USB controller
FS/LS
transceiver
USB voltage
regulator
D+ D-
VREGIN VOUT33
Figure 3-28. USB Subsystem Overview
3.9.1.1 USB Wakeup
When the USB detects that there is no activity on the USB bus for more than 3 ms, the
INT_STAT[SLEEP] bit is set. This bit can cause an interrupt and software decides the
appropriate action.
Waking from a low power mode (except in LLS/VLLS mode where USB is not powered)
occurs through an asynchronous interrupt triggered by activity on the USB bus. Setting
the USBTRC0[USBRESMEN] bit enables this function.
3.9.1.2 USB Power Distribution
This chip includes an internal 5 V to 3.3 V USB regulator that powers the USB
transceiver or the MCU (depending on the application).
3.9.1.2.1 AA/AAA cells power supply
The chip can be powered by two AA/AAA cells. In this case, the MCU is powered
through VDD which is within the 1.8 to 3.0 V range. After USB cable insertion is
detected, the USB regulator is enabled to power the USB transceiver.
Communication interfaces
KL25 Sub-Family Reference Manual, Rev. 3, September 2012
92 Freescale Semiconductor, Inc.
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