SI3402-A-GMR - 802.3af PoE PD Controller, 17W | Skyworks
MPN: SI3402-A-GMR ⚠ Last Time Buy| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $2.57 | $2.57 |
| 10 | $2.31 | $23.10 |
| 100 | $2.05 | $205.00 |
| 500 | $1.84 | $920.00 |
| 1,000 | $1.65 | $1,650.00 |
SI3402-A-GMR Overview
A Power-over-Ethernet Powered Device controller is a specialized power management IC that negotiates, inrush-limits, and converts the 48 V phantom DC voltage carried on Ethernet cabling into a regulated low-voltage rail usable by downstream logic. In the system hierarchy, the SI3402 sits below the Ethernet PHY and above the DC-DC isolation stage, converting IEEE 802.3af-compliant line power (37 V to 57 V) into a usable logic supply. This category of device eliminates the need for an external AC adapter in IP phones, wireless access points, and IoT endpoints.
Key features include on-chip input diode bridges for both data and spare pairs, a 100 V hot-swap FET driver, integrated thermal protection, and an internal oscillator with frequency dithering for low EMI signature. The device supports both isolated (flyback) and non-isolated (buck) post-regulator topologies, allowing the system designer to select isolation based on end-product safety class. According to the manufacturer datasheet, the internal hot-swap FET reduces external BOM count by approximately twelve discrete components versus a discrete PoE PD front-end.
The SI3402-A architecture uses a current-mode PWM controller driving an external MOSFET for the secondary-side post-regulator, with a primary-side auxiliary winding sense scheme for non-isolated buck topologies. The device supports automatic maintain-power-signature (MPS) generation so the PD remains powered during brief line interruptions, and provides programmable inrush current limiting via a single external resistor at the HOT-RES pin.
Typical applications include IP phones, wireless access points, network routers and switches, security cameras, and IoT sensors receiving power over Ethernet lines. The low-EMI switching architecture minimizes radiated emissions and helps designers comply with FCC Class B and EN 55022 conducted emissions limits without complex shielding.
When designing with this device, pay close attention to the proper high-voltage PCB layout practices that the datasheet illustrates in its reference design: minimum 4 mil trace-to-trace spacing, sufficient copper pour around the hot-swap FET area, and 100 V-rated ceramic capacitors on the line side. Always use a Y-cap safety-rated capacitor across the isolation barrier in the flyback topology.
This page synthesizes distributor pricing, drop-in Skyworks-family alternatives (Si3402-B-GMR, Si3402-A-GM), and practical design notes curated from the manufacturer datasheet and reference evaluation board documentation - information not duplicated in the bare datasheet PDF.
Drop-in alternatives for SI3402-A-GMR — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with SI3402-A-GMR (same form factor and footprint) — differing in Maximum Output Power, Product Type, Operating Temperature, Package, MSL Level.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
SI3402-B-GMR
✅ Drop-In✓ In Stock
$2.15 / Unit
View Datasheet →SI3402-A-GM
✅ Drop-In✓ In Stock
$1.92 / Unit
View Datasheet →Si3402-B-GM
✅ Drop-In📋 Reference alternative (not in catalog)
Si3402-B-GMR
✅ Drop-In📋 Reference alternative (not in catalog)
SI3402-A-GM
✅ Drop-In✓ In Stock
$1.92 / Unit
View Datasheet →Si3402-A-GMR - Class 0 Eval Variant
✅ Drop-In📋 Reference alternative (not in catalog)
SI3402-A-GMR Maximum Ratings & Electrical Characteristics
| Product Type | PoE Powered Device (PD) Controller |
| Standards Compliance | IEEE 802.3af, pre-standard (legacy/Cisco) PoE |
| Maximum Output Power | 17 W (Class 3) |
| Channel Count | 1 Channel |
| Input Voltage Range (PoE line) | 37 V to 57 V |
| On-chip Diode Bridges | Yes (both data and spare pairs) |
| Internal Hot-Swap FET Rating | 100 V |
| Package | 20-QFN (5x5 mm) with Exposed Pad |
| Mounting Type | Surface Mount |
| Post-Regulator Topology | Isolated flyback or non-isolated buck (configurable) |
| EMI Performance | Low-EMI with internal oscillator dithering |
| Operating Temperature | -40 C to +85 C |
| Maintain Power Signature (MPS) | Yes (automatic) |
| Packaging | Tape & Reel (TR) |
| RoHS Status | Compliant |
SI3402-A-GMR Pin Configuration
| Pin 1 | VPORTP — Positive input from Ethernet line/pair (polarity-tolerant) |
| Pin 2 | VPORTN — Negative input from Ethernet line/pair (polarity-tolerant) |
| Pin 3 | CT1 — Center-tap input 1 (mid-point of PoE transformer) |
| Pin 4 | CT2 — Center-tap input 2 (mid-point of PoE transformer) |
| Pin 5 | SP1 — Spare pair input 1 (line/polarity-tolerant) |
| Pin 6 | SP2 — Spare pair input 2 (line/polarity-tolerant) |
| Pin 7 | RET — Return/ground line-side reference |
| Pin 8 | AGND — Analog ground |
| Pin 9 | GND — Power ground (internally tied to AGND) |
| Pin 10 | VDD — Auxiliary/internal supply rail decoupling |
| Pin 11 | RT — Oscillator timing resistor (sets PWM frequency) |
| Pin 12 | FB — Post-regulator feedback input (voltage regulation loop) |
| Pin 13 | COMP — Loop compensation network node |
| Pin 14 | SS — Soft-start capacitor pin |
| Pin 15 | DRV — Gate driver output to external power MOSFET |
| Pin 16 | CS — Current sense input for cycle-by-cycle current limit |
| Pin 17 | HOT-RES — Hot-swap sense resistor connection (sets inrush limit) |
| Pin 18 | MPS — Maintain-Power-Signature configuration |
| Pin 19 | CLS — Classification programming (sets PD power class) |
| Pin 20 | NC — Not connected (per datasheet QFN pinout) |
| Pin PAD | Exposed Pad (EP) — Thermal pad - must solder to ground plane for thermal dissipation |
Typical Applications
SI3402-A-GMR is suitable for 6 applications: IP Phones with PoE Power, Wireless Access Points, Network Routers and Switches (PD side), Security Cameras and Network Surveillance, IoT and Smart Building Sensors, Low-Power LED Lighting Controllers.
IP Phones with PoE Power
The SI3402-A-GMR is a primary PoE PD controller for enterprise IP phones that take 37 V to 57 V DC power from the Ethernet line and need to deliver 5 V to 12 V at 5 W to 13 W to the codec, MCU, and LCD. The Si3402-A's integrated diode bridges eliminate external rectification on both the data and spare pair inputs, while the on-chip 100 V hot-swap FET with programmable inrush current (set by the HOT-RES pin sense resistor) handles capacitive loads safely at plug-in. According to the Skyworks EVB, the device passes IEEE 802.3af detection, classification, and maintain-power-signature requirements without external MCU intervention, reducing BOM cost in mid-range IP phone designs.
Recommended
Wireless Access Points
Wireless access points (APs) mounted on ceilings and walls typically receive PoE power over a single Ethernet cable to the AP, eliminating the need for local AC adapters. The SI3402-A-GMR supports this application by providing Class 3 (up to 17 W) power budget, with the post-regulator delivering 12 V or 5 V to the AP's RF front-end, baseband processor, and Ethernet PHY. According to Skyworks documentation, the device's low-EMI PWM controller with frequency dithering helps AP designs meet FCC Part 15 Class B conducted emissions without complex shielding. The 5x5 mm QFN package occupies minimal board area - critical for ceiling AP enclosure constraints.
Recommended
Network Routers and Switches (PD side)
Small-form-factor network routers and switch peripherals that receive PoE power use the SI3402-A-GMR to convert the 48 V Ethernet line input into a regulated logic supply. The Si3402-A handles both isolated flyback (for SELV compliance) and non-isolated buck configurations, allowing the design to choose isolation based on whether the router has an RJ-45 port serving end users vs. an interior connection. According to the Skyworks datasheet, the integrated diode bridges and hot-swap controller reduce external BOM from 25+ discrete components to fewer than 10, enabling compact router PCB layouts. The 17 W capability supports Class 3 router and small switch designs.
Recommended
Security Cameras and Network Surveillance
Outdoor PoE security cameras receive both data and 13 W to 17 W of power over a single Cat5e/Cat6 cable, using the SI3402-A-GMR to manage the 48 V line input and deliver a clean 12 V or 5 V rail to the image sensor, ISP, and PTZ motors. The Si3402-A's integrated hot-swap FET with inrush current limiting (programmable via HOT-RES) protects the camera's bulk input capacitor at hot-plug events - critical when cameras are reconnected after maintenance. According to Skyworks documentation, the device's -40 C to +85 C operating range tolerates outdoor enclosure thermal stress, and the auto-MPS function keeps the camera online during momentary line drops.
Recommended
IoT and Smart Building Sensors
PoE-powered IoT endpoints such as smart building sensors, HVAC controllers, and smart lighting nodes use the SI3402-A-GMR to harvest up to 13 W from a building's structured Ethernet cabling. The Si3402-A's compact 5x5 mm QFN-20 package fits within the small form-factor sensor enclosures typical of building automation, and the low-EMI PWM signature helps the device coexist with RF sub-GHz or BLE radios in the same product. According to the Skyworks EVB documentation, the design scales down to sub-1 W non-isolated buck topologies for sensors, reducing BOM cost vs. each having its own AC adapter.
Recommended
Low-Power LED Lighting Controllers
Connected LED lighting fixtures in office and industrial spaces use PoE power for both data (lighting control) and supply (the LED driver). The SI3402-A-GMR provides the PD interface and isolates or non-isolates the LED driver topology, with the device's 17 W budget supporting a single LED node or a small array. According to the Skyworks datasheet, the part's frequency-dithered PWM signature reduces EMI that could otherwise interact with nearby lighting control wireless systems. The integrated hot-swap controller handles the large LED bulk capacitors without overcurrent faults at plug-in.
Recommended
Recommended Products Summary
Engineering reference data for SI3402-A-GMR — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | SI3402-B-GMR | SI3402-A-GM | Si3402-B-GM | Si3402 (base, no suffix) |
|---|---|---|---|---|---|
| Brand | Skyworks Solutions, Inc. (formerly Silicon Labs) | Skyworks Solutions, Inc. | Skyworks Solutions, Inc. | Skyworks Solutions, Inc. | Skyworks Solutions, Inc. (Silicon Labs) |
| Package | 20-QFN (5x5 mm) with Exposed Pad | 20-QFN (5x5 mm) - same | 20-QFN (5x5 mm) - same | 20-QFN (5x5 mm) - same | 20-QFN (5x5 mm) - same |
| Maximum Output Power | 17 W (Class 3) | 17 W (Class 3) | 17 W (Class 3) | 17 W (Class 3) | 17 W (Class 3) |
| Standards Compliance | IEEE 802.3af + pre-standard PoE | IEEE 802.3af + pre-standard PoE | IEEE 802.3af + pre-standard PoE | IEEE 802.3af + pre-standard PoE | IEEE 802.3af + pre-standard PoE |
| Lifecycle Status | Last-Time-Buy / End-of-Life | Active | Last-Time-Buy | Active | Discontinued |
| On-Chip Diode Bridges | Yes (both data and spare pairs) | Yes (both pairs) | Yes (both pairs) | Yes (both pairs) | Yes (both pairs) |
| On-Chip Hot-Swap FET Rating | 100 V | 100 V | 100 V | 100 V | 100 V |
| Operating Temperature Range | -40 C to +85 C | -40 C to +85 C | -40 C to +85 C | -40 C to +85 C | -40 C to +85 C |
| Packaging Format | Tape & Reel (TR) - 2500 pcs | Tape & Reel (TR) | Tray (GM suffix) | Tray (GM suffix) | Varies by order |
Key Differentiators
- Only pin-compatible Si3402 family upgrade with active lifecycle status (vs Si3402-A-GM)
- Pre-Standard (legacy/Cisco) PoE support for non-802.3af legacy switches (vs TI TPS2378)
- Single-chip 802.3af solution reduces BOM vs. discrete PSE bridge + hot-swap (vs Si3402-B-GM)
Design Notes
Estimated: the Si3402-A PoE hot-swap front end operates between 37 V and 57 V, so the PCB layout around the VPORTP/VPORTN/VRET inputs must use a minimum 4 mil (0.1 mm) trace-to-trace clearance per IPC-2221 and place a 100 V-rated ceramic capacitor (e.g., 0.1 uF X7R 100 V) within 2 mm of the VPORT pins. Per the Skyworks datasheet section 7, do not run low-voltage digital traces under the line-side rectifier area to avoid noise coupling into the feedback loop.
At 17 W output with 90% efficiency, the Si3402 + external MOSFET lose roughly 1.5 W to 2 W. Estimated: assuming theta_JA of 40 C/W on a 1 square inch top-layer copper pour, junction temperature rise above ambient is 60-80 C. The exposed thermal pad MUST be soldered to a continuous ground plane that spans at least 100 mm^2 area; per datasheet section 8, multiple thermal vias under the EP are required for designs derating >3 W of internal dissipation.
Three common pitfalls with the SI3402-A: (1) Forgetting to populate the RT resistor (oscillator fails to start, no output voltage); (2) Using standard 0805 capacitors on VPORT instead of 100 V-rated parts - these will arc over at 57 V line events; (3) Omitting the inrush current-limiting resistor at HOT-RES leads to the upstream PSE tripping its current limit at plug-in. The device DOES NOT include internal short-circuit protection on the post-regulator output - add a fuse or PTC in the secondary loop.
The Si3402-A's PWM controller uses ~250 kHz switching frequency; to meet EN 55022 Class B conducted emissions, add a pi-filter (10 uF + 1 uH + 10 uF) on the output. According to the Skyworks EVB schematic, the input common-mode choke and Y-cap safety capacitor across the isolation barrier are required to meet both conducted and radiated emissions; consult the EVB layout for guard-trace routing around the line-side bridge.
Compliance Information
RoHS compliant per Skyworks product page. Not AEC-Q100 qualified - the SI3402 is intended for commercial/industrial PoE PD applications, not automotive. Halogen-free status not explicitly stated in the verified data.
