PIC18F25J50 MICROCHIP [Microchip Technology], PIC18F25J50 Datasheet - Page 378

• Manufacturer Part Number: PIC18F25J50
• Description: 28/44-Pin, Low-Power, High-Performance USB Microcontrollers with nanoWatt XLP Technology
• Manufacturer: MICROCHIP [Microchip Technology]

PIC18F46J50 FAMILY
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 Specification”, the total effective capacitance
appearing across V
than 10 µF. If not, some kind of inrush timing 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 2.5 mA from the 5V V
of 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: 2.5 mA budget.
FIGURE 22-9:
22.6.2
In Self-Power Only mode, the USB application provides
its own power, with very little power being pulled from
the USB. See
Note that an attach indication is added to indicate when
the USB has been connected and the host is actively
powering V
DS39931D-page 378
V
USB Power Modes
~5V
BUS
BUS
Low I
BUS POWER ONLY
SELF-POWER ONLY
Figure 22-10
.
Q
Regulator
BUS
BUS POWER ONLY
(Figure
and ground must be no more
3.3V
for an example.
22-9). This is effectively
V
V
V
DD
USB
SS
BUS
line
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 5.5V tolerant I/O pins may be used for this purpose.
The application should never source any current onto
the 5V V
FIGURE 22-10:
22.6.3
Some applications may require a dual power option.
This allows the application to use internal power
primarily, but switch to power from the USB when no
internal power is available. See
simple Dual Power with Self-Power Dominance mode
example, which automatically switches between
Self-Power Only and USB Bus Power Only modes.
Dual power devices must also meet all of the special
requirements for inrush current and Suspend mode
current, and must not enable the USB module until
V
Only”
descriptions of those requirements. Additionally, dual
power devices must never source current onto the 5V
V
FIGURE 22-11:
V
BUS
BUS
V
~3.3V
~5V
Note:
BUS
V
SELF
~5V
BUS
Regulator
pin of the USB cable.
is driven high. See
Low I
100 k
and
BUS
V
~3.3V
100 k
SELF
DUAL POWER WITH SELF-POWER
DOMINANCE
Q
Users should keep in mind the limits for
devices drawing power from the USB.
According to “USB Specification 2.0”, this
cannot exceed 100 mA per low-power
device or 500 mA per high-power device.
pin of the USB cable.
Section 22.6.2 “Self-Power Only”
3.3V
100 k
SELF-POWER ONLY
DUAL POWER EXAMPLE
 2011 Microchip Technology Inc.
Section 22.6.1 “Bus Power
Attach Sense
Attach Sense
100 k
Figure 22-11
BUS
5.5V Tolerant
I/O Pin
V
V
V
DD
USB
SS
high. One of
I/O pin
V
V
V
DD
USB
SS
for a
for