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Power mgmt chip maximises battery runtime

Posted: 18 Jan 2008     Print Version  Bookmark and Share

Keywords:buck-boost regulator  Lithium battery  I2C control 

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Linear Technology Corp. has announced the LTC3556, the latest in a family of smaller next-generation, multi-function power management solutions for Li-Ion/Polymer battery applications. The LTC3556 integrates a switching PowerPath manager, a stand-alone battery charger, a diode, I2C control, a synchronous buck-boost regulator, two high efficiency synchronous buck regulators and an always-on LDO, all in a compact, low-profile 4-by-5mm QFN package.

The LTC3556's PowerPath control feature seamlessly manages power flow between multiple input sources such as a wall adapter or USB port and the Lithium battery while preferentially providing power to the system load. In addition, its "instant-ON" operation ensures system load power even with a dead or missing battery. For fast charging, the LTC3556's switching input stage converts nearly all of the 2.5W available from the USB port to charging current, enabling up to 700mA from a 500mA limited USB supply or up to 1.5A when wall powered.

An internal 180milliohm ideal diode plus optional external ideal diode controller provide a low loss power path, further minimising heat generation and maximising efficiency. The LTC3556's onboard synchronous buck-boost regulator can deliver up to 1A continuously and is suitable for efficiently regulating a 3.3V output voltage over the full Lithium battery voltage range, down to 2.75V input. The LTC3556's two integrated synchronous buck regulators feature 100 per cent duty cycle operation and are capable of delivering output currents of 400mA each, with adjustable output voltages down to 0.8V.

The LTC3556 switching regulator's internal low RDS(ON) switches enable efficiency as high as 94 per cent, maximising battery run time. In addition, Burst Mode operation optimises efficiency at light loads with a quiescent current of only 20µA for the buck-boost regulator and only 35µA for each buck regulator ( < 1µA each in shutdown for all). The high 2.25MHz switching frequency allows the use of tiny low cost capacitors and inductors less than 1mm in height. Furthermore, the regulators are stable with ceramic output capacitors, achieving very low output voltage ripple.

The LTC3556 features USB-compatible programmable current limiting to 100mA/500mA/1A, while its Bat-Track adaptive output control enables high efficiency battery charging and reduces power dissipation. Stand-alone autonomous operation simplifies design, eliminating the need for an external microprocessor for battery charge termination. To preserve battery energy, the LTC3556 draws only 44µA in suspend mode. The charger is compatible with inputs up to 5.5V (7V absolute maximum transient for added robustness).

The LTC3556 is available from stock in a compact, low-profile (0.75mm) 4-by-5mm QFN-28 package. Pricing starts at Rs.189.50 ($4.80) each for 1,000-piece quantities.

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