Texas Instruments MSP-EXP430F5529LP 사용자 설명서
Hardware
USB hosts supply a 5-V power rail to USB devices, called "VBUS". This is convenient for USB devices; if
they only need to function while attached to a host (for example, mice or keyboards) then they may not
need their own power source. Even if they need to function apart from the USB host and, thus, need their
own power source, being attached to the host places power demands on that device which may not be
present when the device is not attached; the availability of VBUS can help offset these demands.
they only need to function while attached to a host (for example, mice or keyboards) then they may not
need their own power source. Even if they need to function apart from the USB host and, thus, need their
own power source, being attached to the host places power demands on that device which may not be
present when the device is not attached; the availability of VBUS can help offset these demands.
The F5529 LaunchPad has a high-efficiency dc-dc converter, a
, that derives a new power rail
of 3.3 V from VBUS. This 3.3-V rail sources the eZ-FET lite, hub, target F5529 device, and the 3.3-V pin
on the BoosterPack header.
on the BoosterPack header.
VBUS is still made available to the target F5529 device for two reasons. One reason is that the presence
of VBUS is how a USB device determines the presence of a USB host. The other reason is that VBUS
also supplies power to the target F5529's USB module.
of VBUS is how a USB device determines the presence of a USB host. The other reason is that VBUS
also supplies power to the target F5529's USB module.
Note that USB-equipped MSP430's have an integrated 5-V to 3.3-V LDO. On the F5529 LaunchPad, this
LDO is only used for the MSP430F5529 USB operation. However, the integrated LDO also has an output
pin that can source a modest amount of power to external circuitry. See the device data sheet for more
details. Sometimes, this output pin can eliminate the need for external power management. But because
the current limit may be too low for some applications, the F5529 LaunchPad uses the external dc-dc
converter.
LDO is only used for the MSP430F5529 USB operation. However, the integrated LDO also has an output
pin that can source a modest amount of power to external circuitry. See the device data sheet for more
details. Sometimes, this output pin can eliminate the need for external power management. But because
the current limit may be too low for some applications, the F5529 LaunchPad uses the external dc-dc
converter.
If desired, 3.3 V can be supplied from an external source to the power header pin. But to do this, the 3.3-V
jumper on the isolation jumper block must be disconnected. See
jumper on the isolation jumper block must be disconnected. See
for more information.
2.2.5
Clocking
The F5529 LaunchPad provides two resonators on the target F5529:
•
XT1: a 32-kHz crystal
•
XT2: a 4-MHz ceramic resonator, within ±2500-ppm precision
The 32-kHz crystal allows for lower LPM3 sleep currents than do the other low-frequency clock sources.
Therefore, the presence of the crystal allows the full range of low-power modes to be used.
Therefore, the presence of the crystal allows the full range of low-power modes to be used.
USB operation on the MSP430F5529 requires a high-frequency reference clock for the USB PLL. To meet
this need, the F5529 LaunchPad has a 4-MHz ceramic resonator on the XT2 oscillator. This particular
ceramic resonator operates within ±2500 ppm, which is important for USB operation. If the F5529
application needs a high-frequency precision clock for purposes other than USB, then this clock is
available for this as well.
this need, the F5529 LaunchPad has a 4-MHz ceramic resonator on the XT2 oscillator. This particular
ceramic resonator operates within ±2500 ppm, which is important for USB operation. If the F5529
application needs a high-frequency precision clock for purposes other than USB, then this clock is
available for this as well.
For information on how clocks are configured by the software examples, see
.
2.2.6
Application (or "Backchannel") UART
The backchannel UART allows communication with the USB host that is not part of the target application's
main functionality. This is very useful during development. For example, if, while developing a USB
interface, you want to send debug information to the host without using the USB interfaces under
development to do so.
main functionality. This is very useful during development. For example, if, while developing a USB
interface, you want to send debug information to the host without using the USB interfaces under
development to do so.
shows the pathway of the backchannel UART. The backchannel UART (USCI_A1) is
independent of the UART on the 40-pin BoosterPack connector (USCI_A0).
17
SLAU533A – September 2013 – Revised January 2014
MSP430F5529 LaunchPad™ Development Tool (MSP
‑
EXP430F5529LP)
Copyright © 2013–2014, Texas Instruments Incorporated