The TPS23785B is a combined Power over Ethernet (PoE) powered device
(PD) interface and current-mode DC-to-DC controller optimized specifically for non-isolated
converters. The PoE interface supports the IEEE 802.3at standard.
The TPS23785B supports a number of input voltage ORing options including
highest voltage, external adapter preference, and PoE preference. These features allow the designer
to determine which power source will carry the load under all conditions.
The PoE interface features the two-event, physical-layer classification necessary for
compatibility with high-power midspan power sourcing equipment (PSE) per IEEE 802.3at. The
detection signature pin can also be used to force power from the PoE source off. Classification can
be programmed to any of the defined types with a single resistor.
The DC-to-DC controller features two complementary gate drivers with programmable dead
time. This simplifies design for highly-efficient flyback topologies utilizing secondary
synchronous rectification. The second gate driver may be disabled if desired for single MOSFET
topologies. The controller also features internal softstart, bootstrap startup source, current-mode
compensation, and a 78% maximum duty cycle. A programmable and synchronizable oscillator allows
design optimization for efficiency and eases use of the controller to upgrade existing power supply
designs. Accurate programmable blanking, with a default period, simplifies the usual current-sense
filter design trade-offs.
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