SH7052 datasheet(613/919 Pages) RENESAS

613 / 919 page

587

4. Notes on board design

In board design, digital circuitry and analog circuitry should be as mutually isolated as

possible, and layout in which digital circuit signal lines and analog circuit signal lines cross or

are in close proximity should be avoided as far as possible. Failure to do so may result in

incorrect operation of the analog circuitry due to inductance, adversely affecting A/D

conversion values.

Also, digital circuitry must be isolated from the analog input signals (ANn), analog reference

voltage (AV

ref), and analog power supply (AVCC) by the analog ground (AVSS). AVSS should be

connected at one point to a stable digital ground (V

SS) on the board.

5. Notes on noise countermeasures

A protection circuit connected to prevent damage due to an abnormal voltage such as an

excessive surge at the analog input pins (ANn) and analog reference voltage (AV

ref) should be

connected between AV

CC and AVSS as shown in figure 16.8.

Also, the bypass capacitors connected to AV

CC and AVref and the filter capacitor connected to

ANn must be connected to AV

SS. If a filter capacitor is connected as shown in figure 16.8, the

input currents at the analog input pins (ANn) are averaged, and so an error may arise. Careful

consideration is therefore required when deciding the circuit constants.

AVCC

AVref

AN0–AN31

AVSS

SH7052

SH7053

SH7054

Notes:

µF

0.01

µF

Rin*

0.1

µF

100

Ω

2. Rin: Input impedance

Figure 16.8 Example of Analog Input Pin Protection Circuit

SH7052 Datasheet(PDF) 613 Page - Renesas Technology Corp

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