Power Electronics

Synchronous PWM Controller

Linear Technology Corp.’s new LTC3723 push-pull synchronous PWM controller is specifically targeted toward compact and highly efficient isolated power supplies. The LTC3723 controller's basic features, its flexibility and support for secondary synchronous rectifiers (with adjustable timing) make it suitable for virtually all isolated, synchronous topologies. The LTC3723 is especially suited for converting high-voltage backplane (36-V to 72-V) rails to 12 V (distributed bus) and lower voltages at power levels between 100 W and 750 W. Single-ended synchronous topologies offer simple solutions to medium-power applications. The push-pull and half/full-bridge configurations offer smaller input filter and output inductors (operating at twice the frequency of single-ended converters), up to 40% greater transformer utilization and balanced semiconductor dissipation over the input line range. The LTC3723 includes many new features, which simplify and reduce component count in all the isolated topologies.

The IC integrates two robust 1.5-A sink, 1-A source primary MOSFET drivers as well as two synchronous secondary outputs. The addition of secondary synchronous MOSFETs results in operating efficiencies of 90% to 96% (a 5% improvement over conventional non-synchronous solutions). The LTC3723 is equipped with adjustable dead-time and synchronous timing, leading-edge blanking, accurate current sense, adjustable slope compensation, undervoltage lockout and low start-up current (for bootstrap start from high input voltages).

The LTC3723 is housed in a 16-lead SSOP package and can be used in applications such as industrial, automotive, avionics and telecom isolated power supplies. It also provides short-circuit and overtemperature protection. The IC is offered in two versions, current mode (LTC3723-1) and voltage mode (LTC3723-2). The LTC3723-1 features peak current mode control with programmable slope compensation and leading edge blanking. The LTC3723-2 employs voltage mode control with voltage feed-forward capability. Both devices feature extremely low start-up and operating currents of 145 µA and 3mA, respectively. The LTC3723-1 and LTC3723-2 are rated for operation from –40°C to 85°C.

For more information, visit www.linear.com.

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