Switching regulator integrates LDOs for accurate tracking

Posted By : Siobhan O'Gorman
Switching regulator integrates LDOs for accurate tracking

A 400mA, 40V step-down switching regulator with dual tracking LDO outputs has been released by Linear Technology. Operating from a VIN range of 4.3-40V with transient protection to 60V, the LT3668 is particularly suitable for automotive and industrial applications. Up to 400mA can be delivered by the internal 600mA switch and 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, while each LDO can deliver outputs as low as 1.1V. When all three channels are in regulation, the regulator requires only 50µA of quiescent current, making it suitable for always-on automotive applications.

Allowing the designer to optimise efficiency while avoiding critical noise-sensitive frequency bands, the device’s switching frequency is user programmable from 250kHz to 2.2MHz. Ensuring reliability, each integrated tracking LDO has an accurate programmable current limit up to 200mA. The high accuracy which the LDOs provide make them suitable for powering ADCs and sensors. Powering the LDOs from the primary switching output rather than the independent inputs provides both high efficiency and low noise.

The necessary oscillator, control, and logic circuitry are integrated into the main switcher’s 600mA switch. While the regulator’s current mode topology enables fast transient response and loop stability, it’s design enables high efficiency over a wide input voltage range. A power indicator, synchronisation capability, reverse-battery protection, current and thermal limiting and programmable undervoltage lockout are also featured.

The LT3668 is suitable for applications that require the power supply of a sensor to track the power supply of a measurement ASIC. A compact, thermally efficient footprint is provided by the combination of the device's thermally enhanced MSOP-16E and high switching frequency, which allow external capacitors and inductors to be small in size.

Offered in a 16-lead MSOP package, the LT3668EMSE is sold in 1,000-piece quantities and priced at $2.55 each. The LT3668IMSE, which is tested and guaranteed to operate from a -40 to 125°C operating junction temperature, is sold in the same quantities and priced at $2.81 each.


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