Controller eliminates external surge protection devices
A high voltage, non-isolated, synchronous step-down switching regulator controller, the LTC7801, is available from Analog Devices, in compact 24-lead packages that drives an all N-channel metal oxide semiconductor field effect transistor (MOSFET) power stage.
The LTC7801’s 4.0 to 140V (150V 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 LTC7801 continues to operate at up to 100 per cent duty cycle during input voltage dips down to 4.0V, 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 per cent. The device draws only 40-microA in sleep mode with the output voltage in regulation, making it suitable for always-on systems. An internal charge pump allows for 100 per cent duty cycle and operation in dropout. This is a useful feature when powered from a battery during discharge, points out Analog Devices. The LTC7801’s powerful one-Ohm N-channel MOSFET gate drivers can be adjusted from 5.0 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 LTC7801 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 LTC7801 to be powered from the output of the switching regulator or other available source, reducing power dissipation and improving efficiency.
The LTC7801 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 sensing 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 an integrated bootstrap diode, a power-good output signal, adjustable input over-voltage lockout and soft-start.
The LTC7801 is available in 4.0 x 5.0mm QFN-24 and TSSOP-24 thermally enhanced packages. Two operating junction temperature grades are available, extended and industrial versions from -40 to +125 degree C and a high temp automotive version from -40 to +150°C.