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150V Synchronous Step-Down DC/DC Controller Eliminates External Surge Protection Devices

Analog Devices » LTC7801

Analog Devices, Inc., which recently acquired Linear Technology Corporation, announces the LTC7801, a high voltage nonisolated synchronous step-down switching regulator controller in compact 24-lead packages that drives an all N-channel MOSFET power stage. Its 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 LTC7801 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 datacom applications.

Analog Devices - LTC7801

The 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%. The device draws only 40 μA in sleep mode with the output voltage in regulation, ideal for always-on systems. An internal charge pump allows for 100% duty cycle and operation in dropout, a useful feature when powered from a battery during discharge. The LTC7801’s powerful 1 Ω 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 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 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 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 80 ns 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 overvoltage lockout and soft-start.

Efficiency and Power Loss vs Load Current
Efficiency and Power Loss vs Load Current.

The LTC7801 is available in 4 mm × 5 mm QFN-24 and TSSOP-24 thermally enhanced packages. Two operating junction temperature grades are available: extended and industrial versions from –40 to 125 °C and a high temp automotive version from –40°C to 150 °C. The 1,000-piece price starts at $4.20 each.

Summary of Features: LTC7801

  • Wide Input Voltage Range: 4 V to 140 V (150 V Abs Max)
  • Wide Output Voltage Range: 0.8 V to 60 V
  • Output Current up to 20 A
  • Synchronous Rectification for Up to 96% Efficiency
  • Low 40 μA Quiescent Current
  • 100% Duty Cycle Capability
  • Adjustable 5 V-10 V Gate Drive Voltage for Logic-Level or Standard Threshold MOSFETs
  • DCR or RSENSE Current Sense
  • Low 80 ns Minimum On-Time for High Step-Down Ratios
  • Selectable Continuous, Pulse-Skipping or Low Ripple Burst Mode® Operation at Light Loads
  • Selectable Fixed Operating Frequency from 50 kHz to 900 kHz
  • PLL Synchronizable Operating Frequency from 75 kHz to 850 kHz
  • Current Mode Control for Fast Transient Response & Easy Loop Compensation
  • Power Good Output Signal
  • Adjustable Input Overvoltage Lockout

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