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2.25MHz for 60V step-down controller boosts power density

2.25MHz for 60V step-down controller boosts power density

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By Nick Flaherty



The low 45ns minimum on-time of the LTC7800 enables 24 VIN to 3.3 VOUT conversions while switching at a fixed 2MHz, avoiding critical noise-sensitive frequency bands including AM radio. Synchronous rectification delivers up to 95% efficiency while Burst Mode operation keeps quiescent current under 50μA in no-load standby conditions for always-on systems.

The LTC7800 operates over a 4V to 60V input supply range designed to protect against high voltage transients, continuous operation during automotive cold crank and to cover a broad range of input sources and battery chemistries. The output voltage can be set from 0.8V to 24V at output currents up to 20A, well suited for 12V or 24V automotive, heavy equipment, industrial control, robotics and telecom applications.

The LTC7800 has 1.1Ω on-chip MOSFET gate drivers and a selectable fixed frequency between 320kHz and 2.25MHz that is synchronised to an external clock over the same range. The user can select from continuous operation, pulse-skipping and low ripple Burst Mode operation during light loads. The current mode architecture provides easy loop compensation, fast transient response and excellent line regulation.

Output current sensing is accomplished by measuring the voltage drop across the output inductor (DCR) for the highest efficiency or by using an optional sense resistor. Current foldback limits MOSFET heat dissipation during overload conditions. Additional features include up to 98% duty cycle (useful when powered from a battery during discharge), an internal LDO that powers the gate drive from the input voltage or external VCC and a power good output signal.

The LTC7800 is available in a 20-lead 3mm x 4mm QFN thermally enhanced package which is pin compatible to the LTC3891. Two operating junction temperature grades are available with extended and industrial versions from –40 to 125°C and a high temp automotive grade version from –40°C to 150°C. The 1,000-piece price starts at $3.47.

For more information, visit www.linear.com/product/ltc7800.

 

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