APPENDIX C MOUNTING PRECAUTIONS
S1C33L26 TECHNICAL MANUAL
Seiko Epson Corporation
AP-C-1
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, R
f
, C
G
, C
D
) and circuit
board patterns. In particular, with ceramic or crystal resonators, select the appropriate external resistor (R
f
)
and 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, consid-
er the following points. The latest devices, in particular, are manufactured by microscopic processes, making
them especially susceptible to noise.
Areas in which noise countermeasures are especially important include the RTCCLKO pin and related circuit
components and wiring. RTCCLKI pin handling is equally important. The noise precautions required for the
RTCCLKI and RTCCLKO pins are described below. We also recommend applying similar noise countermea-
sures to the high-speed oscillator circuit, such as the MCLKI and MCLKO pins and wiring.
(1) Components such as a resonator, resistors, and capacitors connected to the RTCCLKI (MCLKI) and RTC-
CLKO (MCLKO) pins should have the shortest connections possible.
(2) Wherever possible, avoid locating digital signal lines within 3 mm of the RTCCLKI (MCLKI) and RTC-
CLKO (MCLKO) 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 RTCCLKI (MCLKI) and RTCCLKO (MCLKO) pins and
related wiring (including wiring for adjacent circuit board layers). Layers
wired should be adequately shielded as shown to the right. Fully ground
adjacent 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) When an external clock is supplied to the RTCCLKI or MCLKI pin, the clock source should be connected
to the RTCCLKI or MCLKI pin in the shortest line. Furthermore, do not connect anything else to the RTC-
CLKO or MCLKO pin.
(5) After implementing these precautions, check the output clock waveform by running the actual application
program within the product. Use an oscilloscope to check outputs from the CMU_CLK pin.
You can check the quality of the OSC3 or PLL output waveform via the CMU_CLK output. Confirm that
the frequency is as designed, is free of noise, and has minimal jitter.
You can also check the quality of the OSC1 waveform via the CMU_CLK output. In particular, enlarge the
areas before and after the clock rising and falling edges and take special care to confirm that the regions ap-
proximately 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 the OSC3 or PLL output and noise
in the OSC1 output. Jitter in the OSC3 output will reduce operating frequencies, while noise in the OSC1
output will destabilize timers operated by the OSC1 clock as well as CPU Core operations when the system
clock switches to OSC1.
MCLKI
MCLKO
V
SS
Sample V
SS
pattern (OSC3)