WO2011015900A1

WO2011015900A1 - A battery pack with integral dc-dc converter(s)

Info

Publication number: WO2011015900A1
Application number: PCT/IB2009/053410
Authority: WO
Inventors: Pavel Novoselov
Original assignee: Nxp B.V.
Priority date: 2009-08-05
Filing date: 2009-08-05
Publication date: 2011-02-10
Also published as: CN102484292A; EP2462651A1

Abstract

A battery pack, for use with portable of mobile devices, is disclosed which comprises an integral DC-DC converter in addition to the Li-ion battery. The DC-DC converter is capable of providing an output voltage which is higher than the direct output of the Lithium-ion battery. In a particularly preferred embodiment, the battery-pack further comprises at least one further DCDC converter to provide a second output voltage, which is different to the first output voltage.

Description

DESCRIPTION

A BATTERY PACK WITH INTEGRAL DC-DC CONVERTER(S)

Field of the Invention This invention relates to battery packs for mobile of portable devices, and in particular to such battery packs which comprise batteries having lithium- ion or lithium solid state cells.

Background of the Invention

One of the most important factors affecting the performance of many mobile or portable devices is the length of time for which the device may be used without having to either replace or recharge its battery. Before the advent and widespread adoption of Nickel Cadmium (Ni-Cad) rechargeable batteries, traditional mobile and portable devices used non-rechargeable alkaline batteries; however, for many categories of portable devices, these have now been completely supplanted by rechargeable batteries which avoid the expense and environmental implications of the replacement and disposal of used or discharged batteries or cells.

In recent years there has been an increasing trend away from Ni-Cad towards the use of lithium-ion, or solid state lithium, batteries. In addition to greatly superior energy-storage-to-mass and energy-storage-to-volume ratios, lithium-ion batteries have the advantage of being able to be manufactured into almost any form or shape. This is particularly convenient for portable devices such as mobile phones which have a small form factor and limited space available for the battery. As a result, lithium ion batteries now account for the vast majority of rechargeable batteries used in devices such as mobile phones, PDAs, personal communicators and the like. However, the operational characteristics of the lithium ion batteries are not the same as those of the previously used Ni-Cad battery. This has resulted in significant changes to the power management systems of portable and mobile devices. The output voltage of a fully charged Ni-Cad cell falls rapidly initially, from its fully charged voltage to a relatively stable operational voltage, and thereafter remain relatively constant; only when the NiCad cell is almost fully discharged does the voltage is again started to drop rapidly. In contrast, a lithium-ion cell, when fully charged, may have an output voltage of approximately 4.2V; the output voltage falls linearly during operation, until it reaches a voltage of approximately 2.5 V, when effectively the lithium-ion cell is fully discharged.

Hence a 2-cell lithium-ion battery may provide an operational output voltage which varies between 8.4 and 5.0 V; this presents significant challenges for the design of the power management system.

The UK patent application publication GB2,270,793A1 discloses a method of addressing the problem of the variability of output voltage, by including within a lithium-ion battery pack a DC-DC converter which converts the variable direct output voltage from the lithium-ion battery into a fixed, lower, voltage. The voltage may be pre-selected. The DC-DC converter accommodates the variability of the direct output voltage from the battery, and presents the mobile of portable device with a stable voltage. There remains an ongoing need for a battery pack, which can supply a stable voltage which is higher than the almost discharged voltage level from the lithium-ion battery.

Furthermore, many modern portable devices such as mobile phones are capable of performing a wide variety of functions. The individual units which provide these functions each require electrical power, and the optimum voltage requirements for each of the individual units may differ: for example, a display may require a voltage between 5 and 10V, in order to power both the display itself and any required back light; similarly a flash unit may require a high voltage; a CPU made in contrast only require a voltage between 1.5 and 2.5V. The power management system for such portable devices often comprises several DC-DC converters to provide different voltages. In particular, an up-converter may be required to provide a higher voltage for a display system, and one or more down-converters may be required in order to supply suitable driver voltages for a CPU system. Furthermore, some of the functional units may require close control of their input voltage, so a dedicated DC-DC converter may be integrated into that functional unit, even where the same nominal voltage is available elsewhere in the device. Since the power management system has to provide several different voltages, some of which may be either above or below the output voltage from the battery pack, depending on the state charge of the battery pack, it will be appreciated that there is significant complexity to the power management system. There is thus an ongoing need for solutions which can simplify the power management systems for such portable and mobile devices.

Summary of the invention

It is an object of the present invention to provide a battery pack which can eliminate or alleviate the above problems associated with the variable voltage output from lithium-ion battery packs.

According to the present invention there is provided a battery pack for use with a portable device, the battery pack comprising one or a plurality of lithium-ion cells providing a first voltage, a DC-DC converter operable under control of a control unit and for converting the first voltage into a second voltage, an interface unit for receiving, in use, information from the portable device and supplying information to the control unit, the control unit being for controlling the DC-DC converter in response to the interface unit, wherein the DC-DC converter is adapted such that the second voltage can be greater than the first voltage. Thus, the battery Pack according to a first embodiment of the invention provides a solution to the above problem in that it can provide a voltage which is higher than the direct output voltage from the lithium-ion battery. The DC-DC converter may be any suitable type of converter, including either a boost converter or a buck-boost converter, and conveniently is an inexpensive capacitive converter.

In a particularly preferred embodiment, the battery pack further comprises at least one further DC-DC converter operable under control of the control unit, for converting the first voltage into at least one further voltage which is different from the second voltage. Alternatively, the DC-DC converter may be a multi-output DC-DC converter adapted to further convert the first voltage into at least one further voltage which is different from the second voltage. Thus, in these particularly convenient embodiments, the battery pack is able to provide multiple voltages, in order to supply functional units within a portable device which operate at different voltages. Advantageously, this can reduce the overall number of components in the portable device, and since the solution concentrates more of the power management function within the battery pack, allows for significantly improved design of the device itself. In particular, since the variability in output voltage of the lithium-ion battery is handled within the battery pack, it is not necessary to handle this within the portable device. The controller may control the magnitude of at least one of the second voltage and the at least one further voltage. Thus the battery pack may be able to supply an output voltage or voltages, the magnitude of level of which are context specific: the context may be a temporary device state (such as charging a capacitor for a flash-discharge), or may be portable device-specific (so that the battery pack is compatible with portable devices which each require a different set of supply voltages. The interface unit may a digital interface unit. A digital interface unit provide a convenient and rugged means of communicating information to and from the battery pack. Such information can include, for instance, information on the state of charge of the battery pack, thus allowing the portable device to selectively switch-off higher power functions such as flash units, or LED torch functions, in order to conserve the remaining battery life for more essential functions. Furthermore, such a digital interface can conveniently communicate device information to the battery pack, for instance, information as to whether particular voltage output is required by the device, so that the control unit may switch off un-needed DC-DC converters.

The interface unit may further comprise at least one V-sense input for receiving voltage sense information from the portable device. Inclusion of V- sense (also known as Kelvin probes or zero-current sensors) information is particularly useful to ensure that an accurate voltage is supplied to the relevant functional unit in the device, and that compensation can be made for ohmic losses due to wiring/ routing etc. Since the DC-DC conversion is centralised in the battery pack, rather than distributed to immediately adjacent (or within) the appropriate functional unit, such losses may be significant, and it is particularly useful to be able to provide a means whereby they can be compensated.

These and other aspects of the invention will be apparent from, and elucidated with reference to, the embodiments described hereinafter.

Brief description of Drawings

Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which

Figure 1 illustrates part of a conventional power management system for a portable device; Figure 2 is a schematic of the power routing configuration of a battery pack according to an embodiment of the invention; and

Figure 3 is a schematic of a battery pack arranged according to an embodiment of the invention.

It should be noted that the Figures are diagrammatic and not drawn to scale. Relative dimensions and proportions of parts of these Figures have been shown exaggerated or reduced in size, for the sake of clarity and convenience in the drawings. The same reference signs are generally used to refer to corresponding or similar feature in modified and different embodiments

Detailed description of embodiments

Figure 1 illustrates part of a conventional power management system for a portable device. The power management system includes a lithium-ion battery 102 within a battery pack 103. The battery pack provides a variable output voltage, which is distributed via links 105 to several DC-DC converters. The DC-DC converters may include a down-converter 110 which powers a voltage bus 120 providing voltage to power one or more functional units 106 and 107 of the portable device. Furthermore, the DC-DC converters may include converters which are specific to a particular functional unit and may be integral to that functional unit, such as shown for the DC-DC converter 111 which provides the power for functional unit 130 in order to drive device 132, and is contained within the unit 130. Yet further, the DC-DC converters may include a converter which provides a voltage supply for, and is specific to a functional unit but not integral with that unit; this is shown in figure 1 at the DC- DC converter 112, which is located adjacent to, but not integral with, functional unit 131 and provides power for a device 133. In contrast, figure 2 shows the battery pack in accordance with an embodiment of the present invention. The battery pack 203 includes lithium- ion battery 202 and incorporates either a multi-output DC-DC converter (not shown), or as shown in the figure, multiple separate DC-DC converters 210, 211 and 212. Each DC-DC converter outputs a separate constant output voltage. For instance, converter 210 may output a voltage of between 5 and 10V, and whereas converter 211 produces a constant output voltage, which is between 1 and 2.5 V and which is predetermined according to the functional units for which that voltage is required. In general, any particular converter 212, can supply a predetermined fixed output voltage of "N" volts. It should be noted that the arrangement shown includes three DC-DC converters; however an appropriate number of converters may be less than or greater than three, depending on the specific requirements of the portable device for which the battery pack is intended.

The individual DC-DC converters thus comprise secondary sources for different blocks in the portable device. The converters may operate in either up or down mode as appropriate. In particular, a converter which is capable of operating in either an up or a down at mode may be required to provide an output voltage at a particular predetermined voltage in a 5 to 10V range, since, during at least a partly discharged state of the battery, this voltage will exceed the direct voltage output from the battery: a buck-boost converter would be suitable for use in such a situation; in contrast, where the voltage is required within a 1 to 2.5 V range, a down converter will always be used, and either a buck converter or a buck-boost converter would be suitable for use in the situation. Suitable converter types include charge pumps (Integrated capacitor-based converters), or inductive DC-DC converters. Such DC-DC converters may conveniently be based on Passive Integrated Circuits (PICs) technology, such as is currently being development by NXP Semiconductors, and which can provide capacitors with suitably high spatial densities, for instance within the 100-300 nF/mm² range. This facilitates particularly space- efficient multiple output capacitive integrated charge pump DC-DC converters without the need for external components. Such multiple output DC-DC converters have very small dimensions and thus can be conveniently integrated into the battery pack. The individual converters 210, 211 and 212 are accessed and controlled by means of a serial interface 205. The serial interface 205 may be under the control of the portable device's microprocessor. For instance, in the case of a mobile phone, serial interface 205 may be under the control of the phone's CPU. The phone's CPU can determine which voltages are required in order to drive for instance, a display unit, a flash system, or an RF block, in dependence on which of these functional units are in demand, and communicate this information to the battery pack by means of the serial interface 205. Since in general, down-converters have higher efficiencies than up-converters, it will be appreciated that the system will use a down-converter, in preference to an up converter, where-ever appropriate.

Further, the skilled person will readily appreciate that it would be possible to supply a voltage of, say, 7.5V, to take an arbitrary voltage within the 5.0 - 8.4V range, using an efficient down-converter only when the battery is nearly fully charged; when the battery output falls to below 7.5V, an up- converter would be required. Thus the controller may serve the additional function of associating a particular output voltage (which would normally be tied to a specific output pin or output pad of the battery pack), with one of two DC-DC converters, depending on the charge state of the battery itself, thus performing dynamic allocation of the DC-DC converters.

Since some of the functional units of the portable device may require very accurately controlled current or voltage supplies, it is particularly helpful if each of the converters comprising the battery pack can be programmed to ensure either constant current or constant voltage, as well as remaining stable both in time and over the operating temperature range of the device. Some functional units in the portable device may require constant current. This is the case for instance for an LED flashlight functional unit. However since LEDs show very significant forward voltage variation, it is not possible to rely on a fixed voltage to provide a constant current to achieve the desired output in this case. So in the case of a flashlight it is preferable to use DC-DC converter which can provide a constant current. Conversely, other circuits such as TFT display drivers or RF amplifiers require a constant voltage.

In order to facilitate accurate measurement of the supplied voltage, each converter or some of the converters may have a V-sense or Kelvin contact. The data from the V-sense contact may be directed to the respective

DC-DC converter, or to the controller, or both. In such a way, feedback can be organized via the digital serial interface, or via an analog V-sense line.

Different embodiments may use either, or both or neither, of these two configurations of V-sense feedback.

A particular implementation of a battery pack as shown in figure 2 is illustrated in figure 3. Figure 3 shows a lithium-ion battery 302, which is contained within a battery pack 303. In addition to the lithium-ion battery 302, the battery pack includes a control unit 350 and several DC-DC converters - in the particular example shown in figure 3, there are three DC-DC converters 310, 311 and 312. Each DC-DC converter is under the control of control unit 350. An interface unit 340 provides communication means, for communication between the battery pack 303 and a portable device (not shown) for which the battery pack is intended. As shown, the communication means comprises a serial digital interface 360. The interface unit 340 also comprises the voltage outputs from the battery pack by means of individual output pins or pads. Interface unit 340 also includes V-sense or Kelvin probes, shown at 330, 321 and 332.

In operation, the control unit 350 controls the converters 310, 311 and

312 in dependence on control information provided through the communication means 360 from the portable device's microprocessor. Controller 350 may determine which of the converters 310, 311 and 31 to need be operational and which can be switched off; furthermore, in another embodiment, it may also be able to control the output voltage from any individual converter. Thus, the controller 350 may enable of the battery pack to be compatible with various portable devices, which require different voltage power supplies to each other, and to operate in constant current or constant voltage mode.

From the present disclosure it will be apparent that a battery pack, for use with portable of mobile devices, is disclosed which comprises an integral DC-DC converter in addition to the Li-ion battery. The DC-DC converter is capable of providing an output voltage which is higher than the direct output of the Lithium-ion battery. In a particularly preferred embodiment, the battery- pack further comprises at least one further DCDC converter to provide a second output voltage, which is different to the first output voltage.

From reading the present disclosure, other variations and modifications will be apparent to the skilled person. Such variations and modifications may involve equivalent and other features which are already known in the art of battery packs and which may be used instead of, or in addition to, features already described herein.

Although the appended claims are directed to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention.

Features which are described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

The applicant hereby gives notice that new claims may be formulated to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom. For the sake of completeness it is also stated that the term "comprising" does not exclude other elements or steps, the term "a" or "an" does not exclude a plurality, a single processor or other unit may fulfil the functions of several means recited in the claims and reference signs in the claims shall not be construed as limiting the scope of the claims.

Claims

1. A battery pack (303) for use with a portable device, the battery pack comprising

one or a plurality of lithium-ion cells (302) providing a first voltage, a DC-DC converter (310) operable under control of a control unit (350) and for converting the first voltage into a second voltage (320), an interface unit (340) for receiving, in use, information from the portable device and supplying information to the control unit,

the control unit (350) being for controlling the DC-DC converter in response to the interface unit (340),

wherein the DC-DC converter is adapted such that the second voltage can be greater than the first voltage.

2. A battery pack as claimed in claim 1 , further comprising at least one further DC-DC converter (311 , 312) operable under control of the control unit, for converting the first voltage into at least one further voltage (321 , 322) which is different from the second voltage.

3. A battery pack as claimed in claim 1 , wherein said DC-DC converter is a multi-output DC-DC converter adapted to further convert the first voltage into at least one further voltage which is different from the second voltage.

4. A battery pack as claimed in claim 2 or claim 3, wherein the controller controls the magnitude of at least one of the second voltage and the at least one further voltage.

5. A battery pack as claimed in any preceding claim, wherein said interface unit is a digital interface unit.

6. A battery pack as claimed in any preceding claim, wherein said interface unit further comprises at least one V-sense input for receiving voltage sense information from the portable device.