Texas Instruments' TPS23758 device combines a PoE PD interface, a 150 V switching power FET, and a current-mode DC/DC controller optimized for flyback topology. The high integration, primary-side regulation (PSR), spread spectrum frequency dithering (SSFD), and the advanced startup makes the TPS23758 an ideal solution for size-constrained applications. The PoE implementation supports the IEEE 802.3at standard as a 13 W, Type 1 PD.
The PSR feature of the DC/DC controller uses feedback from an auxiliary winding for control of the output voltage, eliminating the need for an external shunt regulator and an optocoupler. It is optimized for operation in continuous conduction mode (CCM) with secondary-side synchronous rectification, resulting in optimum overall efficiency, regulation accuracy, and step-load response over multiple outputs (i.e. 5 V and 3.3 V outputs). The converter can operate at a switching frequency of 250 kHz.
The SFFD and slew rate control help to minimize the size and cost of the EMI filter. The advanced startup allows the use of a minimal bias capacitor while simplifying converter startup and hiccup design. The primary auxiliary power-detect (APD) pin can be used to provide priority for a primary-side power adapter. The DC/DC controller features adjustable soft-start, slope compensation, and blanking. The TPS23758 supports buck topology for non-isolated applications.