Appendix B ADC Electricals
S12ZVHY/S12ZVHL Family Reference Manual Rev. 1.05
790
Freescale Semiconductor
B.1.1.1
Port AD Output Drivers Switching
PortAD output drivers switching can adversely affect the ADC accuracy whilst converting the analog
voltage on other PortAD pins because the output drivers are supplied from the VDDA/VSSA ADC supply
pins. Although internal design measures are implemented to minimize the affect of output driver noise, it
is recommended to configure PortAD pins as outputs only for low frequency, low load outputs. The impact
on ADC accuracy is load dependent and not specified. The values specified are valid under condition that
no PortAD output drivers switch during conversion.
B.1.1.2
Source Resistance
Due to the input pin leakage current as specified in conjunction with the source resistance there will be a
voltage drop from the signal source to the ADC input. The maximum source resistance R
S
specifies results
in an error (10-bit resolution) of less than 1/2 LSB (2.5 mV) at the maximum leakage current.
B.1.1.3
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
).
B.1.1.4
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 0x3FF (in 10-bit mode) for analog inputs greater than V
RH
and 0x000 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 B-2. ADC Electrical Characteristics
Supply voltage 3.13 V < V
DDA
< 5.5 V, -40
o
C < TJ < 150
o
C
Num C
Rating
Symbol
Min
Typ
Max
Unit
1
C Max input source resistance
R
S
—
—
10
K
2
D Total input capacitance Non sampling
Total input capacitance Sampling
C
INN
C
INS
—
—
—
—
10
16
pF
3
D
Input internal Resistance
R
INA
-
5
15
k
4
C Disruptive analog input current
I
NA
-2.5
—
2.5
mA
5
C Coupling ratio positive current injection
K
p
—
—
1E-4
A/A
6
C Coupling ratio negative current injection
K
n
—
—
5E-3
A/A
Содержание MC9S12ZVHL32
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Страница 788: ...Appendix A MCU Electrical Specifications S12ZVHY S12ZVHL Family Reference Manual Rev 1 05 788 Freescale Semiconductor...
Страница 794: ...Appendix B ADC Electricals S12ZVHY S12ZVHL Family Reference Manual Rev 1 05 794 Freescale Semiconductor...
Страница 798: ...Appendix D IRC Electrical Specifications S12ZVHY S12ZVHL Family Reference Manual Rev 1 05 798 Freescale Semiconductor...
Страница 802: ...Appendix F MSCAN Electrical Specifications S12ZVHY S12ZVHL Family Reference Manual Rev 1 05 802 Freescale Semiconductor...
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Страница 822: ...Appendix L SPI Electrical Specifications S12ZVHY S12ZVHL Family Reference Manual Rev 1 05 822 Freescale Semiconductor...
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