PIC24FJ128GC010 Datasheet, PDF (269/472 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
19.1.3 USING AN EXTERNAL INTERFACE
Some applications may require the USB interface to
be isolated from the rest of the system.
PIC24FJ128GC010 family devices include a complete
interface to communicate with and control an external
USB transceiver, including the control of data line
pull-ups and pull-downs. The VBUS voltage generation
control circuit can also be configured for different VBUS
generation topologies.
Refer to the “PIC24F Family Reference Manual”,
Section 27. “USB On-The-Go (OTG)” for information
on using the external interface.
19.1.4
CALCULATING TRANSCEIVER
POWER REQUIREMENTS
The USB transceiver consumes a variable amount of
current depending on the characteristic impedance of
the USB cable, the length of the cable, the VUSB supply
voltage and the actual data patterns moving across the
USB cable. Longer cables have larger capacitances
and consume more total energy when switching output
states. The total transceiver current consumption will
be application-specific. Equation 19-1 can help
estimate how much current actually may be required in
full-speed applications.
Refer to the “PIC24F Family Reference Manual”,
Section 27. “USB On-The-Go (OTG)” for a complete
discussion on transceiver power consumption.
EQUATION 19-1: ESTIMATING USB TRANSCEIVER CURRENT CONSUMPTION
IXCVR = ^{40 mA • VUSB • PZERO • PIN • LCABLE} + IPULLUP
3.3V • 5m
Legend: VUSB – Voltage applied to the VUSB3V3 pin in volts (3.0V to 3.6V).
PZERO – Percentage (in decimal) of the IN traffic bits sent by the PIC^® microcontroller that are a value
of ‘0’.
PIN – Percentage (in decimal) of total bus bandwidth that is used for IN traffic.
LCABLE – Length (in meters) of the USB cable. The “USB 2.0 OTG Specification” requires that
full-speed applications use cables no longer than 5m.
IPULLUP – Current which the nominal, 1.5 k pull-up resistor (when enabled) must supply to the USB
cable.
 2012-2013 Microchip Technology Inc.
DS30009312B-page 269