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MC68HC16Z1CPV16 Datasheet, PDF (209/500 Pages) Freescale Semiconductor, Inc – Symbols and Operators, CPU16 Register Mnemonics | |||
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Freescale Semiconductor, Inc.
Table 8-10 External Circuit Settling Time (10-Bit Conversions)
Filter Capacitor
(CF)
1 µF
.1 µF
.01 µF
.001 µF
100 pF
100 â¦
760 µs
76 µs
7.6 µs
760 ns
76 ns
Source Resistance (RF)
1 kâ¦
10 kâ¦
7.6 ms
76 ms
760 µs
7.6 ms
76 µs
760 µs
7.6 µs
76 µs
760 ns
7.6 µs
100 kâ¦
760 ms
76 ms
7.6 ms
760 µs
76 µs
The external circuit described in Table 8-10 is a low-pass filter. A user interested in
measuring an AC component of the external signal must take the characteristics of this
filter into account.
8.8.6.2 Error Resulting from Leakage
A series resistor limits the current to a pin, therefore input leakage acting through a
large source impedance can degrade A/D accuracy. The maximum input leakage cur-
rent is specified in APPENDIX A ELECTRICAL CHARACTERISTICS. Input leakage
is greatest at high operating temperatures and as a general rule decreases by one half
for each 10°C decrease in temperature.
Assuming VRH â VRL = 5.12 V, 1 count (assuming 10-bit resolution) corresponds to 5
mV of input voltage. A typical input leakage of 50 nA acting through 100 k⦠of external
series resistance results in an error of less than 1 count (5.0 mV). If the source imped-
ance is 1 M⦠and a typical leakage of 50 nA is present, an error of 10 counts (50 mV)
is introduced.
In addition to internal junction leakage, external leakage (e.g., if external clamping di-
odes are used) and charge sharing effects with internal capacitors also contribute to
the total leakage current. Table 8-11 illustrates the effect of different levels of total
leakage on accuracy for different values of source impedance. The error is listed in
terms of 10-bit counts.
CAUTION
Leakage from the part of 10 nA is obtainable only within a limited tem-
perature range.
Table 8-11 Error Resulting From Input Leakage (IOFF)
Source
Impedance
1 kâ¦
10 kâ¦
100 kâ¦
10 nA
â
â
0.2 counts
Leakage Value (10-Bit Conversions)
50 nA
100 nA
â
â
0.1 counts
0.2 counts
1 count
2 counts
1000 nA
0.2 counts
2 counts
20 counts
M68HC16 Z SERIES
USERâS MANUAL
ANALOG-TO-DIGITAL CONVERTER
For More Information On This Product,
Go to: www.freescale.com
8-23
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