The TPS23754 and TPS23756 devices have a combined power-over-ethernet
(PoE), powered-device (PD) interface, and current-mode DC-DC controller optimized specifically for
isolated converters. The PoE interface supports the IEEE 802.3at standard.
The TPS23754 and TPS23756 support 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 new extended hardware 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-DC controller features two complementary gate drivers with programmable dead time.
This simplifies the design of active-clamp forward converters or optimized gate drive for
highly-efficient flyback topologies. The second gate driver may be disabled if desired for single
MOSFET topologies. The controller also features internal soft start, bootstrap start-up 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.
The TPS23754 device has a 15-V converter start-up while the TPS23756 device has a 9-V
converter start-up. The TPS23754-1 replaces the PPD pin with a no-connect for increased pin