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 two upper drivers are driven
at a fixed 50% duty cycle.
This IC integrates many features in 28 Ld SOIC package 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 triggering 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 features include adjustable cycle-by-cycle peak
current limiting 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 to
accept an enable command when monitoring the input voltage
and thermal condition of a converter and VDD undervoltage
lockout with hysteresis. Additionally, the ISL6551 includes
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 feedback loop
compensation, a precision bandgap reference with ±1.5%
(ISL6551AB) or ±1% (ISL6551IB) tolerance across
recommended operating conditions and a ±5% “in regulation”
monitor.

Features
• High speed PWM (up to 1MHz) for ZVS full bridge control
• Current mode control compatible
• High current high-side and low-side totem-pole drivers
• Adjustable resonant delay for ZVS
• 10MHz error amplifier bandwidth
• Programmable soft-start
• Precision bandgap reference
• Latching shutdown input
• Non-latching enable input
• Adjustable leading edge blanking
• Adjustable dead time control
• Adjustable ramp for slope compensation
• Fast short-circuit protection (hiccup mode)
• Adjustable cycle-by-cycle peak current limiting
• Drive signals to implement synchronous rectification
• VDD undervoltage lockout
• Current share support
• ±5% “in regulation” indication
• Pb-free (RoHS compliant)

Applications
• Full-bridge and push-pull converters
• Power supplies for off-line and Telecom/Datacom
• Power supplies for high end microprocessors and servers