PIC24FJ128GC010 Datasheet, PDF (267/472 Pages) Microchip Technology – 16-Bit Flash Microcontrollers with 12-Bit Pipeline A/D, Sigma-Delta A/D, USB On-The-Go and XLP Technology

PIC24FJ128GC010 FAMILY
19.1 Hardware Configuration
19.1.1 DEVICE MODE
19.1.1.1 D+ Pull-up Resistor
PIC24FJ128GC010 family devices have a built-in
1.5 k resistor on the D+ line that is available when the
microcontroller is operating in Device mode. This is
used to signal an external host that the device is
operating in Full-Speed Device mode. It is engaged by
setting the USBEN bit (U1CON<0>) and powering up
the USB module (USBPWR = 1). If the OTGEN bit
(U1OTGCON<2>) is set, then the D+ pull-up is enabled
through the DPPULUP bit (U1OTGCON<7>).
19.1.1.2 The VBUS Pin
In order to meet the USB 2.0 specification requirement,
relating to the back drive voltage on the D+/D- pins, the
USB module incorporates VBUS level sensing compar-
ators. When the comparators detect the VBUS level
below the VA_SESS_VLD level, the hardware will auto-
matically disable the D+ pull-up resistor described in
Section 19.1.1.1 “D+ Pull-up Resistor”. This allows
the device to automatically meet the back drive require-
ment for D+ and D-, even if the application firmware
does not explicitly monitor the VBUS level. Therefore,
the VBUS microcontroller pin should not be left floating
in USB Device mode application designs, and should
normally be connected to the VBUS pin on the USB
connector/cable (either directly or through a small
resistance  100 ohms).
19.1.1.3 Power Modes
Many USB applications will likely have several different
sets of power requirements and configuration. The
most common power modes encountered are:
• Bus Power Only mode
• Self-Power Only mode
• Dual Power with Self-Power Dominance
Bus Power Only mode (Figure 19-2) is effectively the
simplest method. All power for the application is drawn
from the USB.
To meet the inrush current requirements of the
“USB 2.0 OTG Specification”, the total effective capac-
itance, appearing across VBUS and ground, must be no
more than 10 F.
In the USB Suspend mode, devices must consume no
more than 2.5 mA from the 5V VBUS line of the USB
cable. During the USB Suspend mode, the D+ or D-
pull-up resistor must remain active, which will consume
some of the allowed suspend current.
In Self-Power Only mode (Figure 19-3), the USB
application provides its own power, with very little
power being pulled from the USB. Note that an attach
indication is added to indicate when the USB has been
connected and the host is actively powering VBUS.
To meet compliance specifications, the USB module
(and the D+ or D- pull-up resistor) should not be enabled
until the host actively drives VBUS high. One of the 5.5V
tolerant I/O pins may be used for this purpose.
The application should never source any current onto
the 5V VBUS pin of the USB cable when the USB
module is operated in USB Device mode.
The Dual Power mode with Self-Power Dominance
(Figure 19-4) allows the application to use internal
power primarily, but switch to power from the USB
when no internal power is available. Dual power
devices must also meet all of the special requirements
for inrush current and Suspend mode current previ-
ously described, and must not enable the USB module
until VBUS is driven high.
FIGURE 19-2:
BUS-POWERED
INTERFACE EXAMPLE
VBUS
~5V
100
Attach Sense _VBUS
3.3V
VDD
MCP1801
3.3V LDO
1 F
VUSB3V3
VSS
FIGURE 19-3:
SELF-POWER ONLY
VBUS
~5V
VSELF
~3.3V
100
Attach Sense
VBUS
VDD
100 k
VUSB3V3
VSS
FIGURE 19-4:
DUAL POWER EXAMPLE
100
VBUS
~5V
3.3V
Low IQ
Regulator
VSELF
~3.3V
100 k
Attach Sense _VBUS
VDD
VUSB3V3
VSS
 2012-2013 Microchip Technology Inc.
DS30009312B-page 267