UCC28501 Datasheet | Texas Instruments

FEATURES D bines PFC and Downstream Converter Controls D Controls Boost Preregulator to Near-Unity Power Factor D Accurate Power Limiting D Improved Feedforward Line Regulation D Peak Current-Mode Control in Second Stage D Programmable Oscillator D Leading-Edge/Trailing-Edge Modulation for Reduced Output Ripple D Low Start-up Supply Current D Synchronized Second Stage Start-Up, with Programmable Soft-start D Programmable Second Stage Shutdown DESCRIPTION The UCC2850x family provides all of the control functions necessary for an active power-factorcorrected preregulator and a second-stage dc-to- dc converter. The controller achieves near-unity power factor by shaping the ac input line current waveform to correspond to the ac input-line voltage using average current-mode control. The dc-to-dc converter uses peak current-mode control to perform the step-down power conversion. The PFC stage is leading-edge modulated while the second stage is trailing-edge synchronized to allow for minimum overlap between the boost and PWM switches. This reduces ripple current in the bulk-output capacitor.In order to operate with over three-to-one range of input-line voltages, a line feedforward (VFF) is used to keep input power constant with varying input voltage. Generation of VFF is acplished using IAC in conjunction with an external single-pole filter. This not only reduces external parts count, but also avoids the use of high-voltage ponents, offering a lower-cost solution. The multiplier then divides the line current by the square of VFF. The UCC2850x PFC section incorporates a low offset-voltage amplifier with 7.5-V reference, a highly-linear multiplier capable of a wide current range, a high-bandwidth, low offset-current amplifier, with a novel noise-attenuation configuration, PWM parator and latch, and a high-current output driver. Additional PFC features include over-voltage protection, zero-power detection to turn off the output when VAOUT is below 0.33 V and peak current...