Microchip Technology EVB-USB3503 QFN, Руководство пользователя

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EVB-USB3503 QFN Evaluation Board User’s Guide
DS50002252A-page 12
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2014 Microchip Technology Inc.
2.1.3 Clock Source – 26 MHz Oscillator
By default, a 26 MHz oscillator (Y1) is populated on the evaluation board as the clock
source for the USB3503. The REFSEL[1:0] pins are used to select the frequency of the
clock. The board is configured by default to select a 26 MHz clock source by both pull-
ing the REF_SEL0 pin high to +3.3 VDC and pulling the REF_SEL1 pin low to ground.
The USB3503 can accept several clock frequencies. If the clock source on the EVB is
changed, the resistors connected to the REF_SEL[1:0] pins must be reconfigured to
select the appropriate frequency.
Table 2-1 shows the resistors that are required in
order to select the compatible frequency. The location of the resistors on the EVB can
be seen in
Figure 2.1.4 .
FIGURE 2-2: HUB_CONNECT SWITCH POSITIONS
TABLE 2-1: CLOCK FREQUENCY SELECTION RESISTOR CONFIGURATION
REFSEL[1:0] Clock Frequency R18 R21 R27 R30
00 38.4 MHz Empty Empty Install Install
01 26.0 MHz (default) Empty Install Install Empty
10 19.2 MHz Install Empty Empty Install
11 12.0 MHz Install Install Empty Empty