Keywords: Pasadena MAXREFDES31, powered device (PD), power over Ethernet (PoE) SUBSYSTEM BOARD 5840 PASADENA (MAXREFDES31 ): 3.3V AND 5V POE POWERED DEVICE Abstract: Pasadena (MAXREFDES31 ) is a highly efficient, flyback, 3.3V and 5V Class 4 powered device (PD) with a 40V to 57V auxiliary input. The design features the MAX5969B as the controller. The MAX5974A controls current-mode PWM converters and provides frequency foldback for both the auxiliary input and power-over-Ethernet (PoE) applications. The design is a high-performance, compact, IEEE 802.3af/at compliant, cost-efficient solution for a PD with power level up to Class 4. The design can also support the auxiliary-input to provide approximately 21W output power. Introduction The Pasadena (MAXREFDES31 ) reference design features the MAX5969B and MAX5974A (see Figure 1). The MAX5969B controller is fully compliant with the IEEE 802.3af/at standard in a power-over-Ethernet (PoE) system. The device can also be powered from a wall adapter (WAD). The WAD operates with higher priority than PoE, which is controlled by the MAX5969B. The MAX5974A controls a 40V to 57V input- voltage, current-mode PWM converters and provides frequency foldback. Using these devices, this reference design is IEEE 802.3af/at compliant. It is also a high-performance, compact, and cost-effective solution for a PD supporting power up to Class 4 power level. Page 1 of 19Figure 1. The Pasadena subsystem design block diagram. Features Applications IEEE 802.3af/at compliant Dual output Security cameras Tight line regulation Wireless access points Low ripple Point of sale terminals Excellent load transient response High efficiency Detailed Description of Hardware Pasadena interfaces to powered Ethernet with an RJ-45 connector (J1). A second RJ-45 (J3) is present to read data out of the system. The MAX5969B provides the complete interface to the Ethernet connection, providing detection signature, classification signature, inrush current control, and 2-event classification. The MAX5969B also interfaces with a wall adaptor input, detecting the wall adaptor input and switching between power sources. When present, a wall adaptor power source always takes precedence over the power- sourcing equipment (PSE) power, allowing the wall adaptor to power the reference design. The MAX5974A provides up to 21W of galvanically isolated output power with current-mode PWM control using a synchronous-rectified flyback DC-DC converter topology. Both 3.3V and 5V outputs are available. When connected to an IEEE 802.3af/at-compliant PSE, the reference design uses one of the two-channel, full bridge rectifiers to convert the incoming -57V to DC. PCB pads V+ and V- are available for powering the reference design if network-powered PSE is not available. The MAX5969B provides power to the DC-DC circuit at the VDD and RTN pins. Configured for 21W of output power, Pasadena achieves 89.8% (V = IN 48V) efficiency. The surface-mount transformer and optocoupler provide up to 1500V of galvanic isolation. Pasadena is configured for a Class 4 (12.95W to 25.5W) PD classification by resistor R4. To reconfigure lists the PD classification options. the PD classification, replace surface-mount (0805) resistor R4. Table 1 Page 2 of 19