PIC18F-LF1XK50 MICROCHIP [Microchip Technology], PIC18F-LF1XK50 Datasheet - Page 271

• Manufacturer Part Number: PIC18F-LF1XK50
• Description: 20-Pin USB Flash Microcontrollers
• Manufacturer: MICROCHIP [Microchip Technology]

22.6
Many USB applications will likely have several different
sets of power requirements and configuration. The
most common power modes encountered are Bus
Power Only, Self-Power Only and Dual Power with
Self-Power Dominance. The most common cases are
presented here. Also provided is a means of estimating
the current consumption of the USB transceiver.
22.6.1
In Bus Power Only mode, all power for the application
is drawn from the USB
the simplest power method for the device.
In order to meet the inrush current requirements of the
USB 2.0 specifications, the total effective capacitance
appearing across V
than 10 µF. If not, some kind of inrush liming is
required. For more details, see section 7.2.4 of the
USB 2.0 specification.
According to the USB 2.0 specification, all USB devices
must also support a Low-Power Suspend mode. In the
USB Suspend mode, devices must consume no more
than 500 A (or 2.5 mA for high powered devices that
are remote wake-up capable) from the 5V V
the USB cable.
The host signals the USB device to enter the Suspend
mode by stopping all USB traffic to that device for more
than 3 ms. This condition will cause the IDLEIF bit in
the UIR register to become set.
During the USB Suspend mode, the D+ or D- pull-up
resistor must remain active, which will consume some
of the allowed suspend current: 500 A/2.5 mA budget.
FIGURE 22-9:
 2010 Microchip Technology Inc.
V
BUS
USB Power Modes
BUS POWER ONLY
BUS
BUS POWER ONLY
(Figure
and ground must be no more
22-9). This is effectively
V
V
V
DD
USB
SS
BUS
line of
Preliminary
22.6.2
In Self-Power Only mode, the USB application provides
its own power, with very little power being pulled from
the USB.
In order to meet compliance specifications, the USB
module (and the D+ or D- pull-up resistor) should not
be enabled until the host actively drives V
The application should never source any current onto
the 5V V
FIGURE 22-10:
BUS
V
Figure 22-10
PIC18F/LF1XK50
SELF
SELF-POWER ONLY
pin of the USB cable.
SELF-POWER ONLY
shows an example.
DS41350E-page 271
V
V
V
BUS
USB
DD
SS
high.