AN663 データシートの表示（PDF） - Silicon Laboratories

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AN663

PRECISION32 MCU FAMILY CLOCKING OPTIONS

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AN663

2.6. USB Oscillator (USBnOSC)

The USB oscillator is part of the USBn module and operates at a factory-calibrated 48 MHz. When connected to

the USB bus, the clock recovery mechanism can constantly adjust the oscillator frequency relative to the full-speed

frame reference, creating a very accurate clock source. This oscillator is within the USB specification across

voltage and temperature, allowing the application system to be hardware USB certified without an external

oscillator. This oscillator can be used as the AHB clock source even if the USB peripheral is not used.

Figure 9 displays the USBn module block diagram.

EXTOSCn

PLLnOSC

D+

D-

USBn Module

Clock Recovery

Internal USBn

Oscillator

USBnOSC

Transceiver

Serial Interface

Engine

Figure 9. USB Module Block Diagram

10

Rev. 0.1

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