13-80
MPC561/MPC563 Reference Manual
MOTOROLA
QADC64E Integration Requirements
operating temperatures. In the temperature range from 125° C to 50° C, the leakage current
is halved for every 8 – 12° C reduction in temperature.
Assuming V
RH – VRL = 5.12 V, one count (assuming 10-bit resolution) corresponds to 5 mV
of input voltage. A typical input leakage of 200 nA acting through 10 k
of external series
resistance results in an error of 0.4 count (2.0 mV). If the source impedance is 100 k
and
a typical leakage of 100 nA is present, an error of two counts (10 mV) is introduced.
In addition to internal junction leakage, external leakage (e.g., if external clamping diodes
are used) and charge sharing effects with internal capacitors also contribute to the total
leakage current.
Table 13-25 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 below 200 nA is obtainable only within
a limited temperature range.
13.7.5.4 Accommodating Positive/Negative Stress Conditions
Positive or negative stress refers to conditions which exceed nominally defined operating
limits. Examples include applying a voltage exceeding the normal limit on an input (for
example, voltages outside of the suggested supply/reference ranges) or causing currents
into or out of the signal which exceed normal limits. QADC64E specific considerations are
voltages greater than V
DDA, VRH or less than VSSA applied to an analog input which cause
Either stress condition can potentially disrupt conversion results on neighboring inputs.
Parasitic devices, associated with CMOS processes, can cause an immediate disruptive
influence on neighboring signals. Common examples of parasitic devices are diodes to
substrate and bipolar devices with the base terminal tied to substrate (V
SSI/VSSA ground).
Under stress conditions, current injected on an adjacent signal can cause errors on the
selected channel by developing a voltage drop across the selected channel’s impedances.
Table 13-25. Error Resulting from Input Leakage (IOFF)
Source
Impedance
Leakage Value (10-bit Conversions)
100 nA
200 nA
500 nA
1000 nA
1 k
—
0.1 counts
0.2 counts
10 k
0.2 counts
0.4 counts
1 counts
2 counts
100 k
2 counts
4 count
10 counts
20 counts