Controller eliminates the need for external surge protection

Posted By : Nat Bowers
Controller eliminates the need for external surge protection

Driving an all N-channel MOSFET power stage, the LTC3895 high voltage non-isolated synchronous step-down switching regulator controller has been unveiled by Linear Technology. Its 4 to 140V (150V absolute maximum) 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, making it well suited for transportation, industrial control, robotic and datacomms applications.

The output voltage can be set from 0.8 to 60V at output currents up to 20A with efficiencies as high as 96%. This part draws only 40µA in sleep mode with the output voltage in regulation, suited 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 powerful 1Ω N-channel MOSFET gate drivers can be adjusted from 5 to 10V to enable the use of logic- or standard-level MOSFETs to maximise 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 and 900kHz and is synchronisable to an external clock from 75 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 or 3.3V 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 to +125°C and a high temp automotive version from -40 to +150°C. Prices start at $4.70 each in 1,000 unit quantities.

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