Information

41.5 Functional description
The sequence of detecting the presence of charging port and type of charging port
involves several hardware components, coordinated by system software. This collection
of interacting hardware and software is called the USB Battery Charging Subsystem. The
following figure shows the USBDCD module as a component of the subsystem. The
following table describes the components.
USBDCD
Module
Control
and Status
System
Software
Device
Control
Battery
Charger
IC
System Interrupt
Connector
USB Transceiver
Pullup Enable
Command
Charge
Rate
Comm
VBUS_detect
Pulldown
Enable
D
USB
Controller
USB
Bus
D
VBUS
Standard
Host Port
Dedicated
Charger
or
or
Charging
Host Port
D
D
Pullup
Enable
Module
Figure 41-8. USB battery charging subsystem
Table 41-13. USB battery charger subsystem components
Component Description
Battery Charger IC The external battery charger IC regulates the charge rate to the rechargable battery. System
software is responsible for communicating the appropriate charge rates.
Charger Maximum current drawn
1
Standard host port up to 500 mA
Charging host port up to 1500 mA
Dedicated charging port up to 1800 mA
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.
Comm Module
A communications module on the device can be used to control the charge rate of the battery
charger 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. After this
pullup is enabled, the device is considered to be connected to the USB bus. The host then
attempts to enumerate it.
NOTE: The USB controller must be used only for USB device applications when using the
USBDCD module. For USB host applications, the USBDCD module must be
disabled.
Table continues on the next page...
Chapter 41 USB Device Charger Detection Module (USBDCD)
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
Freescale Semiconductor, Inc. 937