150V synchronous step-down DC/DC includes surge protection

May 23, 2016 // By Graham Prophet
Linear Technology designed the LTC3895 to be a non-isolated DC/DC controller with a high input voltage capability that can eliminate the need for surge suppression and operate continuously with a high input voltage.

The synchronous step-down switching regulator controller drives an all N-channel MOSFET power stage. Its 4V to 140V (150V abs. Max.) input voltage range is designed to operate from a high input voltage source or from an input that has high voltage surges, eliminating the need for external surge suppression devices. The LTC3895 continues to operate at up to 100% duty cycle during input voltage dips down to 4V, for transportation, industrial control, robotic and datacom applications.


The output voltage can be set from 0.8V to 60V at output currents up to 20A with efficiencies as high as 96%. This part draws only 40 µA in sleep mode with the output voltage in regulation, for always-on systems. An internal charge pump allows for 100% duty cycle operation in dropout, a useful feature when powered from a battery during discharge. The LTC3895’s 1Ω N-channel MOSFET gate drivers can be adjusted from 5V to 10V to enable the use of logic- or standard-level MOSFETs to maximize efficiency. To prevent high on-chip power dissipation in high input voltage applications, the LTC3895 includes an NDRV pin which drives the gate of an optional external N-channel MOSFET acting as a low dropout linear regulator to supply IC power. The EXTVCC pin permits the LTC3895 to be powered from the output of the switching regulator or other available source, reducing power dissipation and improving efficiency.


The LTC3895 operates with a selectable fixed frequency between 50 kHz and 900 kHz and is synchronizable to an external clock from 75 kHz to 850 kHz. The user can select from forced continuous operation, pulse-skipping or low ripple Burst Mode operation during light loads. Its current mode architecture provides simple loop compensation, fast transient response and excellent line regulation. Current sensing is accomplished by measuring the voltage drop across the output inductor (DCR) for highest efficiency or by using an optional sense resistor. An 80 nsec minimum on-time allows