ISL6551

The ISL6551 is a zero voltage switching (ZVS) full-bridge PWM controller designed for isolated power systems. This part implements a unique control algorithm for fixed-frequency ZVS current mode control, yielding high efficiency with low EMI. The two lower drivers are PWM-controlled on the trailing edge and employ resonant delay while the twoupper drivers are driven at a fixed 50% duty cycle.

This IC integrates many features in both 6x6 mm QFN and 28-lead SOIC packages to yield a complete and sophisticated power supply solution. Control features include programmable soft-start for controlled start-up,programmable resonant delay for zero voltage switching, programmable leading edge blanking to prevent false riggering of the PWM comparator due to the leading edge spike of the current ramp, adjustable ramp for slope compensation, drive signals for implementing synchronous rectification in high output current, ultra high efficiency applications, and current share support for paralleling up to 10 units, which helps achieve higher reliability and availability as well as better thermal management. Protective eatures include adjustable cycle-by-cycle peak current imiting for overcurrent protection, fast short-circuit protection (in hiccup mode), a latching shutdown input to turn off the IC completely on output overvoltage conditions or other extreme and undesirable faults, a non-latching enable input o accept an enable command when monitoring the input voltage and thermal condition of a converter, and VDD under voltage lockout with hysteresis. Additionally, the ISL6551 ncludes high current high-side and low-side totem-pole drivers to avoid additional external drivers for moderate gate capacitance (up to 1.6nF at 1MHz) applications, an uncommitted high bandwidth (10MHz) error amplifier for eedback loop compensation, a precision bandgap reference with ±1.5% (ISL6551AB) or ±1% (ISL6551IB) tolerance over recommended operating conditions, and a ±5% "in regulation" monitor.