About UsPower over Ethernet Device Controller Designed for Low-Voltage Auxiliary Power Sources
National Semiconductor has released the industry's first single-chip solution specifically designed for Power over Ethernet (PoE) devices
National Semiconductor (now part of Texas Instruments) has released a single-chip solution specifically designed for
Power over Ethernet (PoE) devices that operate from alternative power sources or the PoE-enabled network.
The LM5071 is a Powered Device (PD) interface and DC-DC converter IC that simplifies the design of a variety of
PoE applications that require an auxiliary power source such as an AC adapter.
Devices powered by a PoE network include IP phones, security cameras and wireless local area network (WLAN) nodes connected through Ethernet networking cables and ports. Operating these PoE devices from alternate power sources is often necessary to relieve the burden on the Power Sourcing Equipment (PSE) or to operate the device on a network that is not PoE-enabled. Current solutions limit the choice of auxiliary power sources, which can drive up overall system cost or complexity.
National’s LM5071 is the industry’s first single-chip, IEEE 802.3af-compliant PD interface port and pulse-width modulator (PWM) controller specifically designed to accept power from external AC adapters. The LM5071 integrates a PD front end that accepts power from the PSE or auxiliary power to a single chip with a DC-DC controller that steps down the input voltage to power various PD loads.
“Powering the device from an AC adapter can be tricky and requires forethought by the IC designer. The LM5071 solves the auxiliary power interface problem encountered by many PoE equipment designers with an elegant, integrated PD solution,” said Paul Greenland, director of strategic marketing for National Semiconductor's Power Management group. “This new addition to National's PoE power product family accepts a wide range of AC adapter voltages, giving equipment designers the flexibility to optimize total system cost. The LM5071 builds on the success and learnings of its predecessor, the LM5070, to provide an auxiliary-powered PD solution that is superior to any on the market today.”
Key Technical Specifications
The LM5071 is fabricated with National's ABCD150-XV1 high-voltage analog bipolar/CMOS/DMOS technology and
offers advantages such as an integrated, high-frequency, current-mode DC-DC controller,
user-programmable under-voltage threshold and hysteresis, and a highly accurate fault current control loop.
It features a maximum input voltage of 80V, user-programmable oscillator frequency up to 1 MHz and over-temperature protection,
plus a voltage reference and high-performance error amplifier for non-isolated applications.
Features of the LM5071 include:
- Auxiliary power interface: Accepts a wide range of auxiliary power source voltages (12V to 48V) and activates the DC-DC converter to efficiently supply the various loads of the PD
- UVLO threshold and hysteresis: Designers can program the under-voltage lockout (UVLO) trip-point and hysteresis completely independently
- Controls isolated or non-isolated DC-DC converters: Integrates the precision voltage reference and error amplifier for DC-DC feedback in non-isolated converters, including the simple Buck topology.
- Signature resistor disconnect: The 25 kilohm signature resistor is disconnected after PD detection to reduce power loss.
- Programmable oscillator frequency: The oscillator for the switching regulator controller is fully programmable, allowing the user to optimize regulator performance.
- 50 percent or 80 percent maximum duty cycle: Available with either 50 percent or 80 percent maximum PWM duty cycle to support a variety of DC-DC converter topologies and permit operation over an extended input voltage range.
The Texas Instruments website address is www.ti.com
[Reprinted with kind permission from National Semiconductor]