SH7721 datasheet(1011/1524 Pages) RENESAS

1011 / 1524 page

Section 27

A/D Converter

Rev. 3.00

Jan. 18, 2008

Page 949 of 1458

REJ09B0033-0300

27.7.4

Influence to Absolute Accuracy

By adding capacitance, absolute accuracy may be degraded if noise is on GND because there is

coupling with GND. Therefore, connect electrically stable GND such as AVss to prevent absolute

accuracy from being degraded.

A filter circuit must not interfere with digital signals, or must not be an antenna on a mounting

board.

20 pF

Cin =

15 pF

3 k

Ω

to 5 k

Ω

Output impedance of sensor

Sensor input

This LSI

Lowpass

filter

(C = 0.1

µF)

Equivalent circuit

of A/D converter

Figure 27.8

Analog Input Circuit Example

27.7.5

Setting Analog Input Voltage

Operating the chip in excess of the following voltage range may result in damage to chip

reliability.

During A/D conversion, the voltages (VANn) input to the analog input pins ANn should be in the

range AV

SS ≤ VANn ≤ AVCC (n = 0 to 3).

27.7.6

Notes on Board Design

In designing a board, separate digital circuits and analog circuits. Do not intersect or locate closely

signal lines of a digital circuit and an analog circuit. An analog circuit may malfunction due to

induction, thus affecting A/D conversion values. Separate analog input pins (AN0 to AN3) and the

analog power voltage (AVcc) from digital circuits with analog ground (AVss). Connect analog

ground (AVss) to one point of stable ground (Vss) on the board.

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