Step-down converter with extremely low quiescent current targets always-on applications

July 19, 2012 // By Paul Buckley
Linear Technology Corporation has introduced the LT3975, a 42 V step-down switching regulator that can deliver 2.5 A of continuous output current and requires only 2.7 µA of quiescent current.

Similarly, the LT3976 can operate from a 40 V input, delivers up to 5 A of output current and requires 3.3 µA of quiescent current. Both devices offer a 4.2 V to a nominal 40 V input voltage range, making them ideal for automotive and industrial applications. Their internal high 75mOhm switches deliver efficiencies as high as 90%. The LT3975’s and LT3976’s Burst Mode operation offers ultralow quiescent current, a feature that is also well suited for automotive and industrial systems applications that demand always-on operation and optimum battery life.

The devices’ design maintains a minimum dropout voltage of 500 mV when the input voltage drops below the programmed output voltage, a functional necessity in applications subject to automotive cold-crank conditions. Switching frequency is user-programmable from 200 kHz to 2 MHz, and synchronizable from 250kHz to 2MHz, enabling the designer to optimize efficiency while avoiding critical noise-sensitive frequency bands. The combination of their 16-lead thermally enhanced MSOP package and high switching frequency keeps external inductors and capacitors small, providing a compact, thermally efficient footprint.

The LT3975 and LT3976 use a high efficiency 75 mOhm switch, with the boost diode, 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 15 mVPK-PK. Special design techniques and a new high voltage process deliver high efficiency over a wide input voltage range, and their current-mode topology enables fast transient response and excellent loop stability. Other features include a power good flag, soft-start capability and thermal protection.

Availability and Pricing

The LT3975EMSE and the LT3976EMSE are packaged in a thermally enhanced MSOP-16, priced starting at $3.10 and $3.75 each, respectively for 1,000-piece quantities. The LT3975IMSE and LT3976IMSE are tested and guaranteed to operate from a -40 to 125°C operating junction temperature and are priced at $3.41 and $4.13 each, respectively in 1,000-piece quantities. The LT3975HMSE and LT3976HMSE