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Full-bridge controller boasts adaptive ZVS

05 Apr 2013

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Linear Technology has recently announced the H-grade version of the LTC3722-1. The company's latest offering is a phase-modulated full bridge DC/DC controller with adaptive or manual zero voltage switching (ZVS).

The device's ZVS delay control and adjustable synchronous rectification timing optimise efficiency while reducing transformer size and electromagnetic interference, making it well suited for isolated high power applications of up to several kilowatts.

The LTC3722-1's adaptive zero voltage technology is accomplished by sensing the bridge MOSFETs and input voltage, allowing the converter to adapt to any change in load current, temperature, component tolerances, driver circuitry delay or input voltage variations. Additional features include fixed frequency current mode control, adjustable current limit, leading edge blanking, soft start, short-circuit protection and programmable slope compensation. An accurate 5V low dropout regulator provides up to 15mA to power auxiliary circuits.

The phase-shifted full bridge can be described by four primary operating states. The key to understanding how ZVS occurs is revealed by examining the states in detail. Each full cycle of the transformer has two distinct periods in which power is delivered to the output, and two "freewheeling" periods. The two sides of the external bridge have fundamentally different operating characteristics that become important when designing for ZVS over a wide load current range. The left bridge leg is referred to as the passive leg, while the right leg is referred to as the active leg. The following descriptions along with detailed descriptions in the data sheet provide insight as to why these differences exist.

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State 1 (Power Pulse 1).

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State 2 (Active Transition and Freewheel Interval)

fig3

State 3 (Passive Transition)

fig4

State 4 (Power Pulse 2)

The H-grade version operates up to a junction temperature of 150°C, compared to the E- and I-grade versions' 85°C maximum junction temperature. The H-grade product is tested and guaranteed to the maximum junction temperature of 150°C, making it ideal for automotive and industrial applications which are subjected to high ambient temperatures.

The IC is available in an SSOP-24 package. The 1000-piece price starts at $6.24 each for the H-grade device.

Datasheet for the H-grade version of the LTC3722-1 can be found here.




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