Reference Design for a Powered-Device (PD) Module

Reference Design for a Powered-Device (PD) Module
Maxim > Design Support > Technical Documents > Reference Designs > Hot-Swap and Power Switching Circuits > APP 4162
Keywords: Power-over-Ethernet,PoE,Powered Device,PD,MAX5951,IEEE 802.3af,PWM,pulse-width modulator
REFERENCE DESIGN 4162 INCLUDES: Tested Circuit BOM Board Available Description Test Data Reference Design for a Powered-Device (PD) Module
Based on the MAX5941B PWM Controller
Mar 04, 2008
Abstract: This application note provides a reference design for an IEEE® 802.3af-compliant, 12.95W adjustableoutput powered-device module. Assembled on a 12cm² PCB, the module is based on the MAX5941B PWM
controller and includes hot-swap power switching, a DC-DC converter, and a pair of ORing diode bridges for
compatibility with an external 12V adapter. This article details the performance of the module and provides a
schematic, PCB layout, and components list for the design.
General Description
Page 1 of 11
This application note presents an IEEE 802.3af-compliant, powered-device (PD) module for power-over-Ethernet
(PoE) applications. Based on the MAX5941B PoE interface/PWM controller, this module provides the PD with a
detection signature, a configurable classification signature (optional), programmable undervoltage lockout
(UVLO), and an isolation switch with programmable inrush-current control.
The MAX5941B PD module is assembled on a 12cm² PCB and includes hot-swap power switching, a DC-DC
converter, and a pair of ORing diode bridges for compatibility with an external 12V adapter. In short, it provides
all the functions necessary to implement a DC-DC, fixed-frequency, isolated power supply for PDs, such as IP
phones, wireless access nodes, and security cameras.
Typical Application
The MAX5941B PD module can be used in numerous applications. Figure 1 illustrates a typical application in
which the data outputs from the switch are connected to the inputs of a midspan. The midspan then adds power
to the data on each output that supports PoE.
In this example, port 1 is connected to an Ethernet camera and port 2 is connected to a wireless access point.
When the midspan is switched on (or when the device is connected), the midspan checks each output for a PoE
signature. The module identifies the peripherals on ports 1 and 2 as PoE-enabled devices, and the midspan
supplies both data and power to these peripherals.
The midspan continuously monitors each output to see if a PoE-enabled device has been added or removed.
Since the other ports in this example do not have a PoE signature, the midspan only passes data through to the
connected peripherals.
Figure 1. In a typical application, the data outputs from the switch are connected to a midspan, which adds
power to the data to provide power over Ethernet.
Features
IEEE 802.3af compliant
36V to 60V input voltage range
12V/1A output
No minimum load requirement
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Small SIL package size
Low output ripple and noise
High-efficiency powered device
No external capacitor required
Adjustable output voltage
Low cost
1500V isolation (input to output)
On-board ORing diode used with an external 12V adapter
Pin Description
Figure 2. Pin assignment.
Table 1. Pin Description
Pin
Name Description
Number
1
VA1
Rx Input (1) This input pin is used in conjunction with VA2 and connects to the center tap of
the transformer connected to pins 1 and 2 of the RJ45 connector (Rx)—it is not polarity
sensitive.
2
VA2
Tx Input (2) This input pin is used in conjunction with VA1 and connects to the center tap of
the transformer connected to pins 3 and 6 of the RJ45 connector (Tx)—it is not polarity
sensitive.
3
VB1
Direct Input (1) This input pin is used in conjunction with VB2 and connects to pins 4 and 5 of
the RJ45 connector—it is not polarity sensitive.
4
VB2
Direct Input (2) This input pin is used in conjunction with VB1 and connects to pins 7 and 8 of
the RJ45 connector—it is not polarity sensitive.
5
CP1
Class Programming (1) Connecting an external resistor to CP2 will change the current class
of the module. With no resistor fitted the module will default to Class 0.
6
CP2
Class Programming (2) Connecting an external resistor to CP1 will change the current class
of the module. With no resistor fitted the module will default to Class 0.
7
GND Ground The ground return for the output.
8
VOUT DC Output This pin provides the regulated output voltage from the DC-DC converter.
9
ADJ
Output Adjust The output voltage can be adjusted from its nominal output by connecting an
external resistor from this pin to either the VOUT pin or GND pin.
10
N.C.
No Connection This pin is not connected internally.
Power Classification
Page 3 of 11
Power classification is an optional method for the PD to indicate its power requirements to the power-sourcing
equipment (PSE). The MAX5941B module allows the current class to be externally programmed by connecting a
resistor between the CP1 and CP2 pins, as shown in Figure 3. If no resistor is fitted, the module will default to
Class 0. Table 2 provides a full list of programming resistor values.
Figure 3. To set the power classification, connect a resistor between pins CP1 and CP2.
Table 2. Resistor Values for Programming the Power Class
Class Programming Resistance (Ω) Minimum Power (W) Maximum Power (W)
0
Do not fit
0.44
12.95
1
770
0.44
3.84
2
388
3.84
6.49
3
242
6.49
12.95
4
161
Reserved
Reserved
Output Adjustment
The MAX5941B PD module has an ADJ pin to trim the output voltage up or down from its nominal value. To
adjust the output voltage, connect a resistor between the ADJ pin and either the GND pin or the VOUT pin
(Figure 4). Equations 1 and 2 calculate the resistor values required to achieve the desired trimmed-up and
trimmed-down output voltages.
where VTRIM_UP is the desired trimmed-up output voltage and VTRIM_DOWN is the desired trimmed-down output
voltage.
Figure 4. To adjust the output voltage, connect a resistor between ADJ and GND (trim up) or ADJ and VOUT
(trim down).
Page 4 of 11
Figure 5A. The trimmed-up output voltage curve.
Figure 5. The trimmed-down output voltage curve.
Typical Connections with an External 12V Adapter
Conventionally, the PD is used simultaneously with an adapter, and a diode is connected in series at each
output as shown in Figure 6.
Figure 6. In the conventional solution, the powered device is connected to an adapter, with a diode placed in
series at each output.
For the MAX5941B PD module, the output diode D1 is assembled internally. If the PD is used independently,
replace the diode with a 0Ω resistor to improve efficiency. Figure 7 shows the placement of the ORing diode D1
on the board.
Page 5 of 11
Figure 7. The location of the internal diode D1 on the MAX5941B PD module.
The module only requires one external capacitor, as shown in Figure 8; minimally, a 1µF ceramic capacitor is
recommended.
Figure 8. Typical connection diagram showing the external capacitor connected between GND and VOUT .
Electrical Characteristics
Table 3. Absolute Maximum Ratings
Parameter
Min Typ Max Units
DC Supply Voltage
-0.3 60
V
DC Supply Voltage Surge for 1ms -0.6 80
V
+100 °C
Storage Temperature
-40 Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the module.
These are stress ratings only, and functional operation of the module at these or any other conditions beyond
those indicated is not implied. Exposure to absolute maximum ratings conditions for extended periods may affect
the module's reliability.
Table 4. Recommended Operating Conditions
Parameter
Min Typ Max Units
Input Supply Voltage
36
48
60
V
Undervoltage Lockout
30
36
V
Operating Temperature -40 25
+85 °C
Page 6 of 11
Table 5. DC Electrical Characteristics
Parameter
Min
Nominal Output Voltage (Without the ORing Diode)
11.76 12
12.24 V
Output Current
0
1
A
Output Ripple and Noise
250
mV
Typ Max Units
Efficiency Without the ORing Diode (48V Input, 1A Output) 85
%
Efficiency with the ORing Diode (48V Input, 1A Output)
82
%
Isolation Voltage
1500 V
Waveforms
Figure 9. Output ripple and noise.
Page 7 of 11
Figure 10. Startup and shutdown.
Figure 11. Transient response.
Components List
Page 8 of 11
Table 6. Components List
Designation
Qty Description
C1, C2, C6, C17 4
10µF 25V ceramic capacitor 1206
TDK C3216X5R1E106K
MURATA GRM31CR61E106KA12
C3
1
6800pF 100V ceramic capacitor 0603
TDK C1608X7R2A682K
C4
1
100pF 50V ceramic capacitor 0603
C5, C7, C23
3
0.1µF 50V ceramic capacitor 0603
C9
1
10µF 100V aluminium electrolytic capacitor
SANYO 100CE10FS
C10
1
1000pF 1.5kV ceramic capacitor 1808
TDK C4520X7R3D102K
C12, C25
2
0.1µF 100V ceramic capacitor 1206
TDK C3216X7R2A104K
C13
1
220µF 25V aluminium electrolytic capacitor
SANYO 25CE220FSA
C14
1
1000pF 100V ceramic capacitor 0805
TDK C2012X7R2A102K
C19
1
2.2µF 10V ceramic capacitor 0603
MURATA GRM188R61A225KE34
C22
1
680pF 50V ceramic capacitor 0603
C28
1
4700pF 50V ceramic capacitor 0603
D1, D2
2
Bridge rectifier DIODES HD01-T
D4, D6
2
Diode 200mA 250V SOD323 DIODES BAV21WS
D5, D13
2
60V Schottky rectifier SMA DIODES B360A
D7
1
SMT LED Lamp 0603 FAIRCHILD QTLP600C-Y
D8
1
Transient voltage suppressor DIODES SMAJ54A
R1
1
20Ω ±1% resistor 0603
R5
1
270mΩ ±1% resistor 1206
R9
1
470Ω ±1% resistor 0603
R10
1
10Ω ±1% resistor 1206
R11, R17
2
10kΩ ±1% resistor 0603
R12
1
20kΩ ±1% resistor 0603
R14
1
25.5kΩ ±1% resistor 1206
R15
1
Not used
R16
1
0Ω ±1% resistor 1206
R18
1
1kΩ ±1% resistor 0805
R22
1
9.53kΩ ±1% resistor 0603
R23
1
2.49kΩ ±1% resistor 0603
R24, R31
2
2.5kΩ ±1% resistor 0603
R25, R27
2
1kΩ ±1% resistor 0603
R26
1
4.75kΩ ±1% resistor 0603
R28
1
33kΩ ±1% resistor 0805
Page 9 of 11
R30
1
4.7Ω ±1% resistor 0805
Q1
1
MOSFET 150V SO-8 IR IRF7465TR
U2
1
IC Optocoupler NEC PS2801-1-F4-R-A
U3
1
IC VREF 2.5V 0.4% SOT-23 AAC AZ431AN-A
U5
1
PWM controller for PD MAXIM MAX5941BESE
T1
1
Transformer N P :NS :NB = 35:16:20 L P = 122µH GA3271-AL Coilcraft
Transformer Design
Figure 12. Transformer electrical diagram.
Table 7. Electrical Specifications
Parameter
Conditions
Value
Electrical Strength
50Hz 1 minute, from pins 1–3, 10–12 to pins 5–8
1500V RMS
Primary Inductance
Pins 1, 12; all windings open. Measure at 275kHz
120µH ±10%
Primary Leakage Inductance Pins 1, 12; rest of pins shorted. Measure at 275kHz 3µH (max)
Table 8. Materials
Item Description
1
Core: EFD15, PC40. Manufacturer: TDK
2
Bobbin: EFD15 coil former (SMD), 12 pins
3
Tape: 8.9mm wide insulation tape
4
Magnet wire: 0.25mm diameter with 150°C
5
Magnet wire: 0.27mm diameter with 150°C
6
Magnet wire: 0.10mm diameter with 150°C
7
Varnish
Note All wires include insulation
Figure 13. Transformer building diagram.
Table 9. Transformer Construction
Page 10 of 11
Step
Description
Primary N P1
Start at pin 1. Wind 35 turns of item 4 in approximately 1 layer. Finish on Pin 12
Insulation
Use 1 layer of item 3 for insulation
12V Winding
Start at pins 6 and 5. Wind 16 turns of 2 parallel strands of item 5. Finish at pins 7 and 8
Insulation
Use 1 layer of item 3 for safety insulation
Primary N P2
Start at pin 2. Wind 35 turns of item 4 in approximately 1 layer. Finish on pin 11
Insulation
Use one layer of item 3 for safety insulation
Bias Winding
Start at pin 3. Wind 20 turns of item 6. Spread turns evenly across bobbin. Finish at pin 10
Outer Wrap
Wrap windings with 2 layers of item 3
Final Assembly Assemble and secure core halves. Varnish impregnate with item 9
IEEE is a registered service mark of the Institute of Electrical and Electronics Engineers, Inc.
Related Parts
MAX5941B
IEEE 802.3af-Compliant Power-Over-Ethernet Interface/PWM
Controller for Power Devices
Free Samples More Information
For Technical Support: http://www.maximintegrated.com/support
For Samples: http://www.maximintegrated.com/samples
Other Questions and Comments: http://www.maximintegrated.com/contact
Application Note 4162: http://www.maximintegrated.com/an4162
REFERENCE DESIGN 4162, AN4162, AN 4162, APP4162, Appnote4162, Appnote 4162
Copyright © by Maxim Integrated Products
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