the current is higher than specified as disruptive conditions.
• 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-9. ATD Electrical Characteristics
Conditions are shown in Table A-4 unless otherwise noted
Num C
Rating
1
C Max input Source Resistance
2
T Total Input Capacitance
Non Sampling
Sampling
3
C Disruptive Analog Input Current
4
C Coupling Ratio positive current injection
5
C Coupling Ratio negative current injection
Symbol Min Typ Max Unit
R_S
C_INN
C_INS
I_NA
K_p
K_n
—
—
–2.5
1
kΩ
pF
10
15
2.5
mA
10^-4
A/A
10^-2
A/A
A.11.3 ATD Accuracy — 3.3 V Range
Table A-10 specifies the ATD conversion performance excluding any errors due to current injection, input
capacitance and source resistance.
MC9S12NE64 Data Sheet, Rev. 1.1
Freescale Semiconductor
513