Advances in low power electronics now allow placementof bATtery-powered sensors and other devices in locationsfar from the power grid. Ideally, for true grid independence,the batteries should not need replacement, but instead berecharged using locally available renewable energy, suchas solar power. This Design Note shows how to producea compact bATtery charger that operates from a small2-cell solar panel. A unique feature of this design is thatthe DC/DC converter uses power point control to extractmaximum power from the solar panel.
The LTC®4155 and LTC4156 are dual multiplexed-inputbATtery chargers with PowerPath™ control, featuring I2Cprogrammability and USB On-The-Go for systems suchas tablet PCs and other high power density applications.The LTC4155’s float voltage (VFLOAT) range is optimizedfor Li-Ion batteries, while the LTC4156 is optimized forlithium iron phosphate (LiFePO4)batteries, supportingsystem loads to 4A with up to 3.5A of bATtery chargecurrent. I2C controls a broad range of functions and USBOn-The-Go functionality is controlled directly from theUSB connector ID pin.
Handheld electronic devices play a key role in our everydaylives. Because dependability is paramount, handhelds arecarefully engineered with lightweight power sources forreliable use under normal conditions. But no amount ofcareful engineering can prevent the mistreatment theywill undergo at the hands of humans. For example, whathappens when a factory worker drops a bar code scanner,causing the bATtery to pop out? Such events areelectronically unpredictable, and important data storedin volatile memory would be lost without some form ofsafety net—namely a short-term power holdup systemthat stores suffi cient energy to supply standby power untilthe bATtery can be replaced or the data can be stored inpermanent memory.
The LTC®4099 high effi ciency USB power manager andLi-Ion/Polymer bATtery charger seamlessly managespower distribution from multiple sources in portableapplications. It is differentiated from other USB powermanagers by its bidirectional I2C port that allows the hostmicroprocessor to control and monitor all aspects of theUSB power management and bATtery charging processes.In addition, a programmable interrupt generation functionalerts the host microprocessor to changes in device statusand provides unprecedented control of power managementfunctions. This high degree of confi gurability allowspost-layout changes in operation, even changes in thefi eld, and it allows a single qualifi ed device to be usedin a variety of products, thus reducing design time andeasing inventory management.
Notebook and palmtop systems need a multiplicity ofregulated voltages developed from a single bATtery. Smallsize, light weight, and high efficiency are mandatory forcompetitive solutions in this area. Small increases inefficiency extend bATtery life, making the final productmuch more usable with no increase in weight. Additionally,high efficiency minimizes the heat sinks needed onthe power regulating components, further reducing systemweight and size.
In an increasing trend, telecommunications, networking,audio and instrumentation require low noise power supplies.In particular, there is interest in low noise, lowdropout linear regulators (LDO). These components powernoise-sensitive circuitry, circuitry that contains noisesensitiveelements or both. Additionally, to conserve power,particularly in bATtery driven apparatus such as cellulartelephones, the regulators must operate with low input-tooutputvoltages.1 Devices presently becoming availablemeet these requirements (see separate section, “A Familyof 20mVRMS Noise, Low Dropout Regulators”).
For a variety of reasons, it is desirable to charge batteriesas rapidly as possible. At the same time, overchargingmust be limited to prolong bATtery life. Such limitation ofovercharging depends on factors such as the choice ofcharge termination technique and the use of multi-rate/multi-stage charging schemes. The majority of bATterycharger ICs available today lock the user into one fixedcharging regimen, with at best a limited number ofcustomization options to suit a variety of application needsor bATtery types. The LTC®1325 addresses these shortcomingsby providing the user with all the functionalblocks needed to implement a simple but highly flexiblebATtery charger (see Figure 1) which not only addressesthe issue of charging batteries but also those of bATteryconditioning and capacity monitoring.
The design of bATtery-powered equipment can often bequite challenging. Since few ICs can operate directly fromthe end-of-life voltage from a 2-cell bATtery (about 1.8V),most systems require a DC/DCconverter. The systemdesigner often has a limited area in which to place the DC/DC converter; associated inductors and capacitors must be
Portable, bATtery-powered operation of electronic apparatushas become increasingly desirable. Medical, remotedata acquisition, power monitoring and other applicationsare good candidates for bATteryoperation. In some circumstances,due to space, power or reliability considerations,it is preferable to operate the circuitry from a single 1.5Vcell. Unfortunately, a 1.5V supply eliminates almost alllinear ICs as design candidates. In fact, the LM10 opamp-reference and the LT®1017/LT1018 comparators arethe only IC gain blocks fully specifi ed for 1.5V operation.Further complications are presented by the 600mV dropof silicon transistors and diodes. This limitation consumesa substantial portion of available supply range, makingcircuit design diffi cult. Additionally, any circuit designedfor 1.5V operation mustfunction at end-of-life bATteryvoltage, typically 1.3V. (See Box Section, “Componentsfor 1.5V Operation.”)
