APPENDIX C MOUNTING PRECAUTIONS
S1C33L26 TECHNICAL MANUAL
Seiko Epson Corporation
AP-C-3
Precautions on VBUS
Be sure to not apply 6 V (max.) or more to the VBUS pin as the IC may be destroyed.
It is especially necessary to suppress overshoot on the input voltage and to prevent the host power source
becoming unstable when the USB cable is plugged into the connector. The figure below shows an example
of external connection.
USBDP
USBDM
USBVBUS
DP
DM
VBUS
S1C33L26
R1
C1
Pull down the USBVBUS, USBDP, and USBDM pins when the USB is not used.
Receptor
C1: 1
µ
F
R1: 10
W
In addition to the above, verify the VBUS state completely on the actual circuit board using an oscilloscope
or other device. Overshoot and other symptoms are more likely to occur when using a long USB cable and
connecting it to the host side connector.
Precautions on DP and DM
When designing a printed circuit board, observe the following precautions to ensure that both DP and DM
signals are properly routed:
• To prevent signal skew and to stabilize differential impedance, the DP and DM signal lines must be
routed in parallel and in the same length, with the pins and connector connected in the shortest distance
possible. Crossed wiring of these signals should be avoided as much as possible.
• The periphery of these signal lines must be enclosed by a GND pattern, and with the GND pattern also
created for the internal layer immediately below that. In particular, the routing of high-speed digital sig-
nal lines parallel to or across these signal lines should be avoided as much as possible.
We recommend that you verify the EYE pattern on the actual circuit board.
Noise-induced malfunctions
Check the following five points if you suspect the presence of noise-induced IC malfunctions.
(1) TEST pin
If this pin is exposed to high-level noise, the entire IC enters test mode or a high-impedance state and be-
comes inoperable. In such cases, the IC will not be restored, even when the pin is returned to a low level.
Therefore, always make sure the TEST pin is connected to GND on the circuit board. Although the IC con-
tains internal pull-down resistors, it is susceptible to noise because these resistors are high impedance (ap-
proximately 50 to 100 k
W
).
(2) DSIO pin
Low-level noise to this pin will cause a switch to debug mode. The switch to debug mode can be confirmed
by the clock output from DCLK and a High signal from the DST2 pin.
For the product version, we recommend connecting the DSIO pin directly to HV
DD
or pulling up the DISO
pin using a resistor not exceeding 10 k
W
. The IC includes an internal pull-up resistor. The resistor has a
relatively high impedance of 100 k
W
to 500 k
W
and is not noise-resistant.
(3) #RESET pin
Low-level noise to this pin will reset the IC. Depending on the input waveform, the reset may not proceed
correctly. This is more likely to occur if, due to circuit design choices, the impedance is high when the reset
input is high.