Analog Devices LT4275 | Demoboard DC1788A

Description

Demonstration circuit 1788A features the LT®4275, a fourth generation powered device (PD) controller for Power over Ethernet (PoE) applications.

The DC1788A is available in DC1788A-A, DC1788A-B, and DC1788A-C versions to meet the power level required by the PD application. The DC1788A-A features the LT4275A PD controller. This controller supports the IEEE 802.3at(Type 2, PoE+), IEEE 802.3af (Type 1, PoE) and LTPoE++™ specification.LTPoE++ adds four power levels to the existing IEEE standard with 38.7W, 52.7W, 70W, and 90W of delivered PD power at the RJ45 jack. The DC1788A-B features the LT4275B PD controller and is compliant withthe IEEE 802.3at and IEEE 802.3af specifications.The DC1788A-C features the LT4275C PD controller and is compliant with the IEEE 802.3af specification.

The DC1788A includes an RJ45 Ethernet port, a high power Ethernet magnetic, a discrete active bridge rectifier,a surge protector, an external N-channel FET, and the LT4275. The discrete active bridge rectifier is used toachieve higher efficiency than a conventional diode bridge rectifier. Many of the main features from the previous generation PD controller are included in this generation PDcontroller. These include a power good indicator, a power sourcing equipment (PSE) type indicator, and support for an auxiliary power input. The major difference from the previous generation PD controller is that the LT4275 drives an external N-channel Hot Swap™ FET at the PoE high side voltage rail. This allows the user to choose a lowRDS(ON) N-channel MOSFET to maximize power efficiency,reduce heat dissipation, and ease thermal design. An LED status indicator is included to indicate the Hot Swap FET is fully turned on and the PSE is powering the PD. A sufficient load to sink more than 10mA is also included to assure the PSE maintains power to the PD and to meet the DC maintain power signature current required by the IEEE 802.3at/IEEE 802.3af specification.

Simply connect the output of the DC1788A to the DC/DC converter that is right for the application. Linear Technology offers a variety of DC/DC converter solutions that can be used with the DC1788A (eg DC894, DC1317, etc).

More information

• Datasheet
• IC product information