Datasheet

PIC24FJ256GB210 FAMILY
DS39975A-page 236  2010 Microchip Technology Inc.
FIGURE 18-5: DUAL POWER EXAMPLE
18.1.2 HOST AND OTG MODES
18.1.2.1 D+ and D- Pull-Down Resistors
PIC24FJ256GB210 family devices have a built-in
15 k pull-down resistor on the D+ and D- lines. These
are used in tandem to signal to the bus that the micro-
controller is operating in Host mode. They are engaged
by setting the HOSTEN bit (U1CON<3>). If the OTGEN
bit (U1OTGCON<2>) is set, then these pull-downs are
enabled by setting the DPPULDWN and DMPULDWN
bits (U1OTGCON<5:4>).
18.1.2.2 Power Configurations
In Host mode, as well as Host mode in On-The-Go
operation, the “USB 2.0 OTG Specification” requires
that the host application should supply power on VBUS.
Since the microcontroller is running below V
BUS, and is
not able to source sufficient current, a separate power
supply must be provided.
When the application is always operating in Host mode,
a simple circuit can be used to supply V
BUS and
regulate current on the bus (Figure 18-6). For OTG
operation, it is necessary to be able to turn VBUS on or
off as needed, as the microcontroller switches between
Device and Host modes. A typical example using an
external charge pump is shown in Figure 18-7.
FIGURE 18-6: HOST INTERFACE EXAMPLE
VDD
VUSB
VBUS
VSS
Attach Sense
V
BUS
VSELF
100
~3.3V
~5V
100 k
3.3V
Low I
Q
Regulator
A/D Pin
VUSB
VDD
VSS
D+
D-
V
BUS
ID
D+
D-
V
BUS
ID
GND
+3.3V
+3.3V
Polymer PTC
Thermal Fuse
Micro A/B
Connector
150 µF
2 k
2 k
0.1 µF,
3.3V
+5V
PIC
®
MCU