All XMEGA Sleep modes are described in the XMEGA data sheet chapter
Power Management and Sleep Modes. The Sleep modes supported by the USB stack
are:
- USB IDLE state: the driver requires the
USB clock; hence IDLE Sleep mode is the lowest supported Sleep mode.
- USB SUSPEND state: the driver does not
require the USB clock, but will request the clock on USB wake-up. Hence, POWER DOWN and
STANDBY is supported.
Table 1. Sleep Modes Supported in USB SUSPEND
State on XMEGA| USB Power Mode |
USB Speed Mode |
USB Clock Start-up
(1) |
Sleep
Mode Authorized |
|---|
| Bus and
self-powered |
LS, FS |
>10ms |
STANDBY |
| Bus and
self-powered |
LS, FS |
<=10ms |
POWER
DOWN |
Note: (1)The internal oscillator can
be used to generate the USB clock. Hence, USB clock start-up timing is < 10ms.
The XMEGA family support the specified power limit (2.5mA) in USB Suspend
mode.
For any bus power device application, it is required to:
- Remove USB_CONFIG_ATTR_SELF_POWERED bit
in USB_DEVICE_ATTR define from conf_usb.h file.
- Use the internal oscillator to reduce
the start-up time.
- Use an external Low Dropout (LDO)
voltage regulator, or similar, to generate 3.3V for the XMEGA. When selecting this
regulator, be sure its quiescent current does not consume a too large of a proportion of
the required 2.5mA maximum suspend current.