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Step-Down Dc-to-dc Converter with 60 V Transient Protection

Step-Down Dc-to-dc Converter with 60 V Transient Protection

Linear Technology Corporation announces the LT3667, a 400 mA, 40 V step-down switching regulator with dual LDO outputs packaged in a 3 mm x 5 mm QFN or MSOP-16E. The LT3667 offers a highly compact, triple output solution for automotive and industrial applications. The LT3667 operates from a VIN range of 4.3 V to 40 V with transient protection to 60 V, making it ideal for load-dump and cold-crank conditions found in automotive applications. Its internal 600 mA internal switch delivers up to 400 mA, which is distributed to the combined loads of the primary output and both of the LDOs. The primary switching channel delivers outputs as low as 1.2 V, whereas each LDO can deliver outputs as low as 0.8 V. For example, a common application will have the switcher delivering 200 mA at 5 V, with one LDO delivering 100 mA at 2.5 V and the second delivering 100 mA at 1.8 V.

The LT3667 requires only 50 µA of quiescent current when all three channels are in regulation, making it ideal for always-on automotive applications. The LT3667's switching frequency is user programmable from 250 kHz to 2.2 MHz, enabling the designer to optimize efficiency while avoiding critical noise-sensitive frequency bands. Each integrated LDO has an accurate programmable current limit up to 200 mA, offering an additional level of reliability. Although the LDOs can be powered by independent inputs, powering them from the primary switching output ensures both high efficiency and low noise. The combination of its 3 mm x 5 mm QFN-24 package (or thermally enhanced MSOP-16E) and high switching frequency, which keeps external capacitors and inductor small, provides a compact, thermally efficient footprint.

The LT3667's main switcher utilizes a high efficiency 600mA switch with the necessary oscillator, control, logic circuitry and LDOs integrated into a single die. Special design techniques enable high efficiency over a wide input voltage range while its current-mode topology enables fast transient response and excellent loop stability. Other features include power indicators, synchronization capability, reverse-battery protection, current and thermal limiting and programmable undervoltage lockout.

The LT3667EUDD is offered in a 3 mm x 5 mm 24-lead QFN package, and the LT3667EMSE is offered in a thermally enhanced 16-lead MSOP package. Both are priced at $2.55 each. The LT3667IUDD and the LT3667IMSE are tested and guaranteed to operate from -40 °C to 125 °C operating junction temperature and are both priced at $2.81 each. A high temperature version, the LT3667HUDD, is tested and guaranteed to operate from -40 °C to 150 °C operating junction temperature, priced at $3.06 each. All prices are for 1,000-piece quantities and all versions of the LT3667 are available from stock.


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