NXP Semiconductors freescale K51 Series Reference Manual

Table 44-13. USB Battery Charger Subsystem ComponentsComponent DescriptionBattery Charger IC The external battery charger IC regulates the charge rate to the rechargable battery. Systemsoftware is responsible for communicating the appropriate charge rates.Charger Maximum Current Drawn1Standard host port up to 500 mACharging host port up to 1500 mADedicated charging port up to 1800 mA1. If the USB host has suspended the USB device, system software must configure thesystem to limit the current drawn from the USB bus to 2.5 mA or less.Comm Module A communications module on the device can be used to control the charge rate of the batterycharger IC.System software Coordinates the detection activities of the subsystem.USB Controller The D+ pullup enable control signal plays a role during the charger type detection phase.System software must issue a command to the USB controller to assert this signal. Once thispullup is enabled, the device is considered to be connected to the USB bus. The host thenattempts to enumerate it.Note that the USB controller must be used only for USB device applications when using theUSBDCD module. For USB host applications the USBDCD module must be disabled.USB Transceiver The USB transceiver contains the pullup resistor for the USB D+ signal and the pulldownresistors for the USB D+ and D- signals. The D+ pullup and the D- pulldown are both usedduring the charger detection sequence. The USB transceiver also outputs the digital state ofthe D+ and D- signals from the USB bus.The pullup and pulldown enable signals are controlled by other modules during the chargerdetection sequence: The D+ pullup enable is physically output from the USB controller but isunder software control. The USBDCD module controls the D- pulldown enable.USBDCD Module Detects if 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 beenplugged into or unplugged from the USB bus. If the system requires waking up from a lowpower mode upon being plugged into the USB port, this interrupt should also be a low powerwake up source. If this pin multiplexes other functions, such as GPIO, the pin should beconfigured as an interrupt whenever the USB plug or unplug event is required to be detected.1. If the USB host has suspended the USB device, system software must configure the system to limit the current drawn fromthe USB bus to 2.5 mA or less.44.5.1 The Charger Detection SequenceThe following figure illustrates the charger detection sequence in a simplified timingdiagram based on the USB Battery Charging Specification v1.1.Chapter 44 USB Device Charger Detection Module (USBDCD)K51 Sub-Family Reference Manual, Rev. 6, Nov 2011Freescale Semiconductor, Inc. 1105