Lucent Technologies MN10285K - Manual (Page 153)

Analog-to-Digital Converter
Cautions about Analog-to-Digital Converter
Panasonic Semiconductor Development Company MN102H75K/F75K/85K/F85K LSI User Manual
152
Panasonic
6.7 Cautions about Analog-to-Digital Converter
The type of this Analog-to-Digital Converter is a sample-hold one, and so the
current temporarily flows in conversion to charge the condenser of the sample-
hold circuit. For this reasons, the following settings are needed to get the
accurancy of convension:
1. Impedance of analog input terminal must be below 8k
Ω
.
2. When impedance of analog input terminal is over 8k
Ω
, condenser which
capacity is above 2000 pF must be connected to suppress the voltage
changes of the analog input terminal.
3. During conversion do not change the output level of the terminal (from H to
L or from L to H), and not turn on and off the peripheral circuit, cause these
actions may influence the power supply voltage.
Figure 6-12 Cautions on Analog-to-Digital Converter
micro computer
analog signal output
equivalent circuit
Analog-to-Digital
input terminal
R
C
Vss
R << 8k Ω
or
C
≥
2000pF