140V, 400 mA step-down converter uses 12 µA quiescent

February 06, 2015 // By Graham Prophet
LTC7138 is a 140V input-capable high efficiency buck converter that delivers up to 400 mA of continuous output current. It operates from an input voltage range of 4V to 140V, suiting it for a wide range of telecom, industrial, avionic and automotive applications.

LTC7138 uses a programmable hysteretic mode design to optimise efficiency over a broad range of output currents. It has an internal 1.8 Ohm power MOSFET for robust, high efficiency operation. A user-programmable output current limit can set output current from 100 mA to 400 mA as required by the particular application. The device can be programmed with fixed output voltages of 1.8V, 3.3V or 5V, or a resistor divider can be used to program outputs from 0.8V to VIN. Its thermally enhanced MSOP offers additional pin spacing required for high voltage inputs. The combination of its MSOP and only four tiny externals provides a highly compact solution footprint for a wide array of applications.

The LTC7138 draws 12 µA at no load while maintaining output voltage regulation, making it suitable for always-on battery-powered applications. Due to the inherent stability of the converter, no external compensation is required thereby simplifying design and minimising the solution footprint. Features include a precise 0.8V ±1% feedback voltage reference, 100% duty cycle dropout operation and internal or external soft-start, plus a feedback comparator output which enables multiple LTC7138s to be connected in parallel for higher current applications.

Pricing for the LTC7138EMSE, starts at $3.80 (1000). An industrial temperature version, LTC7138IMSE, is guaranteed to operate from a -40°C to 125°C operating junction temperature and is priced at $4.18. An automotive temperature version, LTC7138HMSE, is specified to operate from a -40°C to 150°C operating junction temperature and is priced at $4.43. Finally, a high reliability version, LTC7138MPMSE, is tested and guaranteed to operate from a -55°C to 150°C operating junction temperature and is $11.29.

Linear Technology; www.linear.com/product/LTC7138