42-V, 750-mA, 2.2-MHz step-down dc/dc converter only requires 2.5-uA quiescent current

October 26, 2011 // By Paul Buckley
Linear Technology Corporation has unveiled a 750 mA, 42 V step-down switching regulator with integrated boost and catch diodes. Its Burst Mode operation keeps quiescent current under 2.5 µA in no load standby conditions. The LT3973's 4.2 V to 42 V input voltage range makes it ideal for automotive and industrial applications. Its internal 1.2 A switch can deliver up to 750 mA of continuous output current to voltages as low as 1.21 V.

The device's Burst Mode operation offers ultralow quiescent current, making it well suited for applications such as automotive or industrial systems, which demand always-on operation and optimum battery life.     

The design of the LT3973 maintains a minimum dropout voltage of 530 mV when the output voltage drops below the programmed output voltage, ideal for applications subjected to scenarios such as automotive cold-crank. Switching frequency is user programmable from 200 kHz to 2.2 MHz, enabling the designer to optimize efficiency while avoiding critical noise-sensitive frequency bands. The combination of its 10-lead 3 mm x 3 mm DFN-10 (or thermally enhanced MSOP) package and high switching frequency keeps external inductors and capacitors small, providing a compact, thermally efficient footprint.     

The LT3973 utilizes a high efficiency 250 mV CESAT switch, with the necessary boost and catch diodes, oscillator, control and logic circuitry integrated into a single die. Low ripple Burst Mode operation maintains high efficiency at low output currents while keeping output ripple below 10 mV PK-PK . Special design techniques and a new high voltage process enable high efficiency over a wide input voltage range, and the LT3973's current mode topology enables fast transient response and excellent loop stability. Other features include a power good flag, internal catch diode current limit and thermal protection.     


The LT3973EDD is packaged in a 3mm x 3mm DFN-10, and the LT3973EMSE is in a thermally enhanced MSOP-10, priced starting at $2.75 and $2.85 each, respectively for 1,000 piece quantities.

The LT3973IDD and LT3973IMSE are tested and guaranteed to operate from a -40 to 125°C operating junction temperature and are priced at $3.03 and $3.14 each, respectively in 1,000 piece quantities.

The LT3973HDD and LT3973HMSE are tested and guaranteed to operate from a -40 to 150°C operating junction temperature and are priced at $3.38 and $3.49 each, respectively in 1,000 piece quantities All versions are available from stock.      

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