Information

Table 41-13. USB battery charger subsystem components (continued)
Component Description
USB Transceiver The USB transceiver contains the pullup resistor for the USB D+ signal and the pulldown
resistors for the USB D+ and D– signals. The D+ pullup and the D– pulldown are both used
during the charger detection sequence. The USB transceiver also outputs the digital state of
the D+ and D– signals from the USB bus.
The pullup and pulldown enable signals are controlled by other modules during the charger
detection sequence. The D+ pullup enable is output from the USB controller and is under
software control. The USBDCD module controls the D–pulldown enable.
USBDCD Module Detects whether the device has been plugged into either a standard host port, a charging
host port, or a dedicated charger.
VBUS_detect This interrupt pin connected to the USB VBUS signal detects when the device has been
plugged into or unplugged from the USB bus. If the system requires waking up from a low
power mode on being plugged into the USB port, this interrupt should also be a low power
wake up source. If this pin multiplexes other functions, such as GPIO, the pin can be
configured as an interrupt so that the USB plug or unplug event can be detected.
1. If the USB host has suspended the USB device, system software must configure the system to limit the current drawn from
the USB bus to 2.5 mA or less.
41.5.1 The charger detection sequence
The following figure illustrates the charger detection sequence in a simplified timing
diagram based on the USB Battery Charging Specification v1.1.
Functional description
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
938 Freescale Semiconductor, Inc.