H8SXSLASH1663M datasheet(1126/1504 Pages) RENESAS

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Section 22 A/D Converter

Rev. 2.00 Sep. 24, 2008 Page 1094 of 1468

REJ09B0412-0200

provided externally for conversion in single mode, the input load will essentially comprise only

the internal input resistance of 10 k

Ω, and the signal source impedance is ignored. However, since

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., 5 mV/

µs or greater) (see figure 22.12). When converting

a high-speed analog signal or conversion in scan mode, a low-impedance buffer should be

inserted.

Equivalent circuit of the A/D converter

This LSI

20 pF

Cin =

15 pF

10 k

Ω

Low-pass

filter

C = 0.1

µF

(recommended value)

Sensor output

impedance

≤ 5 kΩ

Sensor input

Figure 22.12 Example of Analog Input Circuit

22.7.5

Influences on Absolute Accuracy

Adding capacitance results in coupling with GND, and therefore noise in GND may adversely

affect absolute accuracy. Be sure to make the connection to an electrically stable GND such as

AVss.

Care is also required to insure that filter circuits do not communicate with digital signals on the

mounting board, acting as antennas.

22.7.6

Setting Range of Analog Power Supply and Other Pins

If the conditions shown below are not met, the reliability of the LSI may be adversely affected.

• Analog input voltage range

The voltage applied to analog input pin ANn during A/D conversion should be in the range

AVss

≤ VAN ≤ Vref.

• Relation between AVcc, AVss and Vcc, Vss

As the relationship between AVcc, AVss and Vcc, Vss, set AVcc = Vcc

± 0.3 V and AVss =

Vss. If the A/D converter is not used, set AVcc = Vcc and AVss = Vss.

• Vref setting range

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