Design And Research Based On Power Device Controller Chips In Power Over Ethernet

Power over Ethernet (PoE) describes a standardized system to pass electrical power along with data on Ethernet cabling, which saves space and cost in application, as well as making devices easy to manage. Therefore, PoE is widely used in IP phone, wireless AP, video surveillance and building management. This paper focuses on the development of chips for Power Device (PD) in PoE system and proposes unique solution to the difficulties in the chip design.According to the standard of IEEE802.3af, a circuit structure for PD controller is proposed. This circuit structure is constituted of interface chip and power management chip. Interface chip is in charge of communication with power supply device (PSE), while power management chip can convert the power from PSE to terminal device.Voltage reference, as a frequently used modules in analog circuits, is dispensable in PD controller chips. This paper studies the design of high performance voltage reference. Schemes for low-temperature-drift voltage reference and high-power-supply-rejection (high-PSR) voltage reference are presented. A high order temperature compensation for low-temperature-drift voltage reference is proposed, which uses a4-input differential amplifier to add the high-order temperature item to a1st-order-compensated bandgap reference, generating a reference of a much slower temperature coefficient (TC). A negative feedback loop is involved in the high-PSR voltage reference to regulate the supply voltage of the core bandgap reference, which suppresses the power supply noise of the reference. Both chips are designed in TSMC0.35μm CMOS technology. Measurement results show the TC of low-temperature-drift voltage reference is only2.1ppm/℃ranging from-40to125℃, and the PSR for high-PSR voltage reference is-120dB@DC and-80dB@10kHz.The presented interface chip can provide function of detection, classification, inrush current limit and disconnection. Current comparator is used to detect voltage for detection which minimizes the chip area as well as the detection time. High precision comparator is used to monitor the voltage signal over the sensing resistor in current-limit, which can guarantee the accuracy of current-limit and minimize the power consumption. The PD interface chip is designed in CSMC0.5μm BCD technology. Measurement results show the chip can accomplish the whole function of detection, classification, inrush current limit and disconnection.Power Device works under the high voltage of48V, providing a power of greater than12.95W, so a high-voltage high-reliability fly-back controller with peak current mode is proposed. The controller utilizes a novel fault protection circuit to monitor the output of error amplifier and peak current, which makes the fault detection much faster, keeping the system safe. The fly-back controller is designed in CSMC0.5μm BCD technology. Measurement results show the chip can quickly start whenever a fault occurs, preventing damage to the converter and reducing system losses. The converter can recover by itself when the fault is removed. The fly-back converter works over the voltage range from34to60V. The load regulation is1.32mV/A, the line regulation is1.05mV/V, and the maximum efficiency is83.5%.The floating buck converter uses NMOS as the switching device and doesn’t require a boot-strapped circuit to boost driving signal, which lowers application cost and increases the fields of PD application. A high-precision voltage translator is involved to make the floating buck converter available. This translator can translate a Vin-referenced feedback voltage to a ground-referenced voltage, which is compared with a normal voltage reference to monitor the output. The translator is non-sensitive to supply voltage and temperature, which makes the translation of high precision. The controller chip of fly-back integrating the voltage translator can be used to driving the floating buck converter. Measurement results show the translator has reached a fixed offset of70mV in translation, which can be corrected by trimming a resistor in the translator. The floating buck converter works over the voltage range from18to60V. The load regulation is10.5mV/A, the line regulation is1.65mV/V and the maximum efficiency is94.5%.The paper finally presents a complete solution for Power Device application compatible with IEEE802.3af. The prototype of Power Device is consisted of the PD interface and the fly-back converter. Measurement results show this Power Device can accomplish detection, classification, inrush current limit and disconnection, providing a power of13W with a maximum efficiency of80.5%.