PIC24FJ256GB110-I Datasheet, PDF (202/328 Pages) Microchip Technology – 64/80/100-Pin, 16-Bit Flash Microcontrollers with USB On-The-Go (OTG)

PIC24FJ256GB110 FAMILY
17.2 VBUS Voltage Generation
When operating as a USB host, either as an A-device
in an OTG configuration or as an embedded host, VBUS
must be supplied to the attached device.
PIC24FJ256GB110 family devices have an internal
VBUS boost assist to help generate the required 5V
VBUS from the available voltages on the board.
Figure 17-3 shows how the internal VBUS components
of the USB OTG module work in A-device and B-device
configurations.
To enable voltage generation:
1. Verify that the USB module is powered
(U1PWRC<0> = 1) and that the VBUS discharge
is disabled (U1OTGCON<0> = 0).
2. Set the PWM period (U1PWMRRS<7:0>) and
duty cycle (U1PWMRRS<15:8>) as required.
3. Select the required polarity of the output signal
based on the configuration of the external circuit
with the PWMPOL bit (U1PWMCON<9>).
4. Select the desired target voltage using the
VBUSCHG bit (U1OTGCON<1>).
5. Enable the PWM counter by setting the CNTEN
bit to ‘1’ (U1PWMCON<8>).
6. Enable the PWM module by setting the PWMEN
bit to ‘1’ (U1PWMCON<15>).
7. Enable the VBUS generation circuit
(U1OTGCON<3> = 1).
Note:
This section describes the general
process for VBUS voltage generation and
control. Please refer to the “PIC24F
Family Reference Manual” for additional
examples.
FIGURE 17-3:
USB VOLTAGE GENERATION AND CONNECTIONS BETWEEN AN A-DEVICE
AND A B-DEVICE
USB
SIE
PIC24FJ256GB1XX
A-DEVICE (HOST)
5V BOOST
ASSIST⁽¹⁾
PIC24FJ256GB1XX
B-DEVICE
5V BOOST
ASSIST
USB
SIE
VBUS
COMPARATORS
3.3V
REGULATOR
VBUS (5V)
D+
D-
GND
ID
VBUS
COMPARATORS
3.3V
REGULATOR
GND
ID
D+
XCVR
D-
D+
D-
XCVR
GND
ID
Note 1: Additional external components (not shown here) and software configuration are required for a host device to generate
VBUS. For more information, refer to the “PIC24F Family Reference Manual”.
DS39897B-page 200
Preliminary
© 2008 Microchip Technology Inc.