This application note features 8-, 10-, and 12-bit dataacquisition components in various circuit configurations.The circuits include bATtery monitoring, temperature sensing,isolated serial interfaces, and microprocessor andmicrocontroller serial and parallel interfaces. Also includedare voltage reference circuits (Application Note 42contains more voltage reference circuits).
Low power operation of electronic apparatus has becomeincreasingly desirable. Medical, remote data acquisition,power monitoring and other applications are good candidatesfor bATtery driven, low power operation. Micropoweranalog circuits for transducer-based signal conditioningpresent a special class of problems. Although micropowerICs are available, the interconnection of these devices toform a functioning micropower circuit requires care. (SeeBox Sections, “Some Guidelines for Micropower Designand an Example” and “Parasitic Effects of Test Equipmenton Micropower Circuits.”) In particular, trade-offs betweensignal levels and power dissipation become painful whenperformance in the 10-bit to 12-bit area is desirable.
Portable, bATtery-powered operation of electronic apparatushas become increasingly desirable. Medical, remotedata acquisition, power monitoring and other applicationsare good candidates for bATtery operation. 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 must function at end-of-life bATteryvoltage, typically 1.3V. (See Box Section, “Componentsfor 1.5V Operation.”)
The LTP5900 includes sufficient power supply filtering and decoupling capacitancesuch that additional filtering should not be necessary for most bATtery-powereddesigns. Care must be taken to avoid large transient voltages on the supply as theM2510 steps up its current consumption (see the section on Supply Design below).
Linear Technology’s high performance bATtery management ICsenable long bATtery life and run time, while providing precision charging control, constantstatus monitoring and stringent bATtery protection. Our proprietary design techniques seamlesslymanage multiple input sources while providing small solution footprints, faster charging and100% standalone operation. bATtery and circuit protection features enable improved thermalperformance and high reliability operation.
Abstract: It is critically important that lithium-ion bATtery stacks have a good bATtery-management system for monitoring many cellvoltages and cell temperatures. Without that monitoring, thermal runaway can lead to a bATtery explosion. This design idea presentsa low-power circuit that measures the temperature of up to 12 thermistors. It powers and configures the multiplexers, and also putsthe muxes into shutdown to save power when not measuring temperatures.
Smart Batteries are an increasingly popular choice formore than just traditional compact consumer electronicdevices. For example, Smart Batteries are being used asbATtery backup for products such as blade servers, whereknowing bATtery status is very important
Linear Technology offers a variety of devices that simplifyconverting power from a USB cable, but the LTC®3455represents the highest level of functional integration yet. The LTC3455 seamlessly manages power flowbetween an AC adapter, USB cable and Li-ion bATtery,while complying with USB power standards, all from a4mm × 4mm QFN package. In addtion, two high efficiencysynchronous buck converters generate low voltage railswhich most USB-powered peripherals require. TheLTC3455 also provides power-on reset signals for themicroprocessor, a Hot SwapTM output for poweringmemory cards as well as an uncommitted gain blocksuitable for use as a low-bATtery comparator or an LDOcontroller. The PCB real estate required for the entire USBpower control circuit and two DC/DC converters is only225mm2.
