7 PRECAUTIONS ON MOUNTING

7 Precautions on Mounting

The following shows the precautions when designing the board and mounting the IC.

Oscillation Circuit

•Oscillation characteristics change depending on conditions (board pattern, components used, etc.). In particular, when a ceramic oscillator or crystal oscillator is used, use the oscillator manufacturer's recommended values for constants such as capacitance and resistance.

•Disturbances of the oscillation clock due to noise may cause a malfunction. Consider the following points to prevent this:

(1)Components which are connected to the OSC3 (OSC1), OSC4 (OSC2) and PLLC pins, such as oscillators, resistors and capacitors, should be connected in the shortest line.

(2)As shown in the figure below, make a VSS pattern as large as possible at circumscription of the OSC3 (OSC1) and OSC4 (OSC2) pins and the components connected to these pins. The same applies to the PLLC pin.

Furthermore, do not use this VSS pattern to connect other components than the oscillation system.

Sample VSS pattern

OSC3 and OSC4

PLLC

VSS

OSC4

PLLC

OSC3

VSS

VSS

(3)When supplying an external clock to the OSC3 (OSC1) pin, the clock source should be connected to the OSC3 (OSC1) pin in the shortest line.

Furthermore, do not connect anything else to the OSC4 (OSC2) pin.

•In order to prevent unstable operation of the oscillation circuit due to current leak between OSC3 (OSC1) and VDD, please keep enough distance between OSC3 (OSC1) and VDD or other signals on the board pattern.

Reset Circuit

•The power-on reset signal which is input to the #RESET pin changes depending on conditions (power rise time, components used, board pattern, etc.). Decide the time constant of the capacitor and resistor after enough tests have been completed with the application product.

•In order to prevent any occurrences of unnecessary resetting caused by noise during operating, components such as capacitors and resistors should be connected to the #RESET pin in the shortest line.

Power Supply Circuit

•Sudden power supply variation due to noise may cause malfunction. Consider the following points to prevent this:

(1)The power supply should be connected to the VDD, VDDE, VSS and AVDDE pins with patterns as short and large as possible.

In particular, the power supply for AVDDE affects A/D conversion precision.

A-1

A-7

S1C33205 PRODUCT PART

EPSON

A-69