mc9s12xs128 Freescale Semiconductor, Inc, mc9s12xs128 Datasheet - Page 674

• Manufacturer Part Number: mc9s12xs128
• Description: Hcs12 Microcontrollers 16-bit Automotive Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Electrical Characteristics
is recommended to configure PortAD pins as outputs only for low frequency, low load outputs. The impact
on ATD accuracy is load dependent and not specified. The values specified are valid under condition that
no PortAD output drivers switch during conversion.
A.2.2.2
Due to the input pin leakage current as specified in
resistance there will be a voltage drop from the signal source to the ATD input. The maximum source
resistance R
leakage current. If device or operating conditions are less than worst case or leakage-induced error is
acceptable, larger values of source resistance of up to 10Kohm are allowed.
A.2.2.3
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
A.2.2.4
There are two cases to consider.
674
1. A current is injected into the channel being converted. The channel being stressed has conversion
2. Current is injected into pins in the neighborhood of the channel being converted. A portion of this
values of $3FF (in 10-bit mode) for analog inputs greater than V
V
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:
with I
RL
S
unless the current is higher than specified as disruptive condition.
INJ
Source Resistance
Source Capacitance
Current Injection
specifies results in an error (10-bit resolution) of less than 1/2 LSB (2.5 mV) at the maximum
V
being the sum of the currents injected into the two pins adjacent to the converted channel.
ERR
= K * R
S
* I
S12XS Family Reference Manual, Rev. 1.10
INJ
Table A-7
and
Table A-8
f
≥ 1024 * (C
RH
in conjunction with the source
and $000 for values less than
INS
Freescale Semiconductor
–C
INN
).