Inverting DC/DC controller offers efficiencies up to 96%

26th May 2016
Nat Bowers

Driving an all N-channel synchronous power MOSFET stage, the LTC3896 high voltage inverting switching regulator controller has been unveiled by Linear Technology. Most low to medium power inverting DC/DC converters utilise a coupled inductor or transformer. However, the LTC3896 uses only a single inductor and converts a 4V to 150V positive input voltage to a regulated negative output voltage from -60 to -0.8V at output currents up to 15A.

Efficiencies as high as 96% make the LTC3896 suitable for transportation, industrial, telecomms and power distribution applications.

The LTC3896 contains true ground-referenced control pins, eliminating the need for discrete level-shifting components for its interface. This part draws only 40µA in sleep mode with the output voltage in regulation, ideal for always-on systems. The LTC3896’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 LTC3896 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 LTC3896 to be powered from its output voltage or other bias supply, which reduces power dissipation and improves efficiency.

The LTC3896 operates with an adjustable 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. Current foldback limits MOSFET heat dissipation during overload conditions. Additional features include adjustable burst clamp and current limit, a power good output signal, an integrated bootstrap diode and adjustable soft-start.

The LTC3896 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. 1,000 unit pricing starts at $4.70 each.

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