11 EZ-USB Power Management
11.1 Introduction
The USB host can suspend a device to put it into a power-down mode. When the USB
signals a SUSPEND operation, the EZ-USB chip goes through a sequence of steps to
allow the 8051 to first turn off external power-consuming subsystems, and then enter an
ultra-low-power mode by turning off its oscillator. Once suspended, the EZ-USB chip is
awakened either by resumption of USB bus activity, or by assertion of its WAKEUP# pin.
This chapter describes the suspend-resume mechanism.
12 MHz
WAKEUP pin
START
USB Resume
Oscillator
STOP
PLL
48 MHz
Restart
Delay
div by
2
CLK24
PCON.0
Signal
Resume
Resume INT
8051
(USBCS.0)
USB
"SUSPEND"
Interrupt
No USB activity
for 3 msec.
Figure 11-1. Suspend-Resume Control
Figure 11-1 illustrates the EZ-USB logic that implements USB suspend and resume.
These operations are explained in the next sections.
EZ-USB TRM v1.9
Chapter 11. EZ-USB Power Management
Page 11-1
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