高性能のクラス2の受電機器(PD)をクラス3のデザインにカスタマイズ可能

高性能のクラス2の受電機器(PD)をクラス3のデザインにカスタマイズ可能

著者の連絡先情報

General Description

This reference design is for a highly effcient, fyback 3.3V and 5V Class 2 powered device (PD) that is IEEE 802.3af/at complaint and cost-effective. The reference design can be customized to a 3.3V/2A and 5V/1A Class 3 PD. The design features the MAX5969B and MAX5974A. The MAX5969B controller is fully compliant with the IEEE 802.3af/at standard in a power-over-Ethernet (PoE) system. The device can also get power from a wall adapter (WAD). The MAX5974A provides both control for wide-input-voltage, active-clamped, inductive feedback, current-mode PWM converters and frequency foldback for PoE applications. 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 Class 2 PD or a Class 3 PD.

Specifications:

  • The 3.3V/1A, 5V/0.8A PD is designed to meet the following specifcations:
  • Input voltage: 36V to 57V
  • WAD input voltage: 36V up to 57V (note: the voltage can be 10V to 57V with a dierent transformer.)
  • VOUT1 : 3.3V/1A
  • VOUT2 : 5V/0.8A
  • Output ripples: ±2%
  • Load transient V P-P : ±3% (50% step-load)
  • Line and load regulation: ±2%
  • Total efficiency with load of 1A at 3.3V, 0.8A at 5V, and 48V input: 84.5% (including input LAN transformer and diode bridge)

Top view of the reference design

Top view of the reference design

Bottom view of the reference design

Bottom view of the reference design

Figure 3

Figure 4

Figure 6

Transient Response at 36V Input Voltage:

  • VIN = 36V, IOUT1 = 1A, IOUT2 = 0.4A–0.8A–0.4A
  • Ch1: 100mV/div, 5V output voltage
  • Ch2: 100mV/div, 3.3V output voltage
  • Ch4: 0.5A/div, output current
  • Time base: 400µs/div

Figure 7