Silicon Laboratories UG332 User manual

UG332: Class 3 Non-Isolated Evaluation
Board for the Si3406
The Si3406 non-isolated Flyback topology based evaluation board
is a reference design for a power supply in a Power over Ethernet
(PoE) Powered Device (PD) application.
This Si3406-non-ISO-FB EVB maximum output level is Class 3 power (η x 15.4 W).
The Si3406-non-ISO-FB EVB board is shown below. The Si3406 IC integrates an IEEE
802.03at compatible PoE interface as well as a current control based dc/dc converter.
The Si3406 PD integrates two diode bridges, which can be used up to 200 mA input cur-
rent, detection circuit, classification circuit, dc/dc switch, hot-swap switch, TVS overvolt-
age protection, dynamic soft-start circuit, cycle-by-cycle current limit, syncrhonous gate
driver, maintain power signature (MPS), thermal shutdown and inrush current protection.
The switching frequency of the converter is tunable by an external resistor.
KEY FEATURES
• IEEE 802.03at Compatible
• High Efficiency
•High Integration
• Optional MPS Function
• Synchronous Gate Driver
• Low BOM Cost
• Transient Overvoltage Protection
• Thermal Shutdown Protection
• 5x5 mm 20-pin QFN
silabs.com | Building a more connected world. Rev. 0.1

1. Kit Description
The Si3406-non-isolated Flyback topology based evaluation board is a reference design for power supplies in Power over Ethernet
(PoE) Powered Device (PD) applications. The Si3406 device is described more completely in the data sheet and application notes. This
document describes the evaluation board.
The Si3406-non-ISO-FB-C3 EVB board is shown on the cover page. The schematic is shown in Figure 2.3 Si3406-Non-Isolated Fly-
back EVB Schematic: 5 V, Class 3 PD on page 4, and the layout is in 17. Board Layout. The dc output is at connectors J11(+) and
J12(–).
Boards are shipped configured to produce 5 V output voltage but can be configured for different output voltages, such as 3.3 or 12 V,
by changing resistor R14 and a few other components. Refer to “AN1130: Using the Si3406/Si34061/Si34062 PoE+ and Si3404 PoE
PD Controller in Isolated and Non-Isolated Designs” for more information. The preconfigured Class 3 signature can also be modified,
which is described as well in AN1130.
The Si3406 includes integrated diode bridge for both CT and SP connection. The integrated diode bridge can be used up to 200 mA
input current. Above 200 mA input current the external diode bridge is required.
The external diode bridge can be Schottky or silicon type.
The Si3406 device can operate with CT/SP pins open, in this configuration the external bridge should be Schottky type diode bridge.
To compensate the reverse leakage of the Schottky type diode bridges at high temperature, the recommended detection resistor should
be adjusted to the values listed in the following table:
Table 1.1. Recommended Detection Resistor Values
External Diode Bridge RDET
Silicon Type 24.3 kΩ
Schottky Type 24.9 kΩ
UG332: Class 3 Non-Isolated Evaluation Board for the Si3406
Kit Description
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2. Getting Started: Powering Up the Si3406-non-ISO-FB EVB
Ethernet data and power are applied to the board through the RJ45 connector (J1). The board itself has no Ethernet data transmission
functionality, but, as a convenience, the Ethernet transformer secondary-side data is brought out to test points.
The design can be used in Gigabit (10/100/1000) systems as well by using PoE RJ45 Magjack, such as type L8BE-1G1T-BFH from Bel
Fuse.
Power may be applied in the following ways:
• Using an IEEE 802.3-2015-compliant, PoE-capable PSE, such as Trendnet TPE-1020WS
• Using a laboratory power supply unit (PSU):
• Connecting a dc source between blue/white-blue and brown/white-brown of the Ethernet cable (either polarity), (End-span) as
shown below:
Figure 2.1. Endspan Connection using Laboratory Power Supply
• Connecting a dc source between green/white-green and orange/white-orange of the Ethernet cable (either polarity), (Mid-span)
as shown below:
Figure 2.2. Midspan Connection using Laboratory Power Supply
UG332: Class 3 Non-Isolated Evaluation Board for the Si3406
Getting Started: Powering Up the Si3406-non-ISO-FB EVB
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L5
330 Ohm
C6
100uF
R20
47K
J11
D19S1B
TP4 NI
D12S1B
T1
FA2924
29
17 8
10
J12
R14 9.1K
TP9
vss
NI
R21
0
R5
6.8
R15 3.24K
TP5 NI
C16 1nF
NI
R10 48.7
C32
1nF
J1
RJ-45
MX0+ 1
MX0- 3
MX1+ 4
PWR2
8PWR3 9PWR4
10
CT 2
LED_K2 K2 LED_A2 A2 LED_K1 K1 LED_A1 A1
PWR1 7
CT/MX1- 5
MX1- 6
PWR5
11
C10 1uF
Q1
FDMA8051L
TP6 NI
C17 1nF
NI
R13
0.62
C20
1nF
C9 100uF
NI
C12 1nF
NI
C4
0.01uF
+ C2
12uF
C13 1nF
NI
TP7 NI
C18 1nF
NI
R8 88.7K
C1
2.2uF
C14 1nF
NI
TP3 NI
C8
0.1uF
TP10
swo
NI
D18S1B
L4
330 Ohm
C5
1nF
+
C7 220uF
D15S1B
TP1
vpos
NI
TP8 NI
TP2
syncl
NI
U1
Si3406
FBH 1
EROUT 2
FBL 3
VDD 4
NSLEEP
5
RDET
6
HSO
7
RCL
8
RFREQ
9
SP2
10
SP1
11
VPOS
12
CT2
13
CT1
14
NT2P 15
SYNCL 16
V11 17
SWO 18
VSS 19
ISNS 20
VNEG
21
L1
330 Ohm
R2
330
R11 24.3k
C19 1nF
NI
D51N4148W NI
C15 1nF
NI
D17S1B
C31
NI
C3
2.2uF
C22
0.1uF
D14S1B
L2
330 Ohm
R1
330
C11 100uF
NI
R4
27k
L3
1uH
TP12
vneg
NI
D4
RS1B
D16S1B
C21
0.22uF
D13S1B
swo
vpos vss
v11
fbl
nt2p
nt2p
vdd
Vss
vout
vss
vpos
vneg
vout
gnds
vdd
vss
vpos erout
isns
vneg
vpos
vpos ct2
ct1
sp2
sp1
vss
vss gnds
Figure 2.3. Si3406-Non-Isolated Flyback EVB Schematic: 5 V, Class 3 PD
UG332: Class 3 Non-Isolated Evaluation Board for the Si3406
Getting Started: Powering Up the Si3406-non-ISO-FB EVB
silabs.com | Building a more connected world. Rev. 0.1 | 4

3. Overall EVB Efficiency
The overall efficiency measurement data of the Si3406-non-ISO-FB EVB board is shown below. The input voltage is 50 V, output volt-
age is 5 V.
Figure 3.1. Si3406-Non-Isolated Flyback Class 3 EVB Overall Efficiency: 50 V Input, 5 V Output, Class 3 PD
Note: The chart shows overall EVB efficiency. The voltage drop on the standard silicon diode bridge is included.
UG332: Class 3 Non-Isolated Evaluation Board for the Si3406
Overall EVB Efficiency
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4. SIFOS PoE Compatibility Test Results
The Si3406-non-ISO-FB EVB board has been successfully tested with PDA-300 Powered Device Analyzer from SIFOS Technologies.
The PDA-300 Powered Device Analyzer is a single-box comprehensive solution for testing IEEE 802.3at PoE Powered Devices (PDs).
Figure 4.1. Si3406-Non-Isolated Flyback C3 PD SIFOS PoE Compatibility Test Results
UG332: Class 3 Non-Isolated Evaluation Board for the Si3406
SIFOS PoE Compatibility Test Results
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5. Feedback Loop Phase and Gain Measurement Results (Bode Plots)
The Si3406 device integrates a current mode controlled switching mode power supply controller circuit. Therefore, the application is a
closed-loop system. To guarantee a stable output voltage of a power supply and to reduce the influence of input supply voltage varia-
tions and load changes on the output voltage, the feedback loop should be stable.
To verify the stability of the loop, the loop gain and loop phase shift has been measured.
-180
-90
0
90
180
-80
-60
-40
-20
0
20
40
60
80
100 1 000 10 000 100 000
Figure 5.1. Si3406-Non-ISOFB-EVB-C3 Measured Loop-Gain and Phase Shift
Table 5.1. Measured Loop Gain and Phase Shift
Frequency Gain Phase
Cursor 1 (Phase Margin) 19.1 kHz 0 dB 78°
Cursor 2 (Gain Margin) 47.1 kHz –7 dB 0 °
UG332: Class 3 Non-Isolated Evaluation Board for the Si3406
Feedback Loop Phase and Gain Measurement Results (Bode Plots)
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6. Step Load Transient Measurement Results
The Si3406-non-ISO-FB EVB board's output has been tested with a step load function to verify the converters output dynamic re-
sponse.
Figure 6.1. Si3406-Non-Isolated Flyback EVB PD Output Step Load Transient Test
UG332: Class 3 Non-Isolated Evaluation Board for the Si3406
Step Load Transient Measurement Results
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7. Output Voltage Ripple
The Si3406-non-ISO-FB output voltage ripple has been measured in both no load and heavy load conditions.
Figure 7.1. Si3406-Non-Isolated Flyback C3 EVB Output Voltage Ripple No Load (Left) and Heavy Load (Right) Conditions
UG332: Class 3 Non-Isolated Evaluation Board for the Si3406
Output Voltage Ripple
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8. Soft Start Protection
The Si3406 device has an integrated dynamic soft-start protection mechanism to avoid stressing the components by the sudden current
or voltage changes associated with the initial charging of the output capacitors.
Figure 8.1. Si3406-Non-Isolated Flyback C3 EVB Input Current and Output Voltage Soft-Start at Low Load (Left) and Heavy
Load (Right) Conditions
UG332: Class 3 Non-Isolated Evaluation Board for the Si3406
Soft Start Protection
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9. Output Short Protection
The Si3406 device has an integrated output short protection mechanism, which protects the IC itself and the surrounding external com-
ponents from overheating in the case of electrical short on the output.
Figure 9.1. Si3406-Non-Isolated Flyback C3 EVB Output Voltage and Input Current when Output is Shorted
UG332: Class 3 Non-Isolated Evaluation Board for the Si3406
Output Short Protection
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10. Pulse Skipping at No-Load Condition
The Si3406 device has an integrated pulse skipping mechanism to ensure ultra-low power consumption at no load condition.
Figure 10.1. Si3406 Pulse Skipping at No-load Condition: SWO Waveform
UG332: Class 3 Non-Isolated Evaluation Board for the Si3406
Pulse Skipping at No-Load Condition
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11. Adjustable EVB Current Limit
For additional safety, the Si3406 has an adjustable EVB current limit feature. The EVB current limit through the ISNS pin measures the
voltage on RSENSE. When VRSENSE = -270 mV (referenced to Vss), the current limit circuit restarts the circuit to protect the application.
The EVB current limit for this Class 3 application can be calculated with the following formula:
RSENSE = 0.62Ω
ILIMIT =270mV
0.62Ω= 435mA
Equation 1. EVB Current Limit
UG332: Class 3 Non-Isolated Evaluation Board for the Si3406
Adjustable EVB Current Limit
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12. Tunable Switching Frequency
The switching frequency of the oscillator is selected by choosing an external resistor (RFREQ) connected between the RFREQ and
VPOS pins. The following figure will aid in choosing the RFREQ value to achieve the desired switching frequency.
Figure 12.1. Switching Frequency vs RFREQ
The selected switching frequency for this application is 220 kHz, which is achieved by setting the RFREQ resistor to 88.7 kΩ.
UG332: Class 3 Non-Isolated Evaluation Board for the Si3406
Tunable Switching Frequency
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13. Synchronous Rectification
The Si3406 device has synchronous gate driver (SYNCL) to drive the rectifier MOSFET. At low-load the converter works in discontinu-
ous current mode (DCM); at heavy load, the converter runs in continuous current mode (CCM). At low-load the SWO voltage waveform
has a ringing waveform, which is typical for a DCM operation.
Figure 13.1. SWO and SYNCL Voltage Waveforms at Discontinuous Current Mode (DCM) (Left) and in Continuous Current
Mode (CCM) (Right)
The device operates in non-synchronous mode at light load (IIN < 25 mA). As the input current increases, Si3406 automatically changes
its switching operation from "Non-Synchronous" to "Synchronous". The dynamic operation adjustment maximizes overall power efficien-
cy.
UG332: Class 3 Non-Isolated Evaluation Board for the Si3406
Synchronous Rectification
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14. Maintain Power Signature
The Si3406 device integrates an MPS circuit which ensures connection with the PSE if the PD application current drops below PSE
threshold level.
There are two modes of MPS operation:
• Automatic mode MPS (consumption-based)
• User mode MPS
Automatic Mode MPS (Consumptions Based):
If nSLEEP is low at startup, MPS generation depends on chip current consumption:
• MPS pulses are enabled below a certain level of total PD current consumption to ensure connection with the PSE
• MPS pulses are disabled above a certain level of total PD current consumption not to degrade overall board efficiency
nSLEEP = low
IIN
Figure 14.1. Automatic MPS Mode, nSLEEP is Low; MPS is Enabled when PD Consumption is Low; MPS is Disabled when PD
Consumption is Higher
User Mode MPS:
If nSLEEP is high at startup, MPS generation depends on nSLEEP.
• if nSLEEP is high, MPS disabled (independently of the current consumption)
• if nSLEEP is low, MPS enabled (independently of the current consumption)
nSLEEP = high
IIN
nSLEEP = low
At startup, nSLEEP was high
Figure 14.2. With nSLEEP High, MPS is Disabled (Left); with nSLEEP Low, MPS is Enabled (Right); MPS
Generation is Fully Controlled by the User
UG332: Class 3 Non-Isolated Evaluation Board for the Si3406
Maintain Power Signature
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15. Radiated Emissions Measurement Results
Radiated emissions have been measured of the Si3406-non-ISO-FB EVB board with 50 V input voltage and full load connected to the
output – 12.5 W.
As shown below, the Si3406-non-ISO-FB EVB is fully compliant with the international EN 55022 class B emissions standard.
Figure 15.1. Si3406-Non-Isolated Flyback EVB Radiated Emissions Measurement Results; 50 V Input, 5 V Output, 12.5 W Out-
put Load
15.1 Radiated EMI Measurement Process
The EVB is measured at full load with peak detection in both vertical and horizontal polarizations. This is a relatively fast process that
produces a red curve (vertical polarization) and a blue curve (horizontal polarization). Next, specific frequencies are selected (red stars)
for quasi-peak measurements. The board is measured again at those specific frequencies with a quasi-peak detector, which is a very
slow but accurate measurement. The results of this quasi-peak detector measurement are the blue rhombuses.
The blue rhombuses represent the final result of the measurement process. To have passing results, the blue rhombuses should be
below the highlighted EN 55022 Class B limit.
UG332: Class 3 Non-Isolated Evaluation Board for the Si3406
Radiated Emissions Measurement Results
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16. Conducted Emissions Measurement Results
The Si3406-non-ISO-FB EVB board's conducted emissions have been measured, the result is shown below.
Figure 16.1. Si3406-Non-Isolated Flyback EVB Conducted Emissions Measurements Results; 50 V Input, 5 V Output, 12.5 W
Output Load
UG332: Class 3 Non-Isolated Evaluation Board for the Si3406
Conducted Emissions Measurement Results
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17. Board Layout
Figure 17.1. Top Silkscreen
Figure 17.2. Top Layer
UG332: Class 3 Non-Isolated Evaluation Board for the Si3406
Board Layout
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Figure 17.3. Internal 1 (Layer 2)
Figure 17.4. Internal 2 (Layer 3)
UG332: Class 3 Non-Isolated Evaluation Board for the Si3406
Board Layout
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