Si3404 Data Sheet
Fully-Integrated IEEE 802.3 Type 1-Compliant POE PD Interface
and High-Efficiency Switching Regulator with Compact Footprint
The Si3404 integrates the power management and control functions required in a Pow-
er-over-Ethernet (PoE) powered device (PD) application. These devices convert the
high voltage supplied over the 10/100/1000BASE-T Ethernet connection to a regulated,
low-voltage output supply. The optimized architecture of this device minimizes the solu-
tion footprint and external BOM cost and enables the use of low-cost external compo-
nents while maintaining high performance. The Si3404 integrates a transient surge
suppressor. The switching power FET and associated functions are also integrated.
The integrated, current mode controlled switching regulator supports isolated or non-
isolated flyback and buck converter topologies. The switching frequency for the regula-
tor is tunable with a simple external resistor value to help avoid unwanted harmonics
for better emissions control.
This device fully supports the IEEE 802.3at specification for Type 1, single-event classi-
fication. Standard external resistors provide the proper IEEE 802.3 signatures for the
detection function and programming of the classification mode, and internal startup cir-
cuits ensure well-controlled soft-start initial operation of both the hotswap switch and
the voltage regulator.
The Si3404 is available in a low-profile, 20-pin, 4 x 4 mm QFN package.
KEY FEATURES
• Type 1 (PoE) power
• IEEE 802.3at Type 1 compliance
• Current mode dc-dc converter
• Tunable switching frequency
• Transformer bias winding support
• Auxiliary adapter capability
• Integrated hotswap FET and switching FET
• 120 V Absolute Max voltage performance
• Extended –40 to +85 °C temperature
• Compact ROHS-compliant 4 mm x 4 mm
QFN Package
APPLICATIONS
• Voice over IP telephones
• Wireless access points
• Security and surveillance IP cameras
• Point-of-sale terminals
• Internet appliances
• Network devices
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Rev. 1.0
Si3404 Data Sheet
Ordering Guide
1. Ordering Guide
Table 1.1. Si3404 Ordering Guide
Ordering Part Number
Si3404-A-GM
Package
4 x 4 mm 20-QFN
Pb-free, RoHS-compliant
Temperature Range (Ambient)
–40 to 85 °C Extended
Applications
All Purposes
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Table of Contents
1. Ordering Guide
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. System Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 Block Diagram .
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. 4
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4
4
4
5
2.2 Power over Ethernet (PoE) Line-Side Interface
2.2.1 Surge Protection . . . . . . . . .
2.2.2 Telephony Protection . . . . . . .
2.2.3 Detection and Classification . . . . .
2.3 Hotswap Switch
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2.4 HSSW State Machine
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2.5 DC-DC Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.5.1 Average Current Sensing, Overcurrent, Low-Current Detection, and Output Short Protection .
2.6 Tunable Oscillator .
2.7 Regulators .
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2.8 External Wall Adapter Support.
3. Application Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4. Electrical Specifications
5. Pin Descriptions
6. Packaging
. . . . . . . . . . . . . . . . . . . . . . . . . . 11
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.16
5.1 Detailed Pin Descriptions
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.19
.21
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6.1 Package Outline: Si3404
6.2 Land Pattern: Si3404 .
7. Si3404 Top Marking . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
8. Revision History
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
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Rev. 1.0 | 3
Si3404 Data Sheet
System Overview
2. System Overview
The following Block Diagrams will give the designer a sense for the internal arrangement of functional blocks, plus their relationships to
external pins. The Block Diagrams are followed by a description of the features of these integrated circuits.
2.1 Block Diagram
RDET
RFREQ
VT15
VDD
VPOS
250kHz
OSCs
fixed: 250kHz
adjustable: 100...500kHz
AUX
WINDING
SUPPORT
I
BIAS
5V
REGULATOR
THERMAL
PROTECTION
VPOS-1.32V
FBH
FBL
EROUT
VSS+1.32V
DETECTION
TVS
100V
250kHz
PoE
CONTROLLER
THERMAL
PROTECTION
HOT-SWAP
CONTROLLER
Start
CLASS
CURRENT
MODE
PWM
CONTROLLER
DC/DC
SW
SWO
VSS
I
AVG
ISNS
HSO
VNEG
RCL
HSSW
Figure 2.1. Si3404 Block Diagram
2.2 Power over Ethernet (PoE) Line-Side Interface
The PoE line interface consists of external diode bridges, internal surge protection, and protocol interface support for detection and
classification.
The chip features active protection against surge transients and accidentally applied telephony voltages.
2.2.1 Surge Protection
The surge protection circuit is activated if the VPOS-VNEG voltage exceeds V
PROT
and
the hotswap switch is off (dc-dc is not pow-
ered). If the hotswap switch is on, the surge power is sunk in the dc-dc’s input capacitance.
The internal surge protection can be overridden with an external TVS if higher than specified surge conditions need be tolerated. The
external surge device must be connected in parallel to the internal one; therefore, the designer must ensure that the external surge
protection will activate prior to the internal surge protection.
2.2.2 Telephony Protection
The Si3404 provides protection against telephony ringing voltage. The telephony ringing is much longer than the surge pulse but it has
less energy, therefore, the Si3404 has a switch parallel with the supply (between VPOS and VNEG). When the protection circuit is acti-
vated, it turns ON the protection switch; the ringing energy then dissipates on this switch and ringing generator resistance (> 400 Ω).
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Si3404 Data Sheet
System Overview
2.2.3 Detection and Classification
When the Si3404 is connected via Ethernet cable to a PSE-enabled Ethernet switch, it has to provide a characteristic resistance (~25
kΩ) to the PSE in a given voltage range (2.7–10.1 V). This is called detection. After the PSE detects the PD, the PSE increases the
voltage above the classification threshold 14.5 V. Then, the PD provides the classification current to inform the PSE about its required
power class (Class 1, 2, 3, or 4). Type 1 PSEs cannot provide enough power for a Class 4 PD. Type 2 PSEs have additional voltage
steps before switching on the PD. After an initial classification voltage pulse, the Type 2 PSE reduces the voltage below the mark
threshold level (10 V) then raises it up again to the Class event range. Last, before switching ON the dc-dc, it reduces the voltage
again.
The Si3404 is a Type 1 PD. The following figure represents the typical turning ON procedure of the PD, which includes detection, clas-
sification and PD turn ON.
Voltage
57 V
37 V
IEEE 802.3af
startup
37 V - 57 V (af)
20.5 V
14.5 V
10.1 V
2.7 V
Time
Reset
Detection
Classification
PD turned ON
Figure 2.2. Powered Device Voltages
2.3 Hotswap Switch
The hotswap switch is a high voltage switch which separates the PoE inerface from the dc-dc converter domain. The internal hotswap
switch (HSSW) is turned on (conducting) when the PoE interface voltage goes above V
UVLO_R
. It provides limited inrush current until
the dc-dc side capacitor is charged. The hotswap switch turns off (open) if voltage on the HSSW switch is greater than V
HSSW_OFF
.
In overload, the hotswap switch goes into current-limiting mode with a current limit of I
OVL
. It will turn back ON after T
WAITHSSW
elapses
and the dc-dc input capacitor is recharged, meaning the HSO-VNEG voltage is less than V
HSSW_ON
.
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