Combining the capabilities of two separate converters (buck and boost) has the advantage of reduced solution size and cost. Four-switch converters should be able to operate with just two switches for highest efficiency when only step-up or step-down conversion is needed. However, they must also be able to utilize four-switch operation as VIN and VOUT approach each other, and to transition gracefully between these regions of operation. Combining control loops for two-switch boost, two-switch buck, and four-switch operation, and designing nearly flawlessly transitions between these regions of operation has its challenges. However, the next generation of buck-boost converters masters these challenges and more.
The LT8391 60V four-switch buck-boost LED driver is designed to drive high power LEDs up to 250W and to flawlessly transition between two-switch boost, four-switch buck-boost, and two-switch buck regions of operation. A patent pending four-switch buck-boost current-sense resistor control scheme provides a simple, yet masterful method for the IC to run in peak current mode control in all regions of operation with a single sense resistor. This new generation buck-boost LED driver features spread spectrum frequency modulation and internally generated PWM dimming, which work together. The LT8391 has flicker-free PWM dimming with both internal and external PWM dimming, even when spread spectrum is turned on (another patent pending technique).