Kinetic Technology KTA1137A

Description

Most PoE PD applications use an isolated converter topology, and the available controllers are designed for this configuration. However, they may also be used for non-isolated topologies. The 802.3af/at/bt PoE standards specify input to output isolation, but many low-cost applications comply using other techniques. If the PD system ground is constrained to a single point (the source Ethernet cable), and there are no other connectors and no access to non-isolated conductors, a non-isolated power supply complies with the standard.There are two configurations possible for the non-isolated Buck. The Buck topology may be configured with Vin(-) as the common input to output connection, or it may be configured with Vin(+) as the common input to output connection. The former is referred to as a low-side Buck, and the latter a high-side Buck; in reference to the location of the common rail. Each has its advantages and disadvantages. Both have the PD/DC-DC controller IC referenced to Vin(-), so either the FET driver output and current sense signal must be level shifted to or from the floating gate-source, or the feedback signal must be level-shifted to IC ground reference Vin(-). For simplification and clarity, VIN is defined as Vin(+) – Vin(-) and VOUT is defined as Vout(+) – Vout(-).A non-isolated topology reduces the cost and complexity of the power conversion function in a PD, so its appeal is obvious. However, there are some disadvantages to the Buck topology regardless of configuration which will be discussed later in this application note.

Features

• Full support of both IEEE® Std. 802.3af-2005 and IEEE® Std. 802.3at-2009 power requirements
• “2-Event” classification for 802.3at higher power PDs
• Robust Type 2 PSE detector with proprietary digital filtering for line noise to eliminate false positives
• IEC 61000-4-2/3/4/5/6 requirements for EMC Compliance
• Integrated Surge Protection for 15kV/8kV System level ESD Compliance
• Exceptional EMI performance
• Programmable DC current limit up to 730mA for 30W applications
• Seamless support for local power, down to 9.5V
• Low Rds-on Hot-Swap FET (typical 0.6Ω)
• Integrated Short-Circuit Protection
• Over temperature protection
• 5×5 mm, 20 lead QFN Package
• Industrial temperature range (-40°C to +85°C)

Typical applications

• Fiber-to-the-home (FTTH) terminals, Wireless LAN access points, WiMAX terminals, an, tilt and zoom (PTZ), security and web cameras, Voice over IP (VoIP) phones
• Thin clients and notebook computers

More information

• Datasheet
• IC product information