Industrial & Medical Technology

Step-Down DC/DC Controller Eliminates External Surge Protection Devices

27 May 2016

The LTC3895 from Linear Technology Corporation is a high-voltage, non-isolated synchronous step-down switching regulator controller that drives an all N-channel MOSFET power stage. The controller’s 4 V to 140 V (150 V 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 4 V, making it well suited for transportation, industrial control, robotic and data-communication applications.

LTC3895 synchronous step-down switching regulator controller. Source: Linear Technology LTC3895 synchronous step-down switching regulator controller. Source: Linear Technology

The controller’s output voltage can be set from 0.8 V to 60 V at output currents up to 20 A with efficiencies as high as 96%. This part draws only 40µA in sleep mode with the output voltage in regulation, ideal 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 5 V to 10 V 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 that 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 850kHz. The user can select from forced continuous operation, pulse-skipping or low-ripple Burst Mode® operation during light loads. Its current- mode architecture provides easy 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. A low 80ns minimum on-time allows for high step-down ratios at high switching frequency. Current foldback limits MOSFET heat dissipation during overload conditions.

Additional features include a fixed 5 V or 3.3 V output option, integrated bootstrap diode, a power-good output signal, adjustable input overvoltage lockout and soft-start.

The LTC3895 is available in a TSSOP-38 thermally enhanced package with several pins removed for high voltage spacing. Two operating junction temperature grades are available with extended and industrial versions from -40° C to 125° C, and a high-temperature automotive version from -40° C to 150° C. The 1,000-piece price starts at $4.70 each. 

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