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 19
Figure 1. The Pasadena subsystem design block diagram.
Features
IEEE 802.3af/at compliant
Dual output
Tight line regulation
Low ripple
Excellent load transient response
High efficiency
Applications
Security cameras
Wireless access points
Point of sale terminals
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
the PD classification, replace surface-mount (0805) resistor R4.
Table 1
lists the PD classification options.
Page 2 of 19
Table 1. PD Classification Selection
Class
0
1
2
3
4
5
Maximum Power Used by PD
0.44 to 12.95
0.44 to 3.84
3.84 to 6.49
6.49 to 12.95
12.95 to 25.5
> 25.5
Resistor R4 (Ω)
619
118
66.5
43.2
30.9
21.3
Pasadena can also accept power from a WAD. Connect positive and negative WAD power to the WAD+
and WAD- connections, respectively. When WAD power exceeds 44V, WAD power takes precedence over
PSE power. The MAX5969B will internally disconnect VSS from RTN, when switching from PSE power to
WAD power. If WAD power drops below 40V, the MAX5969B will redetect and classify, then provide power
from the PSE through the device's RTN.
Pasadena features two modular RJ45 jacks (J1 and J3) to inter¬face with the Ethernet data signals. J1 is
provided for interfacing the reference design with the Ethernet data signals and PoE power. J3 is provided
to feed data back out of the system. Refer to the RJ45 magnetic jack data sheet on the
Bel Fuse
website
prior to interfacing Pasadena's J1 and J3 modular RJ45 jack with the Ethernet data signals.
Quick Start
Caution: Do not turn on the power supply until all connections are completed.
Required equipment:
IEEE 802.3af/at-compliant PSE and Category 5e Ethernet network cable
-48V, 1A-capable DC power supply, if PSE is not available
Pasadena (MAXREFDES31#) board
Voltmeter
1. Use one of the following methods to power Pasadena:
If network connectivity is required: Connect a Category 5e Ethernet network cable from the
abovementioned PSE to the reference design input port RJ45 connector (J1).
Optionally connect
an additional Category 5e Ethernet network cable to modular RJ45 jack (J3) to gather data that
passes through the Pasadena board.
If network connectivity is not required or unavailable, connect a -48V DC power supply between
the V+ and V- pads on the reference design. Connect the power-supply positive terminal to the
V+ pad and the negative terminal to the V- pad.
2. Connect the positive terminal of the voltmeter to the +3.3V connector at OUT1 of the
MAXREFDES31#.
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3. Connect the negative terminal of the voltmeter to the GND connector at OUT1 of the
MAXREFDES31#.
4. Activate the PSE power supply or turn on the external DC power supply.
5. Using a voltmeter, verify that MAXREFDES31# provides +3.3V across the +3.3V and GND
connections at OUT1. GND is galvanically isolated from the EV kit's input VDD and WAD pads.
6. Repeat steps 2 and 3, connecting the voltmeter to the +5V and GND terminals of OUT2 to verify that
MAXREFDES31# provides +5V across the connections at OUT2.
Lab Measurements
Equipment used:
Multimeter (Fluke 189 or equivalent)
MAX5971AEVKIT (power source equipment
KGU Unit)
®
Oscilloscope (Tektronix TDS3034B or equivalent)
Current probe (Tektronix TCP202 or equivalent)
Voltage probe (Tektronix Tek6193A or equivalent)
Two each BK Precision 8540 electronic load or equivalent
One each
8-Port 1Gbps workgroup Ethernet switch
(Netgear GS608 or equivalent)
®
Two each PCs with Windows XP and a
1Gbps full-duplex Ethernet network interface card (NIC).
Take special care and use proper equipment when testing the Pasadena design. Any high-power design
involves risk and the necessary safety precautions must be taken. Duplication of the presented test data
requires a low-distortion signal source.
®
Efficiency and Regulation
Figure 2
shows the efficiency of the DC-DC circuit, after the diode bridges, with varying output power, for
three different input voltages of 40V, 48V, and 57V.
Table 2
shows the efficiency of each rail at full current,
while the other rail is at 0A.
Table 3
shows line regulation, each data point is the difference of the output
voltages while the input voltage is swept from 40V to 57V.
Table 4
shows the load regulation, each data
point is the difference in output voltage from 0A to max current. Points are shown for the other rail at both
0A and max current.
Table 5
shows cross regulation, each data point is the difference in output voltage
represented by the equation below.
Cross regulation = V
OUT
(3.3V = 0A, 5V = 3A) – V
OUT
(3.3V = 1.8A, 5V = 0A)
Figures 3–14
show transient response of 3.3V and 5V outputs when stepped from 100% to 50% to 100%.
Figures are shown for input voltages of 40V, 48V, and 57V, and secondary rail outputs of 0A and maximum
current.
Page 4 of 19
Figure 2. DC-DC efficiency of the Pasadena design, following the diode bridges.
Table 2. DC-DC Efficiency
Input voltage
40V
48V
57V
DC-DC Efficiency
(3.3V = 1.8A, 5V = 0A)
90.41%
88.97%
87.20%
DC-DC Efficiency
(3.3V = 0A, 5V = 3A)
89.80%
90.19%
90.00%
DC-DC Efficiency
(3.3V = 1.8A, 5V = 3A)
89.09%
89.80%
90.28%
Table 3. Line Regulation with Input Voltage Swept from 40V to 57V at No Load and Max Load
Conditions
Input
40V to 57V
40V to 57V
Load
0W
20.94W
3.3V
-12.7mV (-0.38%)
-5.5mV (-0.17)
5V
20mV (0.40%)
1.8mV (0.04%)
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