U.S. patent application number 11/754932 was filed with the patent office on 2007-09-27 for methods and apparatus for charging a battery in a peripheral device.
This patent application is currently assigned to Apple Inc.. Invention is credited to Anthony M. Fadell, Christoph Krah.
Application Number | 20070222301 11/754932 |
Document ID | / |
Family ID | 23354224 |
Filed Date | 2007-09-27 |
United States Patent
Application |
20070222301 |
Kind Code |
A1 |
Fadell; Anthony M. ; et
al. |
September 27, 2007 |
METHODS AND APPARATUS FOR CHARGING A BATTERY IN A PERIPHERAL
DEVICE
Abstract
A power manager for managing power delivered to a battery
operated peripheral device is disclosed. The power manager includes
an input current limiter arranged to suppress a power surge
associated with an insertion event by a power cable arranged to
provide an external voltage. A voltage converter unit coupled to
the input current limiter converts the received external voltage to
a supply voltage that is transmitted by way of a main bus to a
voltage sensor unit coupled thereto. During the insertion event, a
comparator unit coupled to the voltage sensor, sends a first
switching signal to a switchover circuit that responds by
connecting the peripheral device and an uncharged battery to the
main bus such that the supply voltage is provided thereto. When the
battery is substantially fully charged, the switchover circuit
responds by electrically disconnecting the battery so as to not
overcharge the battery.
Inventors: |
Fadell; Anthony M.; (Portola
Valley, CA) ; Krah; Christoph; (San Jose,
CA) |
Correspondence
Address: |
BEYER WEAVER LLP/APPLE INC.
P.O. BOX 70250
OAKLAND
CA
94612-0250
US
|
Assignee: |
Apple Inc.
|
Family ID: |
23354224 |
Appl. No.: |
11/754932 |
Filed: |
May 29, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11270901 |
Nov 10, 2005 |
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11754932 |
May 29, 2007 |
|
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10278752 |
Oct 22, 2002 |
6995963 |
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11270901 |
Nov 10, 2005 |
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60345253 |
Oct 22, 2001 |
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Current U.S.
Class: |
307/152 ;
320/148 |
Current CPC
Class: |
H02J 1/06 20130101; H02J
1/001 20200101; H02J 7/00302 20200101; G06F 1/266 20130101; G06F
1/325 20130101; H02J 2207/30 20200101; H02J 7/0031 20130101 |
Class at
Publication: |
307/152 ;
320/148 |
International
Class: |
G01R 19/12 20060101
G01R019/12; H02J 7/04 20060101 H02J007/04 |
Claims
1. An apparatus comprising: a circuit; a battery; a port that
includes a power line and serial data line; and a power management
unit, coupled to the circuit, the battery, and the port, wherein
the power management unit contains instructions that when executed
by the power management unit: (i) powers the circuit with the
battery if the power line does not provide power; (ii) powers the
circuit and charges the battery with power provided by the power
line if the power line provides power to the apparatus.
2. The apparatus of claim 1, wherein the power management unit
further comprises a voltage converter to convert an external power
source voltage to a supply voltage if the external power source
voltage is received through the port and is provided to the
circuit.
3. The apparatus of claim 2, wherein the voltage converter of the
power management unit is a step down converter configured to step
down the external power supply voltage to the supply voltage.
4. The apparatus of claim 2, wherein the power management unit
further comprises a charge current generator to generate a charge
current to charge the battery if the external power supply voltage
is received through the port and a battery power source voltage is
below the supply voltage by a threshold.
5. The apparatus of claim 4, wherein the power management circuit
further comprises a comparator to compare the battery power source
voltage to the supply voltage.
6. The apparatus of claim 5, wherein the comparator generates a
first signal if the battery power source voltage is within the
threshold from the supply, the first signal provided to a charge
control circuit.
7. The apparatus of claim 6, wherein the first signal further
causes the charge circuit to disconnect the external power supply
voltage from the battery to prevent over-charging of the
battery.
8. The apparatus of claim 5, wherein the comparator generates a
second signal if the battery power source voltage is below the
threshold of the supply voltage, the second signal causing a charge
circuit to generate a charge current to charge the battery when the
external power supply voltage is received through the port.
9. The apparatus of claim 2, wherein the supply voltage is one of
the following voltages: approximately 1.8 volts, approximately 3.3
volts, approximately 5.0 volts; or 5.0 volts or less.
10. The apparatus of claim 1, wherein the power management unit
further comprises a switch circuit configured to prevent
substantial interruptions in providing power to the circuit when
switching from the external power supply voltage to the battery
power source voltage or vice versa.
11. The apparatus of claim 1, wherein the port is configured to
receive at least one power line.
12. The apparatus of claim 1, wherein the port is configured to
receive at least one data line arranged to form a
transmit-and-receive connection with the external source.
13. A method for providing power to a circuit contained within a
portable device from either a battery contained in the device or an
external power source when plugged into a port configured to
receive both power and data at the device, the method comprising:
ascertaining if the external power source is plugged into the port
of the device, and either: (i) providing power to the circuit from
the battery when the external power source is not plugged into the
device; (ii) providing power from the external power source to the
circuit and the battery used to at least recharge the battery when
the external power source is plugged into the device and when the
output of the battery is below a supply voltage by more than a
threshold; or (iii) providing power from the external power source
only to the circuit when the external power source is plugged into
the device and the output of the battery is within the threshold of
the supply voltage.
14. The method of claim 13, further comprising converting an
external power source voltage to the supply voltage within the
device, wherein the supply voltage is one of the following:
approximately 1.8 volts, approximately 3.3 volts, approximately 5.0
volts; or 5.0 volts or less.
15. The method of claim 14, wherein providing the external power to
the circuit in the device and the battery to recharge the battery
further comprises generating a charge current to charge the battery
when an output voltage of the battery is below the supply voltage
by more than the threshold.
16. The method of claim 15, further comprising comparing the
battery voltage output to the supply voltage and either: (i)
generating a first signal if the battery voltage output is within
the threshold from the supply voltage, the first signal causing
power from the external power supply to be provided only to the
circuit when the external power is received through the port; or
(ii) generating a second signal if the battery voltage output is
below the threshold of the supply voltage, the second signal
causing a charge current to be provided to the battery to charge
the battery when the external power is received through the
port.
17. The method of claim 15, further comprising disconnecting the
external power supply voltage from the battery after the battery is
charged.
18. The method of claim 15, further comprising switching between
(i), (ii) and (iii) such that power provided to the circuit from
either the battery or the external power source voltage is
substantial without interruption.
19. The method of claim 15, further comprising transmitting and/or
receiving data through the port of the device.
20. A battery powered device comprising: a rechargeable battery; a
serial port that interfaces with a serial bus cable for
transmitting data to or from the device that includes a plurality
of data pins and at least a power pin; a voltage sensor that senses
a voltage on the power pin; and a battery charging circuit that
draws a charging current through the power pin of the serial port
to charge the battery when the battery is substantially
uncharged.
21. The battery powered device of claim 20, wherein the device
comprises a personal digital assistant.
22. The battery powered device of claim 20, wherein the device
comprises a personal MP3 player.
23. The battery powered device of claim 20, wherein the
rechargeable battery comprises a lithium ion cell.
24. The battery powered device of claim 20, wherein the
rechargeable battery operates within a voltage range of 3.7 volts
to 4.2 volts.
25. The battery powered device of claim 20, wherein the serial port
interfaces with a serial bus cable that transmits data to or from
the device at a rate of at least 100 megabits per second.
26. The battery powered device of claim 20, wherein the serial port
interfaces with a serial bus cable transmits data to or from the
device in an asynchronous or isochronous mode.
27. The battery powered device of claim 20, wherein the serial port
interfaces with an IEEE 1394 compliant serial bus cable.
28. The battery powered device of claim 20, wherein the battery
charging circuit operates in a constant current mode.
29. The battery powered device of claim 20, wherein the battery
charging circuit shuts off when its supply voltage is less than 4.2
volts.
30. The battery powered device of claim 20, wherein the battery
charging circuit electrically isolates the battery if the battery
is fully charged.
31. The battery powered device of claim 20, wherein the charging
current is 750 mA.
32. The battery powered device of claim 20, wherein the voltage
sensor and the battery charging circuit are coupled to the serial
port via a main bus.
33. The battery powered device of claim 20, further comprising an
inrush current limiter configured to limit an inrush current that
flows into the battery powered device when a serial bus cable is
inserted into the serial port.
34. The battery powered device of claim 20, further comprising a
voltage converter configured to convert an external voltage
received at the power pins of the serial port to an internal supply
voltage within the range of 1.8 volts to 5 volts.
35. The battery powered device of claim 20, further comprising an
active circuit operating at a supply voltage within the range of
1.8 volts to 5 volts.
36. The battery powered device of claim 20, further comprising a
comparator coupled to the voltage sensor and configured to generate
a switching signal based upon the sensed voltage.
37. The battery powered device of claim 20, further comprising a
switchover circuit configured to supply power to an active circuit
via the battery or a supply voltage received via the power pins of
the serial port.
38. A method for charging a battery of a peripheral device,
comprising: inserting a serial bus cable into a serial port of the
peripheral device, the serial port comprising a power pin and a
plurality of data pins through which data can be transmitted to or
from the peripheral device; sensing that the voltage at the power
pin of the serial port is above a selected threshold; and drawing a
charge current through the power pin of the serial port to charge
the battery of the peripheral device.
39. The method of claim 38, wherein the peripheral device comprises
a personal digital assistant.
40. The method of claim 38, wherein the peripheral device comprises
a personal MP3 player.
41. The method of claim 38, wherein the battery operates within a
voltage range of 3.7 volts to 4.2 volts.
42. The method of claim 38, wherein the battery is considered to be
uncharged when its voltage drops below 3.45 volts.
43. The method of claim 38, wherein the serial port interfaces with
a serial bus cable that transmits data to or from the device in an
asynchronous or isochronous mode.
44. The method of claim 38, wherein the serial port interfaces with
an IEEE 1394 serial bus cable.
45. The method of claim 38, wherein the charge current is 750
mA.
46. The method of claim 38, further comprising electrically
isolating the battery if the battery is substantially fully
charged.
47. The method of claim 38, further comprising suppressing a power
surge caused by the insertion of the serial bus cable into the
serial port.
48. The method of claim 38, further comprising converting an
external voltage received at the power pins of the serial port to
an internal supply voltage within the range of 1.8 volts to 5
volts.
49. A system comprising: a battery powered device having a
rechargeable battery and a battery charging circuit; and a serial
bus cable coupled to the battery powered device, the serial bus
cable comprising a power transmission line and a plurality of data
transmission lines, wherein the serial bus cable can transmit data
to or from the battery powered device over the data transmission
lines; and wherein the battery charging circuit of the battery
powered device draws a charging current through the power
transmission line of the serial bus cable if the rechargeable
battery is not fully charged.
50. The system of claim 49, wherein the battery powered device
comprises a personal digital assistant.
51. The system of claim 49, wherein the battery powered device
comprises a personal MP3 player.
52. The system of claim 49, wherein the rechargeable battery
operates within a voltage range of 3.7 volts to 4.2 volts.
53. The system of claim 49, wherein the serial bus cable transmits
data to or from the battery powered device at a rate of at least
100 megabits per second.
54. The system of claim 49, wherein the serial bus cable transmits
data to or from the battery powered device in an asynchronous or
isochronous mode.
55. The system of claim 54, wherein the serial bus cable comprises
an IEEE 1394 compliant serial bus cable.
56. The system of claim 49, wherein the battery powered device
electrically isolates the rechargeable battery when the battery is
fully charged.
57. The system of claim 49, wherein the charging current is 750
mA.
58. The system of claim 49, wherein the battery powered device
comprises an active circuit operating at a supply voltage within
the range of 1.8 volts to 5 volts.
59. The system of claim 49, wherein the data transmission lines are
separately-shielded twisted transmission type data lines.
60. A method for managing power delivered to a battery-operated
peripheral device by way of a cable that includes a number of lines
at least one of which is a power line arranged to carry electrical
power from an electrical supply to the device, the method
comprising: detecting a status for the device, wherein the status
is based on whether a first condition relating to a battery in the
device has occurred and whether a second condition relating to
connection of the cable to the electrical supply has occurred;
drawing electrical power from the electrical supply at a first
current if the device has a first status; and drawing electrical
power from the electrical supply at a second current level if the
device has a second status.
61. The method of claim 60, wherein the second condition is the
attachment of the cable to another device.
62. The method of claim 60, wherein the second condition is the
connection of the cable to another device such that a data transfer
request is received by the battery-operated peripheral device.
63. The method of claim 60, further comprising converting the
electrical power from an external voltage to a supply voltage by a
voltage converter unit.
64. The method of claim 60, wherein the first condition is when a
battery in the device is fully charged.
65. The method of claim 64, further comprising, if the battery is
fully charged, providing the battery with electrical power from the
electrical supply at a third current level.
66. The method of claim 65, wherein the third current level is
essentially zero amps.
67. The method of claim 65, wherein the cable includes two twisted
pairs of wires carrying data.
68. The method of claim 67, wherein the two twisted pairs of wires
are separately shielded.
69. The method of claim 68, wherein the cable is an I.E.E.E. 1394
compliant cable.
70. A portable consumer electronic product comprising: a sensor
unit arranged to detect a status for the device, wherein the status
is based on whether a first condition relating to a battery in the
device has occurred and whether a second condition relating to
connection of the cable to the electrical supply has occurred; a
switchover circuit arranged to draw electrical power from the
electrical supply at a first current if the device has a first
status, and to draw electrical power from the electrical supply at
a second current level if the device has a second status.
71. The portable consumer electronic product of claim 70, further
comprising a voltage converter unit arranged to convert the
electrical power from an external voltage to a supply voltage.
72. The portable consumer electronic product of claim 70, wherein
the switchover circuit is further arranged to, if the battery is
fully charged, provide the battery with electrical power from the
electrical supply at a third current level.
73. The portable consumer electronic product of claim 70, wherein
the third current level is essentially zero amps.
74. The portable consumer electronic product of claim 70, wherein
the cable includes two twisted pairs of wires carrying data.
75. The portable consumer electronic product of claim 74, wherein
the two twisted pairs of wires are separately shielded.
76. The portable consumer electronic product of claim 75, wherein
the cable is an I.E.E.E. 1394 compliant cable.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/270,901 (Attorney Docket APL1P224C1)
entitled "METHODS AND APPARATUS FOR CHARGING A BATTERY IN A
PERIPHERAL DEVICE," filed Nov. 10, 2005, which is a continuation of
U.S. patent application Ser. No. 10/278,752 (Attorney Docket
APL1P224) entitled "METHODS AND APPARATUS FOR CHARGING A BATTERY IN
A PERIPHERAL DEVICE" filed Oct. 22, 2002 and which issued as U.S.
Pat. No. 6,995,963 on Feb. 27, 2006, which are incorporated herein
by reference, and which, in turn, claim the benefit of priority
under 35 U.S.C. .sctn. 119(e) to U.S. Provisional Patent
Application No. 60/345,253, entitled "METHODS AND APPARATUS FOR
CHARGING A BATTERY IN A PERIPHERAL DEVICE VIA A FIREWIRE CABLE"
filed on Oct. 22, 2001, which is incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of Invention
[0003] This invention relates generally to computing systems.
Specifically, a method and apparatus for managing power delivered
by way of a FireWire cable to a battery operated peripheral
device.
[0004] 2. Description of Related Art
[0005] FireWire is an IEEE1394 compliant High Performance Serial
Bus that provides two types of data transfer: asynchronous and
isochronous. Asynchronous is for traditional load-and-store
applications where data transfer can be initiated and an
application interrupted as a given length of data arrives in a
buffer. Isochronous data transfer ensures that data flows at a
pre-set rate so that an application can handle it in a timed way
while providing the bandwidth needed for audio, imaging, video, and
other streaming data. Isochronous service means it guarantees
latency or the length of time between a requested action and when
the resulting action occurs which is a critical feature in
supporting real time video, for example. FireWire provides a
high-speed serial bus with data transfer rates of 100, 200, or 400
Mbps as well as a single plug-and-socket connection on which up to
63 devices can be attached with data transfer speeds up to 400 Mbps
(megabits per second). In this way, FireWire offers a standard,
simple connection to all types of consumer electronics, including
digital audio devices, digital VCRs and digital video cameras; as
well as to traditional computer peripherals such as optical drives
and hard disk drives.
[0006] The standard FireWire cable consists of six wires in which
data is sent via two separately-shielded twisted pair transmission
lines that are crossed in each cable assembly to create a
transmit-receive connection. Two more wires carry power (8 to 28 v,
1.5 A max.) to remote devices. In some cases, such as with DV
camcorders manufactured by the Sony Corporation of Japan, a 4
conductor FireWire cable is used (configured as the 6 wire cable
but without the power wires) that terminate in smaller, 4 prong
connectors. To connect a four prong device, such as the Sony DV
camcorder with a standard IEE1394 FireWire device or interface
card, an adapter cable is required having 4 prongs on one side and
6 on the other. In this way, the data lines are connected while
omitting the power connection.
[0007] In those situations, however, when a battery operated six
prong peripheral device is coupled to a FireWire cable, it is
important for the power delivered to the device (typically 1.8 v,
3.3, or 5.0 v) to be both stable and reliable especially when the
FireWire cable is either connected or disconnected.
[0008] Therefore, what is required is a method and apparatus for
managing power delivered by way of a FireWire cable to a battery
operated peripheral device.
SUMMARY OF THE INVENTION
[0009] According to the present invention, methods, apparatus, and
systems are disclosed for managing power in a battery powered
portable device is disclosed.
[0010] In one embodiment, an apparatus is described that includes
at least a circuit, a battery, a port that includes a power line
and serial data line, and a power management unit, coupled to the
circuit, the battery, and the port. In the described embodiment,
the power management unit contains instructions that when executed
by the power management unit: (i) powers the circuit with the
battery if the power line does not provide power; and (ii) powers
the circuit and charges the battery with power provided by the
power line if the power line provides power to the apparatus.
[0011] In another embodiment, a method for providing power to a
circuit contained within a portable device from either a battery
contained in the device or an external power source when plugged
into a port configured to receive both power and data at the
device, the method is carried out by performing at least the
following operations. Ascertaining if the external power source is
plugged into the port of the device, and either: providing power to
the circuit from the battery when the external power source is not
plugged into the device, or providing power from the external power
source to the circuit and the battery used to at least recharge the
battery when the external power source is plugged into the device
and when the output of the battery is below a supply voltage by
more than a threshold, or providing power from the external power
source only to the circuit when the external power source is
plugged into the device and the output of the battery is within the
threshold of the supply voltage.
[0012] In still another embodiment, a battery powered device is
described that includes at least a rechargeable battery, a serial
port that interfaces with a serial bus cable for transmitting data
to or from the device that includes a plurality of data pins and at
least a power pin, a voltage sensor that senses a voltage on the
power pin, and a battery charging circuit that draws a charging
current through the power pin of the serial port to charge the
battery when the battery is substantially uncharged.
[0013] In still another embodiment, a method for charging a battery
of a peripheral device, is described. The method is carried out by
performing at least the following operations: inserting a serial
bus cable into a serial port of the peripheral device, the serial
port comprising a power pin and a plurality of data pins through
which data can be transmitted to or from the peripheral device,
sensing that the voltage at the power pin of the serial port is
above a selected threshold, and drawing a charge current through
the power pin of the serial port to charge the battery of the
peripheral device.
[0014] Another embodiment describes a system that includes a
battery powered device having a rechargeable battery and a battery
charging circuit, and a serial bus cable coupled to the battery
powered device where the serial bus cable includes at least a power
transmission line and a plurality of data transmission lines and
can transmit data to or from the battery powered device over the
data transmission lines. The battery charging circuit of the
battery powered device draws a charging current through the power
transmission line of the serial bus cable if the rechargeable
battery is not fully charged.
[0015] A method for managing power delivered to a battery-operated
peripheral device by way of a cable that includes a number of lines
at least one of which is a power line arranged to carry electrical
power from an electrical supply to the device is also described.
The method includes at least the following operations: detecting a
status for the device, wherein the status is based on whether a
first condition relating to a battery in the device has occurred
and whether a second condition relating to connection of the cable
to the electrical supply has occurred, drawing electrical power
from the electrical supply at a first current if the device has a
first status, and drawing electrical power from the electrical
supply at a second current level if the device has a second
status.
[0016] A portable consumer electronic product includes a sensor
unit arranged to detect a status for the device, wherein the status
is based on whether a first condition relating to a battery in the
device has occurred and whether a second condition relating to
connection of the cable to the electrical supply has occurred, and
a switchover circuit arranged to draw electrical power from the
electrical supply at a first current if the device has a first
status, and to draw electrical power from the electrical supply at
a second current level if the device has a second status.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The invention will be better understood by reference to the
following description taken in conjunction with the accompanying
drawings.
[0018] FIG. 1A shows a power manager unit with a fully discharged
battery coupled to an active FireWire cable in accordance with an
embodiment of the invention.
[0019] FIG. 1B shows the power manager unit of FIG. 1A where the
battery is fully charged in accordance with an embodiment of the
invention.
[0020] FIG. 1C shows the power manager unit of FIG. 1B where the
FireWire cable of the invention.
[0021] FIG. 3 shows an exemplary response waveforms for the
switchover state where the battery is fully charged.
[0022] FIGS. 4 and 5 show exemplary response waveforms for the
switchover state where the battery is full and the Fire Wire is
unplugged in two separate scenarios.
[0023] FIG. 6 shows an exemplary response waveforms for the
switchover state where the battery is low and the FireWire is
plugged.
[0024] FIG. 7 shows an exemplary response waveforms for the
switchover state where the battery is low and the FireWire is
unplugged.
[0025] FIG. 8 shows an exemplary response waveforms for the
switchover state where the battery is empty and the FireWire is
plugged.
[0026] FIG. 9 shows an exemplary response waveforms for the
switchover state where the battery is empty and the FireWire is
unplugged.
DETAILED DESCRIPTION OF SELECTED EMBODIMENTS
[0027] Reference will now be made in detail to a preferred
embodiment of the invention. An example of the preferred embodiment
is illustrated in the accompanying drawings. While the invention
will be described in conjunction with a preferred embodiment, it
will be understood that it is not intended to limit the invention
to one preferred embodiment. To the contrary, it is intended to
cover alternatives, modifications, and equivalents as may be
included within the spirit and scope of the invention as defined by
the appended claims.
[0028] In a battery powered FireWire compatible device, a method
and apparatus for supplying power to the device that can be used to
either operate the device of charge the device's battery are
described. In one embodiment, various power signals on a FireWire
data bus coupled to the device, provide for operating the device
and/or charging the device's internal battery over a prescribed
range of supply voltages. In a particular embodiment, the apparatus
includes a built in surge suppression unit as well as a FireWire
power/battery switchover unit to ensure that a stable and reliable
power supply is provided the device. In this way, additional power
connectors are substantially eliminated thereby saving product cost
and reducing product size.
[0029] The invention will now be described in terms a FireWire
peripheral power management unit suitable for supplying power to
any FireWire compatible device. Such devices include, for example,
personal digital assistants, personal MP3 player/recorders, and the
like.
[0030] Accordingly, FIG. 1A shows a power manager unit 100 with a
fully discharged battery coupled to an active FireWire cable in
accordance with an embodiment of the invention. The power manager
unit 100 includes an input current limiter 102 for suppressing a
power surge caused by a FireWire cable insertion event related to
voltage transients (i.e., ground bounce) associated with an
insertion of a powered FireWire cable 104 to an input port 106. It
should be noted, that this phenomenon is only applicable to those
peripheral devices capable of receiving a FireWire cable having a
power wire included therein (such as a six prong type FireWire
cable). The input current limiter 102 is, in turn, coupled to a
voltage converter unit 108 having an output 108' arranged to
convert a received external voltage V.sub.ext (in the form of a
FireWire voltage V.sub.FW having a range of between 8 volts and 28
volts provided by the FireWire cable 104) to a supply voltage
V.sub.cc provided to a main bus 110. Typically, the supply voltage
V.sub.cc can be approximately 1.8 volts, approximately 3.3 volts,
or approximately 5.0 volts each of which is suitable for driving an
active circuit 112 included in a battery operated peripheral device
113.
[0031] In the described embodiment, the voltage converter unit 108
is coupled to a voltage sensor 114 arranged to provide a voltage
signal V.sub.sig to a comparator unit 116. The comparator unit 116,
based upon the voltage signal V.sub.sig, provides a switchover
signal V.sub.switch to a switchover circuit 118. In those cases
where the voltage signal V.sub.sig is above a voltage threshold
V.sub.th (indicative of a FireWire insertion event having had
occurred at the input port 106), the comparator unit 116 provides a
first switchover signal V.sub.switch1 to the switchover circuit
118. The switchover circuit 118, in turn, responds to the first
switchover signal V.sub.switch1 by connecting the main bus 110 to
the active circuit 112 (and thereby the supply voltage V.sub.cc)
and to a battery 120 when the battery 120 is substantially
uncharged so as to provide a charging current to the battery 120.
As shown in FIG. 1B, in those cases where the battery 120 is
substantially fully charged, the comparator circuit 116 sends a
second switchover signal V.sub.switch2 that causes the switchover
circuit 118 to disconnect the battery 120 from the main bus 110 so
as to avoid overcharging the battery 120.
[0032] In those situations shown in FIG. 1C where the powered
FireWire cable 104 has been disconnected from the port 106, the
voltage signal V.sub.sig is below the voltage threshold V.sub.th to
which the comparator circuit 116 responds by providing a third
switchover signal V.sub.switch3 to the switchover circuit 118. The
switchover circuit 118 responds to the third switchover signal
V.sub.switch3 by disconnecting the main bus 110 from the active
circuit 112 and connecting the battery 120 in such a manner as to
provide a substantially uninterrupted supply voltage V.sub.cc to
the active circuit 112.
[0033] Referring to FIG. 2, the switchover circuit 118 includes a
comparator 202 that helps to ensure a smooth transition from
battery to FireWire power and vice versa. The switch over circuit
118 ensures that the voltage on the main supply bus 110 (VCC_MAIN)
doesn't drop below a pre-determined minimum voltage V.sub.min (at
which point a reset signal is typically provided). Accordingly, the
FireWire voltage converter 108 switches in/out when the voltage on
the main bus 110 (V.sub.cc MAIN) has risen/dropped above/below
V.sub.min.
[0034] FIG. 3 shows an exemplary response waveforms for the
switchover state where the battery is full and the FireWire is
plugged in. After the FireWire cable 104 is plugged into the port
106, the output of the FireWire voltage converter 108 reaches its
destination voltage within 15 ms. When the output of the FireWire
voltage converter 108 reaches the switch over threshold
V.sub.switch, the comparator 202 disconnects battery power from the
main supply bus 110. For a short period of time, neither the
battery 120 nor the FireWire voltage converter 108 supply power to
VCC_MAIN 110 and the voltage on VCC_MAIN 110 will drop until either
of the voltage sensor 114 starts conducting such that the voltage
cannot drop below the voltage V.sub.MIN. Eventually the voltage
sensor 114 starts conducting, pulling the voltage on bus 110 up to
a pre-set voltage drop V.sub.f below the destination output voltage
of the FireWire voltage converter 108.
[0035] FIGS. 4 and 5 show an exemplary response waveforms for the
switchover state where the battery is full and the FireWire is
unplugged in two separate scenarios. Initially, the voltage
V.sub.VCC.sub.--.sub.MAIN is V.sub.f below the voltage of the
FireWire voltage converter 108. Due to the system load, the output
voltage of the FireWire voltage converter 108 is going to drop
rapidly as the voltage sensor 114 discharges into the main supply
bus 110. When FireWire 106 is unplugged the voltage at the output
of the FireWire voltage converter 108 is going to drop rapidly
until the voltage sensor 114 starts conducting. At this point the
voltage at the output of the FireWire voltage converter 108 may or
may not have not dropped below the switch over threshold Vswitch.
There will be two possible scenarios:
[0036] In one scenario shown in FIG. 4, the comparator threshold
has been crossed in which case, the battery 120 has to make up for
the voltage V.sub.f. In a second scenario shown in FIG. 5, the
comparator threshold has not been crossed.
[0037] FIG. 6 shows an exemplary response waveforms for the
switchover state where the battery is low and the FireWire is
plugged. In the described embodiment, the battery is considered
empty when it's voltage drops below 3.45V. For the purpose of this
discussion only therefore, the battery voltage is considered to be
at 3.3V. If the battery voltage drops below 3.45V the system is
turned off and less than 2 mA are drawn from the battery. Therefore
the voltage the main bus 110 is approximately equal to the battery
voltage V.sub.BAT=3.3V. After the FireWire connector 104 is plugged
into the port 106, output 108' increases. If output 108' increases
above V.sub.VCC.sub.--.sub.MAIN of 3.3V, the voltage sensor 114
starts conducting. The battery will be back fed from then on, until
output 108' reaches the switch over threshold.
[0038] FIG. 7 shows an exemplary response waveforms for the
switchover state where the battery is low and the FireWire is
unplugged. Initially, the voltage V.sub.VCC.sub.--.sub.MAIN on the
main bus 110 is V.sub.f below the voltage of the FireWire voltage
converter 108 resulting in the output 108' dropping off rapidly.
When output 108' drops below the switch over threshold
V.sub.switch, voltage converter 108 is going to back feed into the
battery until output 108' drops below a level where voltage sensor
114 loses conduction. If the latter occurs, output 108' is going to
be discharged much slower as it is disconnected from the rest of
the system. It has to be noted that this particular scenario is
very rare as the battery voltage recovers within short periods of
time to a level that is above the 3.45V system shut down
threshold.
[0039] FIG. 8 shows an exemplary response waveforms for the
switchover state where the battery is empty and the FireWire is
plugged. When the battery is empty, V.sub.VCC.sub.--.sub.MAIN is
initially approximately ground level and the battery charger
circuit is disabled. If output 108' charges up,
V.sub.VCC.sub.--.sub.MAIN is approximately one diode forward
voltage drop below output 108'. (It should be noted that a reset
circuit keeps the system 100 in constant reset below voltages of
3.135V) thereby enabling a battery charger circuit. If battery
charger circuit supply voltage has exceeded the lockout voltage of
4.1V, battery back feeding is prevented because the battery 120 is
disconnected from the system 100. The battery charger is activated
when it's supply voltage exceeds the under voltage lock out
threshold of 4.1V. To enable the battery charger, the voltage at
the output of the FireWire voltage converter 108 must be one
forward diode drop above the lock out voltage of the battery
charger. Therefore, output 108' has to rise above approximately
4.6V to activate the charger.
[0040] FIG. 9 shows an exemplary response waveforms for the
switchover state where the battery is empty and the FireWire is
unplugged. When the battery is empty and FireWire 104 is unplugged,
the system 100 will run until VCC_MAIN drops rapidly below reset
threshold voltage V.sub.reset,TH. In reset, the battery disconnect
circuitry disconnects the battery from the system 100 when the
battery voltage drops below 3.1V to avoid deep discharge of the
battery using a low voltage disconnect circuitry.
[0041] Although only a few embodiments of the present invention
have been described, it should be understood that the present
invention may be embodied in many other specific forms without
departing from the spirit or the scope of the present invention.
Therefore, the present examples are to be considered as
illustrative and not restrictive, and the invention is not to be
limited to the details given herein, but may be modified within the
scope of the appended claims along with their full scope of
equivalents.
[0042] While this invention has been described in terms of a
preferred embodiment, there are alterations, permutations, and
equivalents that fall within the scope of this invention. It should
also be noted that there are many alternative ways of implementing
both the process and apparatus of the present invention. It is
therefore intended that the invention be interpreted as including
all such alterations, permutations, and equivalents as fall within
the true spirit and scope of the present invention.
* * * * *