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EETE JULAUG 2012

DESIGN & PRODUCTS POwER SUPPlIES instrumentation low noise bias generators, portable medical equipment and automotive infotainment systems. The LTC3260 is available in a low-profile (0.75mm) 3x4mm 14-lead DFN package and a 16-lead mSOp package, both with a backside thermal pad. The LTc3261 is available in a 12-lead mSOp package with backside thermal pad. Operating junction temperature for either device is -40°c to +125°c. Low output ripple The LTc3260’s design inherently provides low noise perfor- mance. The device’s high operating frequency leads to a low output ripple. The LTc3260 LDOs further reject this ripple as shown in Figure 3 to deliver very low noise outputs <1mVp-p Fig. 1. LTC3260 application circuit. that are ideal for noise sensitive applications such as opera- tional amplifiers and ADC drivers. Protection circuitry The LTc3260 has built-in short-circuit current limit as well as over temperature protection. During a short-circuit condition, the part automatically limits its output current to approximately 160mA. If the junction temperature exceeds approximately 175°C the thermal shutdown circuitry disables current delivery to the output. Once the junction temperature drops back to approximately 165°c current delivery to the output is resumed. When thermal protection is active the junction temperature is beyond the specified operating range. Thermal protection is intended for momentary overload conditions outside normal operation. Continuous operation above the specified maximum Fig. 2. LTC3261 application circuit. operating junction temperature may impair device reliability. Any solution to satisfy the charge pump Ic design con- Conclusion straints outlined above would combine an efficient high voltage The charge pump in some ways has been nearly forgotten due charge pump with regulated outputs and low output noise. to limited voltage range and historical performance that placed it somewhere in between an LDO and a switching regulator. For- A new and simple solution tunately, the high voltage LTc3260 and LTc3261 charge pumps Linear Technology has developed simple, yet sophisticated, address these needs. The 150mA LTC3260 offers a number high voltage inverting monolithic charge pump Ics for these of useful features in a small footprint, reducing overall solution applications. The LTc3260 and LTc3261 are versatile charge size and in turn enabling more compact, simpler designs. The pumps. The LTc3261 is a high voltage inverting charge pump LTc3261 is a subset of the LTc3260 and provides a 100mA that can deliver up to 100mA of output current. Whereas the high voltage inverted output. So, for those designers who do LTc3260 includes an inverting charge pump plus both positive not like to use inductors, there are simple, high voltage charge and negative LDO regulators that can source up to 50mA output pumps to be used instead. current each with low dropout voltage operation. The negative LDO post regulator is powered from the inverting charge pump output. The positive and negative LDO output voltages can be adjusted down to 1.2V and -1.2V, respectively, using external resistor dividers. Both devices operate over a wide 4.5V to 32V input voltage range. See figures 1 and 2 for details. The internal charge pump of both the LTc3260 and LTc3261 functions in either low quiescent current Burst mode operation or low noise constant frequency mode at up to 88% efficiency. In Burst mode operation, the charge pump output regulates to –0.94 • VIN. Also, in Burst mode operation, the LTc3261 draws only 60μA of quiescent current, while the LTC3260 draws only 100uA with both LDOs enabled. constant frequency opera- tion offers low input and output ripple; in this mode the charge pump produces an output equal to –VIN and operates at a fixed 500khz or to a programmed value between 50khz to 500khz, using an external resistor. Other Ic features include low ex- ternal parts count with ceramic capacitor stability, soft-start circuitry to prevent excessive current flow during startup, plus short circuit and thermal protection. The LTc3260 and LTc3261 are well-suited for a variety of applications such as low noise Fig. 3. LTC3260 low output ripple performance. bipolar/inverting supplies from a high voltage input, industrial/ 18 Electronic Engineering Times Europe July/August 2012 www.electronics-eetimes.com


EETE JULAUG 2012
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