U.S. patent application number 13/765464 was filed with the patent office on 2013-06-20 for universal serial bus current limit.
This patent application is currently assigned to RESEARCH IN MOTION LIMITED. The applicant listed for this patent is RESEARCH IN MOTION LIMITED. Invention is credited to Marc A. Drader, David James Mak-Fan, Dusan Veselic.
Application Number | 20130159737 13/765464 |
Document ID | / |
Family ID | 35446893 |
Filed Date | 2013-06-20 |
United States Patent
Application |
20130159737 |
Kind Code |
A1 |
Drader; Marc A. ; et
al. |
June 20, 2013 |
Universal Serial Bus Current Limit
Abstract
A load device includes a power input having an interface to a
power supply; a peripheral power bus including an internal
capacitance, and an active switch coupled to the power input and
the peripheral power bus for applying power from the power input to
the peripheral power bus. The load device also includes a switch
controller coupled to the active switch for regulating the in-rush
current drawn by the internal capacitance through the active switch
while the internal capacitance is being charged.
Inventors: |
Drader; Marc A.; (Lans en
Vercors, FR) ; Mak-Fan; David James; (Waterloo,
CA) ; Veselic; Dusan; (Oakville, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
RESEARCH IN MOTION LIMITED; |
Waterloo |
|
CA |
|
|
Assignee: |
RESEARCH IN MOTION LIMITED
Waterloo
ON
|
Family ID: |
35446893 |
Appl. No.: |
13/765464 |
Filed: |
February 12, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10857966 |
Jun 2, 2004 |
8378527 |
|
|
13765464 |
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Current U.S.
Class: |
713/300 ;
307/109 |
Current CPC
Class: |
G06F 1/26 20130101; G05F
3/08 20130101 |
Class at
Publication: |
713/300 ;
307/109 |
International
Class: |
G05F 3/08 20060101
G05F003/08; G06F 1/26 20060101 G06F001/26 |
Claims
1. A load device, comprising: a system power bus having a universal
serial bus (USB) interface; a peripheral power bus; an active
switch coupled to the system power bus and the peripheral power bus
for applying power from the system power bus to the peripheral
power bus and for controlling a plurality of operation intervals of
the active switch; and a switch controller coupled to the active
switch, the switch controller cyclically opening and closing the
active switch by applying a periodic gate signal during a first
operational interval of the plurality of operational intervals, the
periodic gate signal comprising a plurality of pulses, so as to
limit the current drawn by the peripheral power bus to be within
USB standard limits, and the switch controller maintaining the
active switch fully on during a second operational interval of the
plurality of operational intervals.
2. The load device of claim 1, wherein the second operational
interval begins when one or more capacitors in communication with
the peripheral power bus have charged up to a predetermined voltage
level.
3. The load device of claim 1, wherein the applied periodic gate
signal is further determined to maintain an instantaneous voltage
at the system bus above a predetermined lower limit.
4. The load device of claim 1, wherein the applied periodic gate
signal is further determined to bring at least one capacitor in
communication with the peripheral power bus up to a predetermined
voltage level.
5. The load device of claim 3, wherein the pulse-width is
predetermined to maintain the instantaneous voltage at the system
bus above the predetermined lower limit.
6. The load device of claim 1, wherein the load comprises a
portable computing device.
7. The load device of claim 1, wherein the instantaneous voltage at
the system power bus is maintained below an instantaneous voltage
of the peripheral power bus.
8. In a load comprising a system power bus having a universal
serial bus (USB) interface, a peripheral power bus, and an active
switch for applying power from the system power bus to the
peripheral power bus and for controlling a plurality of operational
intervals of the active switch, a method comprising: applying a
periodic gate signal to the active switch input, the periodic gate
signal determined to cyclically open and close the active switch
during a first operational interval of the plurality of operational
intervals, the periodic gate signal comprising a plurality of
pulses, so as to limit the current drawn to be within USB standard
limits, and maintaining the active switch fully on during a second
operational interval of the plurality of intervals.
9. The method of claim 8, wherein the second operational interval
begins when one or more capacitors in communication with the
peripheral power bus have charged up to a predetermined voltage
level.
10. The method of claim 8, wherein the applied periodic gate signal
is further determined to maintain an instantaneous voltage at the
system bus above a predetermined lower limit.
11. The method of claim 8, further comprising determining the
applied gate signal such that one or more capacitors in
communication with the peripheral power bus are charged up to a
predetermined voltage level.
12. The method of claim 10, wherein a pulse-width of the plurality
of pulses is predetermined to maintain the instantaneous voltage at
the system bus above the predetermined lower limit.
13. The method of claim 8, wherein the load comprises a portable
computing device.
14. A computer-readable medium including computer processing
instructions for a processing unit of a portable computing device,
the portable computing device comprising a system power bus having
a universal serial bus (USB) interface, a peripheral power bus, and
an active switch coupled to the system power bus and the peripheral
power bus for applying power from the system power bus to the
peripheral power bus and for controlling a plurality of operational
intervals of the active switch, the computer processing
instructions when executed by the processing unit causing the
portable computing device to: cyclically open and close the active
switch during a first operational interval of the plurality of
intervals by applying a periodic gate signal , the periodic gate
signal comprising a plurality of pulses, all of the pulses having
substantially identical pulse-width, to limit the current drawn by
the peripheral power bus to be within USB standard limits, and
maintain the active switch fully on during a second operational
interval of the plurality of operational intervals.
15. The computer-readable medium of claim 14, wherein the second
operational interval begins when one or more capacitors in
communication with the peripheral power bus have charged up to a
predetermined voltage level.
16. The computer-readable medium of claim 14, wherein the applied
periodic gate signal is further determined to maintain an
instantaneous voltage at the system bus above a predetermined lower
limit.
17. The computer-readable medium of claim 16, wherein the
pulse-width is predetermined to maintain the instantaneous voltage
at the system bus above the predetermined lower limit.
18. The computer-readable medium of claim 14, wherein the computer
processing instructions further cause the portable computing device
to cyclically open and close the active switch with the periodic
gate signal until the one or more capacitors have charged up to a
predetermined voltage level.
19. The computer-readable medium of claim 14, wherein the
instantaneous voltage at the system power bus is maintained below
an instantaneous voltage of the peripheral power bus.
Description
FIELD OF THE INVENTION
[0001] The invention described herein relates to a mechanism for
interfacing a load with a power supply. In particular, the
invention described herein relates to a method and apparatus for
powering a load from a current-limited power supply in
circumstances where the interim load current demands of the load
might exceed the current source capabilities of the power
supply.
BACKGROUND OF THE INVENTION
[0002] The Universal Serial Bus (USB) standard was an improvement
over the conventional serial bus standard, partly due to the fact
that the USB cable could supply power to the peripheral device. As
a result, peripheral manufacturers could supply new peripherals
which did not need there own respective power supply adapter.
[0003] The USB standard imposes a limit on the maximum allowable
current that a peripheral device can draw from the VBUS. According
to the USB standard, a device attached to the VBUS must limit its
current draw to 100 mA for low power bus-powered devices, and 500
mA for high power bus-powered devices. This limitation prevents
peripheral devices which have excessive load current demands from
damaging the USB connection.
[0004] A peripheral device might draw an excessive load current
("in-rush current") only for the interim period required to charge
the internal capacitors of the peripheral device. Thereafter, the
current drawn by the peripheral device might be within the maximum
allowable limit. However, the interim period may be greater than
that tolerated by the USB standard. As a result, the number of
peripheral devices that can take advantage of the power supply
capabilities of the USB standard is limited.
[0005] Therefore, there is a need for a mechanism for powering a
load from a current-limited power supply where the interim load
current demands of the load might exceed the current source
capabilities of the power supply. Moreover, there is a need for an
improved mechanism for powering a peripheral device having a large
in-rush current draw from a USB connection.
SUMMARY OF THE INVENTION
[0006] According to one aspect of the invention described herein,
there is provided a load device that includes a power input to a
power supply; a peripheral power bus having an internal
capacitance, and an active switch coupled to the power input and
the peripheral power bus for applying power from the power input to
the peripheral power bus. The load device also includes a switch
controller coupled to the active switch for regulating the in-rush
current drawn by the internal capacitance through the active
switch.
[0007] According to another aspect of the invention described
herein, in a load comprising a power input to a power supply, a
peripheral power bus including an internal capacitance, and an
active switch for applying power from the power input to the
peripheral power bus, a method for powering the load from the power
supply involves regulating an in-rush current drawn by the internal
capacitance through the active switch.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The invention will now be described, by way of example only,
with reference to the accompanying drawings, in which:
[0009] FIG. 1 is a front plan view of a handheld computing device,
according the invention described herein;
[0010] FIG. 2 is a schematic view depicting functional details of
the handheld computing device;
[0011] FIG. 3 is a schematic view of the circuitry comprising the
power management subsystem; and
[0012] FIG. 4 is a diagram of the charging waveform for the system
power bus and the peripheral power bus capacitors of the power
management subsystem.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0013] Referring now to FIG. 1, there is shown a handheld computing
device, denoted generally as 100, provided according to one aspect
of the invention. The handheld computing device 100 includes a
display 122, a function key 146 and a system motherboard (not
shown) disposed within a common housing. The display 122 is a
self-contained peripheral device that is connected to and receives
power from the system motherboard. In one the embodiment, the
display 122 comprises a reflective or trans-reflective LCD display.
Alternately, in another embodiment, the display 122 comprises a
transmissive LCD display. Although these types of displays 122 do
not draw significant power during normal operation, the in-rush
current drawn by these types of displays 122 when they are powered
up can be significant.
[0014] The function key 146 functions as a power on/off switch for
the handheld computing device 100, and may also function as a
backlight key for the display 122.
[0015] In addition to the display 122 and the function key 146, the
handheld computing device 100 includes user data input means for
inputting data to the data processing means. As shown, preferably
the user data input means includes a keyboard 132, a thumbwheel 148
and an escape key 160.
[0016] Typically, the handheld computing device 100 is a two-way
wireless communication device having at least voice and data
communication capabilities. Further, preferably the handheld
computing device 100 has the capability to communicate with other
computer systems on the Internet. Depending on the exact
functionality provided, the wireless handheld computing device 100
may be referred to as a data messaging device, a two-way pager, a
wireless e-mail device, a cellular telephone with data messaging
capabilities, a wireless Internet appliance, or a data
communication device, as examples.
[0017] FIG. 2 depicts functional details of the handheld computing
device 100. Where the handheld computing device 100 is enabled for
two-way communication, it will incorporate a communication
subsystem 111, including both a receiver 112 and a transmitter 114,
as well as associated components such as one or more, preferably
embedded or internal, antenna elements 116 and 118, local
oscillators (LOs) 113, and a processing module such as a digital
signal processor (DSP) 120. As will be apparent to those skilled in
the field of communications, the particular design of the
communication subsystem 111 will be dependent upon the
communication network in which the device is intended to operate.
For example, the handheld computing device 100 may include a
communication subsystem 111 designed to operate within the
Mobitex.TM. mobile communication system, the DataTAC.TM. mobile
communication system, GPRS network, UMTS network, EDGE network or
CDMA network.
[0018] Network access requirements will also vary depending upon
the type of network 119. For example, in the Mobitex and DataTAC
networks, the handheld computing device 100 is registered on the
network using a unique identification number associated with each
handheld computing device. In UMTS and GPRS networks, and in some
CDMA networks, however, network access is associated with a
subscriber or user of the handheld computing device 100. A GPRS
handheld computing device therefore requires a subscriber identity
module (SIM) card in order to operate on a GPRS network, and a RUIM
in order to operate on some CDMA networks. Without a valid SIM/RUIM
card, a GPRS/UMTS/CDMA handheld computing device may not be fully
functional. Local or non-network communication functions, as well
as legally required functions (if any) such as "911" emergency
calling, may be available, but the handheld computing device 100
will be unable to carry out any other functions involving
communications over the network. The SIM/RUIM interface 144 is
normally similar to a card-slot into which a SIM/RUIM card can be
inserted and ejected like a diskette or PCMCIA card. The SIM/RUIM
card can have approximately 64K of memory and hold many key
configuration 151, and other information 153 such as
identification, and subscriber related information.
[0019] When required network registration or activation methods
have been completed, the handheld computing device 100 may send and
receive communication signals over the network 119. Signals
received by antenna 116 through communication network 119 are input
to receiver 112, which may perform such common receiver functions
as signal amplification, frequency down conversion, filtering,
channel selection and the like, and in the example system shown in
FIG. 2, analog to digital (A/D) conversion. A/D conversion of a
received signal allows more complex communication functions such as
demodulation and decoding to be performed in the DSP 120. In a
similar manner, signals to be transmitted are processed, including
modulation and encoding for example, by DSP 120 and input to
transmitter 114 for digital to analog conversion, frequency up
conversion, filtering, amplification and transmission over the
communication network 119 via antenna 118. DSP 120 not only
processes communication signals, but also provides for receiver and
transmitter control. For example, the gains applied to
communication signals in receiver 112 and transmitter 114 may be
adaptively controlled through automatic gain control algorithms
implemented in DSP 120.
[0020] The handheld computing device 100 preferably includes a
microprocessor 138 which controls the overall operation of the
device. Communication functions, including at least data and voice
communications, are performed through communication subsystem 111.
Microprocessor 138 also interacts with further device subsystems
such as the display 122, flash memory 124, random access memory
(RAM) 126, auxiliary input/output (I/O) subsystems 128, serial port
130, keyboard 132, speaker 134, microphone 136, a short-range
communications subsystem 140 and any other device subsystems
generally designated as 142.
[0021] Some of the subsystems shown in FIG. 2 perform
communication-related functions, whereas other subsystems may
provide "resident" or on-device functions. Some subsystems, such as
keyboard 132 and display 122, for example, may be used for both
communication-related functions, such as entering a text message
for transmission over a communication network, and device-resident
functions such as a calculator or task list.
[0022] Another such subsystem comprises a power management
subsystem 142 that performs power management functions for the
handheld computing device 100. The power management subsystem 142
will be described in detail below.
[0023] Operating system software used by the microprocessor 138 is
preferably stored in a persistent store such as flash memory 124,
which may instead be a read-only memory (ROM) or similar storage
element (not shown). Those skilled in the art will appreciate that
the operating system, specific device applications, or parts
thereof, may be temporarily loaded into a volatile memory such as
RAM 126. Received communication signals may also be stored in RAM
126.
[0024] As shown, the flash memory 124 can be segregated into
different areas for both computer programs 158 and program data
storage 150, 152, 154 and 156. These different storage areas
indicate that each program can allocate a portion of flash memory
124 for their own data storage requirements. In addition to its
operating system functions, preferably the microprocessor 138
enables execution of software applications on the handheld
computing device. A predetermined set of applications that control
basic operations, will normally be installed on the handheld
computing device 100 during manufacturing.
[0025] One set of basic software applications might perform data
and/or voice communication functions, for example. Another set of
basic software applications comprises computer processing
instructions which, when accessed from the flash memory 124 and/or
the RAM 126 and executed by the microprocessor 138, define a switch
controller 102. The switch controller 102 interacts with the
aforementioned power management subsystem 142 and performs power
management functions. The switch controller 102 will be described
in detail below.
[0026] A preferred software application may be a personal
information manager (PIM) application having the ability to
organize and manage data items relating to the user of the handheld
computing device such as, but not limited to, e-mail, calendar
events, voice mails, appointments, and task items. Naturally, one
or more memory stores would be available on the handheld computing
device to facilitate storage of PIM data items. Such PIM
application would preferably have the ability to send and receive
data items, via the wireless network 119. In a preferred
embodiment, the PIM data items are seamlessly integrated,
synchronized and updated, via the wireless network 119, with the
user's corresponding data items stored or associated with a host
computer system. Further applications may also be loaded onto the
handheld computing device 100 through the network 119, an auxiliary
I/O subsystem 128, serial port 130, short-range communications
subsystem 140 or any other suitable subsystem 142, and installed by
a user in the RAM 126 or preferably a non-volatile store (not
shown) for execution by the microprocessor 138. Such flexibility in
application installation increases the functionality of the device
and may provide enhanced on-device functions, communication-related
functions, or both. For example, secure communication applications
may enable electronic commerce functions and other such financial
transactions to be performed using the handheld computing device
100.
[0027] In a data communication mode, a received signal such as a
text message or web page download will be processed by the
communication subsystem 111 and input to the microprocessor 138,
which preferably further processes the received signal for output
to the display 122, or alternatively to an auxiliary I/O device
128. A user of the handheld computing device 100 may also compose
data items such as email messages for example, using the keyboard
132, which is preferably a complete alphanumeric keyboard or
telephone-type keypad, in conjunction with the display 122 and
possibly an auxiliary I/O device 128. Such composed items may then
be transmitted over a communication network through the
communication subsystem 111.
[0028] For voice communications, overall operation of the handheld
computing device 100 is similar, except that received signals would
preferably be output to a speaker 134 and signals for transmission
would be generated by a microphone 136. Alternative voice or audio
I/O subsystems, such as a voice message recording subsystem, may
also be implemented on the handheld computing device 100. Although
voice or audio signal output is preferably accomplished primarily
through the speaker 134, display 122 may also be used to provide an
indication of the identity of a calling party, the duration of a
voice call, or other voice call related information for
example.
[0029] Serial port 130 in FIG. 2, would normally be implemented in
a personal digital assistant (PDA)-type handheld computing device
for which synchronization with a user's desktop computer (not
shown) may be desirable. The serial port 130 enables a user to set
preferences through an external device or software application and
would extend the capabilities of the handheld computing device 100
by providing for information or software downloads to the handheld
computing device 100 other than through a wireless communication
network.
[0030] Preferably, the serial port 130 comprises a Universal Serial
Bus (USB) port that interfaces with the desktop computer over a USB
cable. The configuration of the serial port 130 as a USB interface
is advantageous since it allows the desktop computer to supply
power to the handheld computing device 100 through the power
management subsystem 142, without requiring a separate power
supply.
[0031] Other communications subsystems 140, such as a short-range
communications subsystem, is a further optional component which may
provide for communication between the handheld computing device 100
and different systems or devices, which need not necessarily be
similar devices. For example, the subsystem 140 may include an
infrared device and associated circuits and components or a
Bluetooth.TM. communication module to provide for communication
with similarly enabled systems and devices.
[0032] FIG. 3 depicts the aforementioned power management subsystem
142. As shown, the power management subsystem 142 comprises a
system power bus 300, a peripheral power bus 302, and an active
switch 304 coupled to the system power bus 300 and the peripheral
power bus 302. The system power bus 300 provides power to the
microprocessor 138, the flash memory 124, the RAM 126, the
auxiliary input/output (I/O) subsystems 128, the communications
subsystem 140 and the device subsystems 142 (including the power
management subsystem 142). The system power bus 300 interfaces with
the power supply channel of the USB port 130, and receives its
power from the desktop computer through a USB cable connected
between the desktop computer and the USB port 130. The system power
bus 300 includes a large system power bus capacitor 306 that
reduces harmonics in the voltage supplied to the system power bus
300 from the USB port 130.
[0033] As shown, the peripheral power bus 302 provides power to the
LCD display 122. The LCD display 122 includes large peripheral
power bus capacitors 308a, 308b that reduce harmonics in the
voltage supplied to the LCD display 122 by the peripheral power bus
302. Alternately, the peripheral power bus capacitors 308 may be
provided directly on the peripheral power bus 302. In either case,
the peripheral power bus capacitors 308 introduce a large
capacitive load on the peripheral power bus 302 that will attempt
to draw a large in-rush current when the LCD display 122 is
powered-up.
[0034] The active switch 304 is disposed electrically in series
between the system power bus 300 and the peripheral power bus 302,
and supplies power to the peripheral power bus 302 from the system
power bus 300. Typically, the voltage required by the LCD display
122 is greater than the system bus voltage. Accordingly, preferably
the active switch 304 acts as a voltage amplifier that provides the
correct operating voltage for the LCD display 122. Preferably, the
active switch 304 comprises a LT 3200-5 charge pump, however other
types of active switches may also be used.
[0035] The switch controller 102 is coupled to a gate input of the
active switch 304, and controls the operation of the active switch
304. The switch controller 102 is configured to regulate the
in-rush current drawn by the peripheral power bus capacitors 308
through the active switch 304.
[0036] The method of operation of the switch controller 102 will
now be described. Initially, a user of the handheld computing
device 100 connects a USB cable between a desktop computer and the
USB port 130 on the handheld computing device 100. Then, the user
depresses the power on/off key 146 on the handheld computing device
100, thereby signalling the switch controller 102 to begin powering
up the display 122.
[0037] As discussed above, the USB standard limits the maximum
current that can be drawn from the USB cable by a low power
bus-powered device to 100 mA (although the source end of the USB
cable may be cable of sourcing a much larger current). However,
ordinarily, the current that is initially drawn by the peripheral
power bus capacitors 308 will greatly exceed that limit, at least
until the peripheral power bus capacitors 308 become charged. Since
the USB standard may require the handheld computing device 100 to
limit its current draw to 100 mA, ordinarily it would not be
possible to power up the handheld computing device 100 from the USB
cable.
[0038] To overcome this problem, the switch controller 102 pulse
width modulates the active switch 304 by applying a periodic gate
signal to the gate input of the active switch 304, which causes the
active switch 304 to periodically open and close. As a result, the
active switch 304 only draws short bursts of current from the
system power bus 300. At the same time, the active switch 304
slowly charges the peripheral power bus capacitors 308 by applying
a corresponding series of short current pulses to the peripheral
power bus 302.
[0039] The pulse width of the periodic gate signal is selected so
that the average current drawn by the handheld computing device 100
is substantially less than that which the handheld computing device
100 would otherwise draw if the active switch 304 was maintained on
continuously. Conversely, the pulse width of the periodic gate
signal is also selected so that the instantaneous voltage at the
system power bus 300 remains above the minimum voltage level
necessary for proper operation of the hardware components powered
by the system power bus 300.
[0040] The switch controller 102 continues to apply the periodic
gate signal to the active switch 304 until the peripheral power bus
capacitors 308 are substantially fully charged. Thereafter, the
switch controller 102 maintains the active switch 304 fully on.
[0041] Since the load characteristics of the LCD display 122 are
known, the maximum time required for the peripheral power bus
capacitors 308 to reach full charge can be determined beforehand.
Accordingly, the switch controller 102 continues to apply the
periodic gate signal to the active switch 304 for the predetermined
maximum time period that would be required for the peripheral power
bus capacitors 308 to become substantially fully charged.
[0042] FIG. 4 depicts the charging waveform for the system power
bus capacitor 306, and the peripheral power bus capacitors 308. As
shown, during the time interval T1, the active switch 304 is off,
which causes system power bus capacitor 306 to charge. The switch
controller 102 then turns the active switch 304 on for the time
interval T2, which causes the peripheral power bus capacitors 308
to charge, and the system power bus capacitor 306 to discharge. The
duration of the time interval T2 is such that the instantaneous
voltage at the system power bus 300 does not fall below the minimum
system voltage.
[0043] During the time interval T3, the switch controller 102 turns
the active switch 304 off, which causes the system power bus
capacitor 306 to charge and the peripheral power bus capacitors 308
to discharge. The duration of the time interval T3 is such that the
instantaneous voltage of the peripheral bus 302 at the end of the
interval T3 is greater than the instantaneous voltage of the
peripheral bus 302 at the start of the interval T3. The switch
controller 102 repeats the charging phases represented by the
charging intervals T2, T3 until the peripheral power bus capacitors
308 become substantially fully charged.
[0044] The present invention is defined by the claims appended
hereto, with the foregoing description being merely illustrative of
a preferred embodiment of the invention. Those of ordinary skill
may envisage certain modifications to the foregoing embodiments
which, although not explicitly discussed herein, do not depart from
the scope of the invention, as defined by the appended claims.
* * * * *