HD6433045 HITACHI [Hitachi Semiconductor], HD6433045 Datasheet - Page 553

• Manufacturer Part Number: HD6433045
• Description: Hitachi Single-Chip Microcomputer
• Manufacturer: HITACHI [Hitachi Semiconductor]

8. Allowable Signal-Source Impedance: The analog inputs of the H8/3048 Series are designed
9. Effect on Absolute Accuracy: Attaching an external capacitor creates a coupling with ground,
Digital
output
If a large external capacitor is provided in scan mode, then the internal 10-kΩ input resistance
A large external capacitor, however, acts as a low-pass filter. This may make it impossible to
If a filter circuit is used, be careful of interference with digital signals on the same board, and
to assure accurate conversion of input signals with a signal-source impedance not exceeding
10 kΩ. The reason for this rating is that it enables the input capacitor in the sample-and-hold
circuit in the A/D converter to charge within the sampling time. If the sensor output
impedance exceeds 10 kΩ, charging may be inadequate and the accuracy of A/D conversion
cannot be guaranteed.
becomes the only significant load on the input. In this case the impedance of the signal source
is not a problem.
track analog signals with high dv/dt (e.g. a variation of 5 mV/µs) (figure 15-11). To convert
high-speed analog signals or to use scan mode, insert a low-impedance buffer.
so if there is noise on the ground line, it may degrade absolute accuracy. The capacitor must
be connected to an electrically stable ground, such as AV
make sure the circuit does not act as an antenna.
characteristic
conversion
Ideal A/D
Offset error
Actual A/D conversion
characteristic
Figure 15-10 A/D Converter Accuracy Definitions (2)
Nonlinearity
error
Analog input
voltage
Full-scale
error
FS
543
SS
.