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