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Section 21 A/D Converter
Rev. 4.00 Sep. 14, 2005 Page 815 of 982
REJ09B0023-0400
21.6 Usage
Notes
When using the A/D converter, note the following points.
21.6.1
Setting Analog Input Voltage
Permanent damage to the LSI may result if the following voltage ranges are exceeded.
1. Analog input range: During A/D conversion, voltages on the analog input pins ANn should not
go beyond the following range: AVss
≤
ANn
≤
AVcc (n = 0 to 7).
2. AVcc and AVss input voltages: Input voltages AVcc and AVss should be VccQ
−
0.2 V
≤
AVcc
≤
VccQ and AVss = Vss. Do not leave the AVcc and AVss pins open when the A/D
converter is not in use and during periods in standby mode; in these situations, connect AVcc
to the power supply (VccQ) and AVss to the ground (VssQ).
21.6.2
Processing of Analog Input Pins
To prevent damage from voltage surges at the analog input pins (AN0 to AN7), connect an input
protection circuit like the one shown in figure 21.7. The circuit shown also includes an RC filter to
suppress noise. This circuit is shown as an example; the circuit constants should be selected
according to actual application conditions. Section 25.4, A/D Converter Characteristics in section
25, Electrical Characteristics shows the analog input pin specifications and figure 21.8 shows an
equivalent circuit diagram of the analog input ports.
21.6.3 Permissible
Signal Source Impedance
This LSI's analog input is designed such that conversion precision is guaranteed for an input signal
for which the signal source impedance is 5k
Ω
or less. This specification is provided to enable the
A/D converter's sample-and-hold circuit input capacitance to be charged within the sampling time;
if the sensor output impedance exceeds 5k
Ω
, charging may be insufficient and it may not be
possible to guarantee A/D conversion precision. However, for A/D conversion in single mode with
a large capacitance provided externally for A/D conversion in single mode, the input load will
essentially comprise only the internal input resistance of 3k
Ω
, and the signal source impedance is
ignored. However, as a low-pass filter effect is obtained in this case, it may not be possible to
follow an analog signal with a large differential coefficient (e.g., 5mV/
µ
s or greater) (see
figure 21.9). When converting a high-speed analog signal, a low-impedance buffer should be
inserted.
Содержание HD6417641
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Страница 11: ...Rev 4 00 Sep 14 2005 Page xi of l USB Universal serial bus WDT Watch dog timer...
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Страница 204: ...Section 4 Clock Pulse Generator CPG Rev 4 00 Sep 14 2005 Page 154 of 982 REJ09B0023 0400...
Страница 212: ...Section 5 Watchdog Timer WDT Rev 4 00 Sep 14 2005 Page 162 of 982 REJ09B0023 0400...
Страница 228: ...Section 6 Power Down Modes Rev 4 00 Sep 14 2005 Page 178 of 982 REJ09B0023 0400...
Страница 246: ...Section 8 X Y Memory Rev 4 00 Sep 14 2005 Page 196 of 982 REJ09B0023 0400...
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Страница 454: ...Section 12 Bus State Controller BSC Rev 4 00 Sep 14 2005 Page 404 of 982 REJ09B0023 0400...
Страница 500: ...Section 13 Direct Memory Access Controller DMAC Rev 4 00 Sep 14 2005 Page 450 of 982 REJ09B0023 0400...
Страница 504: ...Section 14 U Memory Rev 4 00 Sep 14 2005 Page 454 of 982 REJ09B0023 0400...
Страница 566: ...Section 17 Compare Match Timer CMT Rev 4 00 Sep 14 2005 Page 516 of 982 REJ09B0023 0400...
Страница 734: ...Section 18 Multi Function Timer Pulse Unit MTU Rev 4 00 Sep 14 2005 Page 684 of 982 REJ09B0023 0400...
Страница 868: ...Section 21 A D Converter Rev 4 00 Sep 14 2005 Page 818 of 982 REJ09B0023 0400...
Страница 914: ...Section 23 I O Ports Rev 4 00 Sep 14 2005 Page 864 of 982 REJ09B0023 0400...
Страница 956: ...Section 24 List of Registers Rev 4 00 Sep 14 2005 Page 906 of 982 REJ09B0023 0400...
Страница 1016: ...Section 25 Electrical Characteristics Rev 4 00 Sep 14 2005 Page 966 of 982 REJ09B0023 0400...
Страница 1024: ...Appendix Rev 4 00 Sep 14 2005 Page 974 of 982 REJ09B0023 0400...
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