40V, 400mA output, step-down regulator has dual tracking LDOs

October 21, 2014 // By Graham Prophet
LT3668 is a 400mA, 40V step-down switching regulator with dual tracking LDO outputs packaged in an MSOP-16E. The LT3668 offers a complete, robust power solution for applications that require the power supply of a sensor to tightly track the power supply of a measurement ASIC.

The LT3668 operates from a VIN range of 4.3V to 40V with transient protection to 60V, making it suitable for automotive and industrial applications. Its internal 600 mA switch can deliver up to 400 mA, which is distributed to the combined loads of the primary output and both of the tracking LDOs. The primary switching channel can deliver outputs as low as 1.2V, and each LDO can deliver outputs as low as 1.1V. The LT3668 requires only 50 µA of quiescent current when all three channels are in regulation, making it appropriate for always-on automotive applications.

The LT3668's switching frequency is user programmable from 250 kHz to 2.2 MHz, enabling the designer to optimise efficiency while avoiding critical noise-sensitive frequency bands. Each integrated tracking LDO has an accurate programmable current limit up to 200 mA to ensure an additional level of reliability. The high accuracy of the tracking LDOs suits them for powering ADCs and sensors. Although the LDOs can be powered by independent inputs, powering them from the primary switching output offers both high efficiency and low noise. The combination of its thermally enhanced MSOP-16E and high switching frequency, which keeps external capacitors and inductor small, provides a compact, thermally efficient footprint.

The LT3668’s main switcher uses a high efficiency 600 mA switch, with the necessary oscillator, control, and logic circuitry integrated into a single die. Special design techniques enable high efficiency over a wide input voltage range, and its current mode topology enables fast transient response and excellent loop stability. Other features include a power indicator, synchronisation capability, reverse-battery protection, current and thermal limiting and programmable undervoltage lockout.

The LT3668EMSE comes in a thermally enhanced 16-lead MSOP package for $2.55 each. The LT3668IMSE version operates from -40°C to 125°C operating junction temperature and is priced at $2.81.

Linear Technology: www.linear.com/product/LT3668