NATIONAL Semiconductor, represented in Australia by Arrow Electronics , has released the LM5070 single-chip power device (PD) which simplifies the design of systems that use Power over Ethernet (PoE).
The LM5070 is a single-chip PD interface port and pulse-width modulator (PWM) controller that meets the IEEE 802.3af standard. It integrates an 80V, 400mA line connection switch and associated PoE interface circuits with a dc-dc controller that steps down the 48V input to power various loads.
It features a maximum operating voltage of 75V, user-programmable oscillator frequency up to 1MHz and over-temperature protection, plus a voltage reference and high-performance error amplifier for non-isolated applications.
The designer can program the under-voltage lockout (UVLO) trip-point and hysteresis independently. This allows him or her to control start-up line currents and program the start and stop voltage points as desired for a variety of system applications.
Designers also have full control over the inrush transient, which is programmed to the current desired via an external resistor on the RCLP pin. If the default inrush limit (375mA) is desired, no external components are required.
The designer does not have to control the dc-dc converter system with power good signals or any other external communications interface. Communication between the POE PD interface section and the dc-dc converter is completely integrated within the LM5070.
The 25kΩ signature resistor is disconnected after PD detection to avoid power and efficiency losses. The oscillator for the switching regulator controller is fully user-programmable, easing power supply control loop design and allowing the user to maximise regulator performance.