40V, 400mA (IOUT), 2.2MHz Step-Down Regulator with Dual Tracking LDO

Crystal oscillator

Photocoupler

Linear Technology Corporation (Linear Technology Corporation) Release 400mA, 40V step-down switching regulator LT3668, the device comprising dual track LDO output, using the MSOP-16E. The LT3668 provides a complete and rugged power solution for applications that require sensor power to closely track the power of the measurement ASIC. Operating over a VIN range of 4.3V to 40V, the LT3668 features 60V transient protection, making it ideal for automotive and industrial applications. Its internal 600mA switch can deliver up to 400mA, which is distributed to the combined output of the main output and two tracking LDOs . The main switch channel can provide outputs as low as 1.2V, and each LDO can provide outputs as low as 1.1V. When all three channels are in a stable state, the LT3668 requires only 50μA of quiescent current, making the device ideal for automotive applications that are always on.

The LT3668's switching frequency is user-programmable from 250kHz to 2.2MHz, allowing designers to optimize efficiency while avoiding critical noise-sensitive frequency bands. Each integrated tracking LDO has an accurate and programmable current limit of up to 200mA to ensure a higher level of reliability. The high accuracy of the tracking LDOs makes these LDOs ideal for powering ADCs and sensors. Although these LDOs can be powered by independent inputs, powering them with the main switch output can achieve both high efficiency and low noise. The LT3668's thermally enhanced MSOP-16E package combines with a high switching frequency (allowing the use of small external capacitors and inductors) to form a compact thermal efficiency solution.

The LT3668's main switch features a high efficiency 600mA switch with the necessary oscillator, control and logic circuitry integrated into a single chip. A special design approach enables high efficiency over a wide input voltage range, while the LT3668's current mode topology enables fast transient response and excellent loop stability. Other features include power indicator, synchronization, battery reverse protection, current limit and overtemperature limits, and programmable undervoltage lockout.

The LT3668EMSE is available in a thermally enhanced 16-lead MSOP package for $2.55 each. The LT3668IMSE has been tested and is guaranteed to operate over the –40°C to 125°C operating junction temperature range at $2.81 each. All prices are in a single piece price in 1,000-piece quantities and all versions are available from stock. For more information, please visit

Photo Caption: 40V, 400mA (IOUT), Triple Output DC/DC Converter

Performance Summary: LT3668

Single-input, three-output power supply requires only one inductor

·Double low dropout linear tracking regulator

200mA output with programmable current limit

1.6V to 45V input range

Fault protection to ±45V

·Buck regulator

Low Ripple (<15mVP-P) Burst Mode?

400mA output with internal power switch

4.3V to 40V input working range (maximum 60V)

• IQ = 50μA at 12VIN to 6V, 5V and 5V output without load

·250kHz to 2.2MHz adjustable switching frequency

· Syncable from 300kHz to 2.2MHz

·Programmable undervoltage lockout

·Power good indicator

· Thermally enhanced 16-lead MSOP package