PIC16LF1454 Datasheet, PDF (320/418 Pages) Microchip Technology – 14/20-Pin Flash, 8-Bit USB Microcontrollers with XLP Technology

PIC16(L)F1454/5/9
26.6 USB Power Modes
The USB peripheral often has different power
requirements and configurations depending on the
application.
The most common cases are presented here:
• Bus Power Only
• Self-Power Only
• Dual Power with Self-Power Dominance
Means of estimating the current consumption of the
USB transceiver are also provided.
26.6.1 BUS POWER ONLY
In Bus Power Only mode, all power for the application
is drawn from the USB (Figure 26-8). This is effectively
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 VBUS and ground must be no more
than 10 F. Circuitry is required to limit inrush current,
see section 7.2.4 of the USB specification for more
detail.
All USB devices must support a Low-Power Suspend
mode which meets the current limits from the 5V VBUS
line of the USB cable according to the USB 2.0 specifi-
cation. For high-powered devices that are remote
wake-up capable, a higher limit is allocated. Refer to
USB Specification 2.0, 7.2.3 for information.
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 budget.
FIGURE 26-8:
BUS POWER ONLY
VBUS
VDD
VUSB3V3
VSS
In order to meet compliance specifications, the USB
module (and the D+ or D- internal pull-ups) should not
be enabled until the host actively drives VBUS high.
The application should never source any current onto
the 5V VBUS pin of the USB cable.
FIGURE 26-9:
SELF-POWER ONLY
VSELF
VDD
VUSB3V3
VSS
26.6.3 DUAL POWER WITH SELF-POWER
DOMINANCE
In Dual Power with Self-Power Dominance mode, the
application uses internal power as the primary source,
but can switch power from the USB when no internal
power is available. Figure 26-10 shows a 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 (or the
D+/D- internal pull-ups) until VBUS is driven high. See
Section 26.6.1 “Bus Power Only” and
Section 26.6.2 “Self-Power Only” for descriptions of
those requirements. Additionally, dual power devices
must never source current onto the 5V VBUS pin of the
USB cable.
FIGURE 26-10: DUAL POWER EXAMPLE
VBUS
~5V
100 k
VSELF
~5V
VDD
VUSB3V3
VSS
26.6.2 SELF-POWER ONLY
In Self-Power Only mode, the USB application provides
its own power, with very little power being pulled from
the USB. Figure 26-9 shows an example.
Note:
Users should keep in mind the limits for
devices drawing power from the USB.
Refer to USB Specification 2.0, 7.2.3 for
more information.
DS41639A-page 320
Preliminary
 2012 Microchip Technology Inc.