150V DC/DC inverting controller: single inductor, ground-referenced control

May 26, 2016 // By Graham Prophet
LTC3896 is a high voltage inverting switching regulator controller that drives an all N-channel synchronous power MOSFET stage. Most low to medium power inverting DC/DC converters use a coupled inductor or transformer: this device uses only a single inductor.

The chip converts a 4V to (150V - |VOUT‾|) positive input voltage to a regulated negative output voltage from -60V to -0.8V at output currents up to 15A. Efficiencies are as high as 96%, for transportation, industrial, telecom 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 40 µA in sleep mode with the output voltage in regulation, for always-on systems. The LTC3896’s 1Ω N-channel MOSFET gate drivers can be adjusted from 5V to 10V 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 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 it 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 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 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.

 

In a TSSOP-38 thermally enhanced package with several pins removed for high voltage spacing, there are two operating junction temperature grades with extended and industrial versions from -40°C to 125°C and a high temp automotive version from -40°C to 150°C.