Project Analog - December 2007 - (Page 20)

mcP73837/38 • High Accuracy Preset Voltage Regulation: ±0.5% • Four Voltage Regulation Options • Fully Integrated Linear Charge Management Controller: • Autonomous Power Source Selection • Constant Current (CC) / Constant Voltage (CV) Operation with Thermal Regulation • Selectable USB-Port Charge Current • Programmable AC-Adapter Charge Current • Two Charge Status Outputs • Power-Good Monitor: MCP73837 • Timer Enable: MCP73838 • Automatic Recharge: • Automatic End-of-Charge Control: – Selectable Charge Termination Current Ratio – Selectable Safety Timer Period • Preconditioning of Deeply Depleted Cells • Battery Cell Temperature Monitor • UVLO (Undervoltage Lockout) • Low-Dropout (LDO) Linear Regulator Mode click here for more information about the MCP73837/38. circuitry and a lower voltage of 2V is best suited for digital activities. The adjustable power-converter in Figure 1 has high efficiency with lowoutput currents and Li-Ion battery input voltages (4.2V down to 2.8V). For these reasons, this circuit uses a regulated, adjustable charge pump, DC/DC converter (MCP1252-ADJ). Controlling the power-supply voltage for various operations is only half of the story. If you really have a lower power “state of mind”, you will want to power down some parts of the microcontroller while letting other sections continue to operate. As an example, you can independently run an A/D or D/A conversion or the USART communication interface from the microcontroller. These device functions may only need power locally. Optimizing the external-peripheral power trade offs is also important. In addition, you will find real power savings when using the external and internal peripherals in concert with the microcontrollers programming capability. For instance, the microcontroller controls the power-supply volt- you can accomplish an improvement in power consumption, and consequently an increase in functionality if you understand the hardware options and the tools available in microcontrollers. age by switching a new configuration into the resistive feedback system of the MCP1252-ADJ regulated, adjustable-output charge pump. The charge pump generates a higher output voltage to insure that the analog circuitry performs at its optimum level. Digital events from the microcontroller can tolerate a lower power-supply voltage. For instance, the power-supply specifications of the PIC18F1320 are from 2V to 5.5V. You can calculate the power savings for this type of change as a direct ratio of the two voltages from the charge pump. Power savings are further improved if the external peripherals are powered down with the lower-power supply voltage using the I/O ports. concLuSIon Device power savings in batterypowered applications are extremely important. You can achieve true value by using the microcontroller’s programmability. You can do this by changing the power-supply voltage at the output of a regulated charge pump. A second area would be to power down non-critical peripherals when not in use. The combination of lower-power peripherals and microcontroller modes enhances your changes of having a low-power, battery-powered solution. Contents Viewpoint Charging lithium-ion batteries New trends in battery-powered portable devices Low power design: LDO thermal considerations Analog news • Microchip analog page Battery charger overview Sample center microchipDIRECT Reference designs/ app notes Technical training 20 · prOject AnALOg · Dec 07 http://www.microchip.com http://www.microchip.com/analog http://www.microchip.com/analog http://www.microchip.com/batterychargers http://www.microchip.com/batterychargers http://sample.microchip.com/Default.aspx?testCookies=true http://www.microchipdirect.com/catalogselection.aspx?returnURL=default.aspx http://ww1.microchip.com/downloads/en/DeviceDoc/22071a.pdf http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1469&filter1=function&redirects=appnotes http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1469&filter1=function&redirects=appnotes http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1423

Table of Contents Feed for the Digital Edition of Project Analog - December 2007

Project Analog - December 2007 Contents Viewpoint About Project Analog Sponsor4 Charging Lithium-Ion Batteries: System Considerations New Trends In Battery-Powered Portable Devices Low Power Design: LDO Thermal Considerations Runtime Measurements for a Hybrid Power Source Battery-Powered System Design Considerations Analog News—Analog News from Multiple Sources Enter to Win an iPhone Contact Project Analog Sponsor Mindi™ Battery & Power Circuit Simulator Microchip Advanced Parts Selector (MAPS)

Project Analog - December 2007

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