Microchip Technology MA180021 User Manual
Hardware Configuration/Jumper Settings
© 2007 Microchip Technology Inc.
DS51678A-page 13
3.4
LINEAR REGULATOR/POWER MANAGEMENT
The USB interface provides +5V (nominal) at up to 500 mA (only 100 mA can be
ensured) for use by USB peripheral devices. In order to take advantage of this bus
provided power, a 3.3V low drop out, low quiescent current linear regulator
(TC1108-3.3VDB) has been included on the PIM. This enables the PIM to be purely bus
powered, providing power to both the PIM and the HPC Explorer board if connected.
Alternatively, when used in conjunction with the HPC Explorer, the PIM may obtain
power from the HPC board. When a suitable power source is connected to power jack,
J1 on the HPC Explorer board, the board will natively produce a regulated 5V provided
by the on-board adjustable linear regulator. When a PIM requiring 3.3V (such as the
PIC18F87J50 FS USB PIM) is plugged in, resistor, R2, located on the PIM alters the
feedback circuit of the adjustable linear regulator and configures it to produce 3.3V.
Therefore, no soldering or other modification is required to either the HPC Explorer or
the PIC18F87J50 FS USB PIM when they are used together.
Jumper, JP4, on the PIM serves two main purposes. JP4 is located in series with the
+5V V
ensured) for use by USB peripheral devices. In order to take advantage of this bus
provided power, a 3.3V low drop out, low quiescent current linear regulator
(TC1108-3.3VDB) has been included on the PIM. This enables the PIM to be purely bus
powered, providing power to both the PIM and the HPC Explorer board if connected.
Alternatively, when used in conjunction with the HPC Explorer, the PIM may obtain
power from the HPC board. When a suitable power source is connected to power jack,
J1 on the HPC Explorer board, the board will natively produce a regulated 5V provided
by the on-board adjustable linear regulator. When a PIM requiring 3.3V (such as the
PIC18F87J50 FS USB PIM) is plugged in, resistor, R2, located on the PIM alters the
feedback circuit of the adjustable linear regulator and configures it to produce 3.3V.
Therefore, no soldering or other modification is required to either the HPC Explorer or
the PIC18F87J50 FS USB PIM when they are used together.
Jumper, JP4, on the PIM serves two main purposes. JP4 is located in series with the
+5V V
BUS
supply from the USB cable to the rest of the PIM board (see Figure A-1 for
exact electrical location). In this location, the jumper cap can be removed, and a digital
current meter can be inserted across the posts of the header. This can be quite useful
during development, as it offers a means of determining how much current the applica-
tion (both the PIM and the HPC Explorer board if connected) is actively consuming from
the USB port. This is especially important when developing bus powered USB
applications that are intended to be fully USB compliant.
All USB devices are supposed to implement a low-power USB Suspend mode. The
host PC may, at its own discretion, halt all USB traffic (including Start-of-Frame
packets) to your device for more than 3 ms. Upon detecting this condition, the USB
peripheral device should drop to a low-power suspend state, whereby it draws no more
than 500
current meter can be inserted across the posts of the header. This can be quite useful
during development, as it offers a means of determining how much current the applica-
tion (both the PIM and the HPC Explorer board if connected) is actively consuming from
the USB port. This is especially important when developing bus powered USB
applications that are intended to be fully USB compliant.
All USB devices are supposed to implement a low-power USB Suspend mode. The
host PC may, at its own discretion, halt all USB traffic (including Start-of-Frame
packets) to your device for more than 3 ms. Upon detecting this condition, the USB
peripheral device should drop to a low-power suspend state, whereby it draws no more
than 500
μA (or in some cases, 2.5 mA; see the USB 2.0 specifications section 7.2.3)
from the +5V V
BUS
supply. Two USB interrupts, UIR<IDLEIF> and UIR<ACTVIF>, are
useful for detecting when the low-power suspend condition is supposed to begin and
when it ends. The TC1108-3.3VDB linear regulator was chosen for its low dropout, low
quiescent current consumption and good transient response capability.
when it ends. The TC1108-3.3VDB linear regulator was chosen for its low dropout, low
quiescent current consumption and good transient response capability.