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Maxim > Design support > App notes > Basestations/Wireless Infrastructure > APP 5043
Maxim > Design support > App notes > Hot-Swap and Power Switching Circuits > APP 5043
Maxim > Design support > App notes > Power-Supply Circuits > APP 5043
Keywords: powered device, PD, Power over Ethernet, PoE, IEEE 802.3af, IEEE 802.3at, Class 2 PD, Class 3 PD, IP phones, IP
cameras, security camera, WAP, Wireless Access Point, Point of Sales, POS, Thin Client, Ethernet repeater, active clamped forward,
flyback
Apr 28, 2011
REFERENCE DESIGN 5043 INCLUDES:
Tested circuit Schematic BOM
Active-Clamped Forward, Dual-Output PD Provides High-Performance
Solution for PoE Applications
Abstract: This reference design is for a highly efficient, active-clamped forward, dual 3.3V/8.8V-
output powered device (PD). The design features the MAX5969A and MAX5900 as its
controllers. The design also uses the MAX5974C, which controls current-mode PWM converters
and provides zero-voltage switching (ZVS) and frequency foldback to enhance supply efficiency.
Using these devices, this RD is IEEE® 802.3at compliant and is a high-performance, compact,
and cost-efficient solution for PoE and nonstandard high-power PDs. The design can also
support the auxiliary input voltage to provide maximum 55W output power.
General Description
The design features the MAX5969A, MAX5900, and MAX5974C. The MAX5969A is compliant
with the IEEE 802.3at standard in a power-over-Ethernet (PoE) system. The device can also get
power from a wall adapter (WAD). The MAX5900 hot-swap controller smoothly enables a
nonstandard high power from a nonstandard Power Sourcing Equipment (PSE). The MAX5974C
provides control for wide-input-voltage, ZVS active-clamped, current-mode PWM converters and
frequency foldback for PoE and high-power applications. Using these devices, this reference
design is IEEE 802.3at compliant. It is also a high-performance, compact, and cost-effective
solution for a nonstandard high power PD.
Specifications
The 3.3V/3.35A and 8.8V/4.6A PD is designed to meet the following specifications:
Input voltage: 42V to 57V
Nonstandard PSE: 37V to 57V
WAD input voltage: 30V up to 57V
V
OUT1
: 3.3V/3.35A
V
OUT2
: 8.8V/4.6A
Output ripples: ±1%
Line and load regulation: 3.3V = ±0.2%, 8.8V = ±2%
Total efficiency with loads of 3A at 3.3V, 4.2A at 8.8V, and 48V input: 90.4% (including input LAN transformer and MOSFET
bridge)
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