APPENDIX C MOUNTING PRECAUTIONS
S1C17F13 TeChniCal Manual
Seiko epson Corporation
aP-C-1
(Rev. 1.0)
V
DD
V
SS
V
DD
V
SS
Bypass capacitor
connection example
C
PW1
C
PW1
Appendix C Mounting Precautions
This section describes various precautions for circuit board design and IC mounting.
Oscillator circuit
• Oscillation characteristics depend on factors such as components used (resonator, C
G
, C
D
) and circuit board
patterns. In particular, with crystal resonators, select the appropriate capacitors (C
G
, C
D
) only after fully
evaluating components actually mounted on the circuit board.
• Oscillator clock disturbances caused by noise may cause malfunctions. To prevent such disturbances, con-
sider the following points.
(1) Components such as a resonator, resistors, and capacitors connected to the OSC1 (OSC3) and OSC2 (OSC4)
pins should have the shortest connections possible.
(2) Wherever possible, avoid locating digital signal lines within 3 mm of the OSC1 (OSC3) and OSC2 (OSC4)
pins or related circuit components and wiring. Rapidly-switching signals, in particular, should be kept at a
distance from these components. Since the spacing between layers of multi-layer printed circuit boards is
a mere 0.1 mm to 0.2 mm, the above precautions also apply when positioning digital signal lines on other
layers.
Never place digital signal lines alongside such components or wiring, even if more than 3 mm distance or
located on other layers. Avoid crossing wires.
(3) Use V
SS
to shield OSC1 (OSC3) and OSC2 (OSC4) pins and related
wiring (including wiring for adjacent circuit board layers). Layers wired
should be adequately shielded as shown to the right. Fully ground adja-
cent layers, where possible. At minimum, shield the area at least 5 mm
around the above pins and wiring.
Even after implementing these precautions, avoid configuring digital
signal lines in parallel, as described in (2) above. Avoid crossing even
on discrete layers, except for lines carrying signals with low switching
frequencies.
(4) After implementing these precautions, check the FOUT pin output clock
waveform by running the actual application program within the product.
For OSC3ACLK, confirm that the frequency is as designed, is free of noise, and has minimal jitter.
For OSC1CLK, in particular, enlarge the areas before and after the clock rising and falling edges and take
special care to confirm that the regions approximately 100 ns to either side are free of clock or spiking
noise.
Failure to observe precautions (1) to (3) adequately may lead to jitter in OSC3ACLK and noise in the OSC-
1CLK. Jitter in OSC3ACLK will reduce operating frequencies, while noise in the OSC1CLK will destabi-
lize timers that use OSC1CLK as well as CPU Core operations.
#RESET pin
Components such as a switch and resistor connected to the #RESET pin should have the shortest connections
possible to prevent noise-induced resets.
Power supply circuit
Sudden power supply fluctuations due to noise will cause malfunctions. Consider the following issues.
(1) Connections from the power supply to the V
DD
and V
SS
pins should be
implemented via the shortest, thickest patterns possible.
(2) If a bypass capacitor is connected between V
DD
and V
SS
, connections
between the V
DD
and V
SS
pins should be as short as possible.
Sample
V
SS
pattern
(OSC1)
OSC1
OSC2
V
SS