Patent Application
20130293185
1. Field
The present disclosure relates generally to communication systems, and more particularly, to high current battery charging using IR dropout compensation.
2. Background
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communications with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA), 3GPP Long Term Evolution (LTE) systems, and orthogonal frequency division multiple access (OFDMA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out, multiple-in-single-out or a multiple-in-multiple-out (MIMO) system.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, where NS
A MIMO system may support time division duplex (TDD) and/or frequency division duplex (FDD) systems. In a TDD system, the forward and reverse link transmissions are on the same frequency region so that the reciprocity principle allows the estimation of the forward link channel from the reverse link channel. This enables the base station to extract transmit beamforming gain on the forward link when the multiple antennas are available at the base station. In an FDD system, forward and reverse link transmissions are on different frequency regions.
As mobile devices have begun to perform more functions, the need for battery power becomes more important and the ability to charge a battery also become much more important. Most mobile devices manufactured today rely on lithium-ion batteries for power.
Lithium-ion batteries commonly require a constant current, constant voltage charging algorithm. A lithium-ion battery should be charged at a set current level (typically from 1 to 1.5 amperes) until it reaches its final voltage. At this point, the charger circuitry should switch over to constant voltage mode and provide the current necessary to hold the battery at this final voltage (typically at 4.2 V per cell). The charger must be capable of providing stable control loops for maintaining either current or voltage at a constant value, depending on the state of the battery. There is a need in the art for a method and apparatus for charging to a battery's full capacity without overcharging.
An embodiment provides a method for high current battery charging using IR dropout compensation. The method comprises the steps of measuring a battery current value; multiplying the battery current value by an effective resistance of the battery to produce an effective dropout voltage value; comparing the effective battery voltage value with a desired battery top off voltage value; adjusting a switch mode battery charger output setpoint based on a setpoint voltage; comparing the battery current with the terminal current; and terminating charging if the battery current is less than the terminal current, and measuring the battery current value again if the battery current is greater than the terminal current.
An additional embodiment provides a further method for charging a lithium-ion battery. This embodiment senses a battery voltage using a Kelvin sense at positive and negative terminals of the battery and then comparing the sensed battery voltage value with a desired battery top off voltage value. Charging is terminated if the battery voltage exceeds the desired battery top of voltage and continues if the battery voltage does not exceed the desired battery top of value.
A further embodiment provides an apparatus for high current battery charging using IR dropout compensation. The apparatus includes a battery field effect transistor, a switch mode battery charger; a comparator, a battery management system, a multiplier; and a processor for performing the required computations.
Yet a further embodiment provides an apparatus for charging a lithium-ion battery. The apparatus includes: means for measuring a battery current value; means for multiplying the battery current value by an effective resistance of the battery to produce an effective dropout voltage value; means for comparing the effective battery voltage value with a desired battery top off voltage value; means for adjusting a switch mode battery charger output setpoint based on a setpoint voltage; means for comparing battery current and terminal current; and means for terminating charging if the battery current is less than the terminal current; and means for measuring the battery current value again if the battery current is greater than the terminal current.
Yet a further embodiment provides an apparatus for charging a lithium-ion battery. The apparatus includes means for sensing a battery voltage using a Kelvin sense at both positive and negative terminals of the battery; means for comparing the sensed battery voltage value with a desired battery top off voltage value; and means for terminating charging if the battery voltage exceeds the desired battery top of value; and means for continuing charging if the battery voltage does not exceed the desired battery top of value.
A still further embodiment provides a non-transitory computer-readable medium containing instructions for causing a processor to perform the steps of: measuring a battery current value; multiplying the battery current value by an effective resistance of the battery to output an effective dropout voltage value. The processor then directs a comparison of the effective resistance of the battery voltage value with a desired battery top off voltage value. The switch mode battery charger output setpoint is adjusted based on a setpoint voltage. The battery current and terminal current are then compared and charging is terminated if the battery current is less than the terminal current, and continues if the battery current is greater than the terminal current.
An additional embodiment provides a non-transitory computer-readable medium containing instructions for causing a processor to perform the steps of: sensing a battery voltage via a desired Kelvin sense at both the positive and negative terminals of the battery. Next, the processor directs a comparison of the sensed battery voltage value with a desired battery top off voltage value. Charging is terminated if the battery voltage exceeds the desired battery top off value and continues if the battery voltage does not exceed the desired battery top off value.
Various aspects are now described with reference to the drawings. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects. It may be evident, however, that such aspect(s) may be practiced without these specific details.
As used in this application, the terms “component,” “module,” “system” and the like are intended to include a computer-related entity, such as, but not limited to hardware, firmware, a combination of hardware and software, software, or software in execution. For example, a component may be, but is not limited to being, a process running on a processor, a processor, an object, an executable, a thread of execution, a program and/or a computer. By way of illustration, both an application running on a computing device and the computing device can be a component. One or more components can reside within a process and/or thread of execution and a component may be localized on one computer and/or distributed between two or more computers. In addition, these components can execute from various computer readable media having various data structures stored thereon. The components may communicate by way of local and/or remote processes such as in accordance with a signal having one or more data packets, such as data from one component interacting with another component in a local system, distributed system, and/or across a network such as the Internet with other systems by way of the signal.
Furthermore, various aspects are described herein in connection with a terminal, which can be a wired terminal or a wireless terminal A terminal can also be called a system, device, subscriber unit, subscriber station, mobile station, mobile, mobile device, remote station, remote terminal, access terminal, user terminal, communication device, user agent, user device, or user equipment (UE). A wireless terminal may be a cellular telephone, a satellite phone, a cordless telephone, a Session Initiation Protocol (SIP) phone, a wireless local loop (WLL) station, a personal digital assistant (PDA), a handheld device having wireless connection capability, a computing device, or other processing devices connected to a wireless modem. Moreover, various aspects are described herein in connection with a base station. A base station may be utilized for communicating with wireless terminal(s) and may also be referred to as an access point, a Node B, or some other terminology.
Moreover, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” That is, unless specified otherwise, or clear from the context, the phrase “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, the phrase “X employs A or B” is satisfied by any of the following instances: X employs A; X employs B; or X employs both A and B. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from the context to be directed to a singular form.
The techniques described herein may be used for various wireless communication networks such as Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, Single-Carrier FDMA (SC-FDMA) networks, etc. The terms “networks” and “systems” are often used interchangeably. A CDMA network may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), CDMA2000, etc. UTRA includes Wideband CDMA (W-CDMA). CDMA2000 covers IS-2000, IS-95 and technology such as Global System for Mobile Communication (GSM).
An OFDMA network may implement a radio technology such as Evolved UTRA (E-UTRA), the Institute of Electrical and Electronics Engineers (IEEE) 802.11, IEEE 802.16, IEEE 802.20, Flash-OFDAM®, etc. UTRA, E-UTRA, and GSM are part of Universal Mobile Telecommunication System (UMTS). Long Term Evolution (LTE) is a release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS, and LTE are described in documents from an organization named “3rd Generation Partnership Project” (3GPP). CDMA2000 is described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). These various radio technologies and standards are known in the art. For clarity, certain aspects of the techniques are described below for LTE, and LTE terminology is used in much of the description below. It should be noted that the LTE terminology is used by way of illustration and the scope of the disclosure is not limited to LTE. Rather, the techniques described herein may be utilized in various application involving wireless transmissions, such as personal area networks (PANs), body area networks (BANs), location, Bluetooth, GPS, UWB, RFID, and the like. Further, the techniques may also be utilized in wired systems, such as cable modems, fiber-based systems, and the like.
Single carrier frequency division multiple access (SC-FDMA), which utilizes single carrier modulation and frequency domain equalization has similar performance and essentially the same overall complexity as those of an OFDMA system. SC-FDMA signal may have lower peak-to-average power ration (PAPR) because of its inherent single carrier structure. SC-FDMA may be used in the uplink communications where the lower PAPR greatly benefits the mobile terminal in terms of transmit power efficiency.
Each group of antennas and/or the area in which they are designed to communicate is often referred to as a sector of the access point. In an aspect, antenna groups each are designed to communicate to access terminals in a sector of the areas covered by access point 102.
In communication over downlinks or forward links 118 and 124, the transmitting antennas of access point utilize beamforming in order to improve the signal-to-noise ratio (SNR) of downlinks or forward links for the different access terminals 116 and 122. Also, an access point using beamforming to transmit to access terminals scattered randomly through its coverage causes less interference to access terminals in neighboring cells than an access point transmitting through a single antenna to all its access terminals.
An access point may be a fixed station used for communicating with the terminals and may also be referred to as a Node B, an evolved Node B (eNB), or some other terminology. An access terminal may also be called a mobile station, user equipment (UE), a wireless communication device, terminal, or some other terminology. For certain aspects, either the AP 102, or the access terminals 116, 122 may utilize the proposed transmit echo cancellation technique to improve performance of the system.
In an aspect, each data stream is transmitted over a respective transmit antenna. TX data processor 214 formats, codes, and interleaves the traffic data for each data stream based on a particular coding scheme selected for that data stream to provided coded data.
The coded data for each data stream may be multiplexed with pilot data using OFDM techniques. The pilot data is typically a known data pattern that is processed in a known manner and may be used at the receiver system to estimate the channel response. The multiplexed pilot and coded data for each data stream is then modulated (e.g., symbol mapped) based on a particular based on a particular modulation scheme (e.g. a Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), M-PSK in which M may be a power of two, or M-QAM, (Quadrature Amplitude Modulation)) selected for that data stream to provide modulation symbols. The data rate, coding, and modulation for each data stream may be determined by instructions performed by processor 230 that may be coupled with a memory 232.
The modulation symbols for all data streams are then provided to a TX MIMO processor 220, which may further process the modulation symbols (e.g., for OFDM). TX MIMO processor 220 then provides NT modulation symbol streams to NT transmitters (TMTR) 222a through 222t. In certain aspects TX MIMO processor 220 applies beamforming weights to the symbols of the data streams and to the antenna from which the symbol is being transmitted.
Each transmitter 222 receives and processes a respective symbol stream to provide one or more analog signals, and further conditions (e.g., amplifies, filters, and upconverts) the analog signals to provide a modulated signal suitable for transmission over the MIMO channel. NT modulated signals from transmitters 222a through 222t are then transmitted from NT antennas 224a through 224t, respectively.
At receiver system 250, the transmitted modulated signals are received by the NR antennas 252a through 252r and the received signal from each antenna 252 is provided to a respective receiver (RCVR) 254a through 254r. each receiver 254 conditions (e.g., filters, amplifies, and downconverts) a respective received signal, digitizes the conditioned signal to provide samples, and further processes the samples to provide a corresponding “received” symbol stream.
A RX data processor 260 then receives and processes the NR received symbol streams from NR receivers 254 based on a particular receiver processing technique to provide NT “detected” symbol streams. The RX data processor 260 then demodulates, deinterleaves, and decodes each detected symbol stream to recover the traffic data for the data stream. The processing by RX processor 260 is complementary to that performed by TX MIMO processor 220 and TX data processor 214 at transmitter system 210.
Processor 270, coupled to memory 272, formulates a reverse link message. The reverse link message may comprise various types of information regarding the communication link and/or the received data stream. The reverse link message is then processed by a TX data processor 238, which also receives traffic data for a number of data streams for ma data source 236, modulated by a modulator 280, conditioned by transmitters 254a through 254r, and transmitted back to transmitter system 210.
At transmitter system 210, the modulated signals from receiver system 250 are received by antennas 224, conditioned by receivers 222, demodulated by a demodulator 240 and processed by a RX data processor 242 to extract the reserve link message transmitted by the receiver system 250.
The operations of the mobile device described above require sufficient battery power to perform the functions. Most mobile devices utilize lithium-ion batteries. Lithium-ion batteries require a constant current, constant voltage charging algorithm. A lithium-ion battery should be charged at a set current level, which is typically from 1 to 1.5 amperes until the battery reaches its final voltage. Once the final voltage is reached, the charger circuitry should switch over to constant voltage mode and provide the current necessary to maintain the battery at this final voltage. The final voltage is typically 4.2 V per cell. The charger must be capable of providing stable control loops to maintain either current or voltage at a constant value, depending on the state of the battery.
The challenge in charging a lithium-ion battery is to achieve the battery's full capacity without overcharging it. Overcharging may result in a catastrophic failure. There is little room for error as lithium-ion batteries have a ±1% margin. Overcharging by more than 1% could result in battery failure, while undercharging by more than 1% results in reduced capacity. Since the margin for error is so small, high accuracy is required from the charging control circuitry. In order to achieve this accuracy, the controller must have a precision voltage reference, a low-offset high gain feedback amplifier, and an accurately matched resistance divider. The combined errors of all these components must result in an overall error less than ±1%.
Battery voltage is not being measured correctly because of the printed wiring board (PWB), battery field effect transistor (BATFET), and the sensing line resistance (RSense) losses cause the measured voltage to be higher than it actually is at the battery terminals. This causes slower charging since the transition from constant current to constant voltage charging mode will occur earlier than desired. This is particularly true for two wire and three wire measuring systems. All two wire and three wire measuring systems are subject to measurement errors due to current voltage (IR) drop in the sense wires to a device. This occurs regardless of whether resistance, voltage, or current is being measured. A four wire system offers the ability to remove all effects of IR drop. In a four wire measurement system two sense lines, one on either side of the component being measured, are connected to a very high impedance (>10M ohms) inputs of the measuring device. This very high impedance input limits the current flow or IR drop to below micro-volts in the sense lines. This four wire measurement approach using very high impedance sense lines is known as a Kelvin sense measurement.
Charging is accomplished through charger port 302, which may be either a universal serial bus input or a DC input port. This charger port 302 provides a current voltage source. Charger port 302 is connected to switch mode battery charger (SMBC) 304 located internally in power management chip 324. SMBC 304 utilizes a voltage set point. The SMBC 304 is connected to the charger port 302 and also to the LC power line filter 322. Once charging reaches the voltage set point in the SMBC, the current is dropped to a trickle charge level. The SMBC voltage set point is calculated using the following formula:
4.2v+Ibat(measured)×Reff(calculated)=Vset
In a power management chip 324 using present technology, due to the printed wiring board resistance adjusting the SMBC voltage set point, setting the voltage set point higher provides only a limited, improvement for a 47 miliohm Reff and a 2 amp battery charging current. In an embodiment, a 50% reduction in total charging time by remaining in charge current mode longer. This is in contrast to other methods which lengthen the time spent in the charge current mode and the inefficient time spent with SMBC output voltage greater than the charging termination voltage .
The SMBC LC filter 322 is also connected to the BATFET 306. BATFET 306 is in turn connected to battery 308. SMBC 304 provides an input to comparator 320. The SMBC's output is fed back into the error comparator 320.
Currently flowing through the battery also flows through Rsense 310 which develops a voltage (Ibat x Rsense) across Rsense 310 which is corrected to and measured by a high impedance amplifier 312. This value represents Ibat. Ibat is then multiplied by Reff 316 to represent the estimated Ibatt x Reffdrop seen by the system. This is compared to the desired battery voltage setpoint in comparator 318. This produces an error to be used by error comparator 320 to control the SMBC output voltage setpoint. Thus there are two loops here: an inner loop from SMBC 304, LC power line filter 322, comparator 320, to an outer loop from SMBC 304, LC filter 322, BATFET 306, battery 308, Rsense resistor 310, Rsense amplifier 312, xReff 316, high level operating system 314, software comparator 318, and comparator 320.
SMBC Vout Setpoint=4.2v+Ibat*Reff
The embodiment depicted in
It is understood that the specific order or hierarchy of steps in the processes disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented.
The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the term “some” refers to one or more. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed as a means plus function unless the element is expressly recited using the phrase “means for.”
