SI3402-B-GM - 802.3af PoE PD Controller + DC-DC | Skyworks
MPN: SI3402-B-GM ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $3.95 | $3.95 |
| 10 | $3.62 | $36.20 |
| 100 | $3.1 | $310.00 |
| 500 | $2.74 | $1,370.00 |
| 1,000 | $2.45 | $2,450.00 |
SI3402-B-GM Overview
A PoE PD controller is a specialized power management IC that negotiates power classification with a Power Sourcing Equipment (PSE) over an Ethernet cable (RJ45) and converts the 37-57 V delivered on the spare or signal pairs into a regulated low-voltage rail that downstream point-of-load converters can use. Within the broader system hierarchy, the SI3402-B-GM belongs to the PMIC family -> power management -> wired-connectivity power delivery ICs, and it is the bridge between the Ethernet PHY/magnetics and the host system's main DC-DC converters.
The device features 802.3at (PoE+) and 802.3af (PoE) compatibility, an integrated dual current-limited hotswap switch for inrush control, and a built-in switching regulator controller with on-chip power FET. Its Hot Swap FET and integrated diode bridges eliminate the need for external rectifiers, dramatically shrinking the BOM and PCB footprint. The SI3402-B-GM is the pin-compatible successor to the obsolete SI3402-A, allowing direct PCB layout reuse with only minor component value changes.
Typical applications include IP security cameras, wireless access points, VoIP phones, point-of-sale terminals, IoT gateways, and any Class 0-3 powered device that draws power from the Ethernet cable. Because the SI3402-B-GM integrates surge protection and bridges, it is particularly attractive for outdoor or industrial PoE endpoints where lightning/ESD events are common. The 5x5 mm QFN package provides adequate thermal relief for 13-15W continuous operation when paired with a properly sized copper pour.
When designing with this part, ensure the bulk capacitor across the PoE input meets IEEE 802.3 minimum requirements (typically 100 uF) and that the output inductor is sized for the chosen switching frequency and ripple current. The IC's case temperature must be monitored under full load - derate output power if thermal relief is insufficient.
Drop-in alternatives for SI3402-B-GM — 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-B-GM (same form factor and footprint) — differing in Maximum Output Power, Package, Operating Temperature, Input Voltage Range (PoE), Integrated Diode Bridges.
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 ⚠️ Specs Unverified✓ In Stock
$1.92 / Unit
View Datasheet →SI3400-BZ-GM
✅ Drop-In📋 Reference alternative (not in catalog)
SI3400-E1-GM
✅ Drop-In📋 Reference alternative (not in catalog)
NCP1081
✅ Drop-In📋 Reference alternative (not in catalog)
SI3402-B-GM Maximum Ratings & Electrical Characteristics
| Function | PoE PD Interface + Switching Regulator |
| Standard Compliance | IEEE 802.3af / 802.3at (Type 1) Class 0-3 |
| Maximum Output Power | 15 W (Class 3) / 13 W typical |
| Input Voltage Range (PoE) | 37 V to 57 V |
| Number of Channels | 1 |
| Integrated Hotswap FET | Yes (dual current-limited) |
| Integrated Diode Bridges | Yes (both pairs) |
| Integrated Surge Suppressor | Yes (transient) |
| Switching Regulator | PWM with integrated power FET |
| Package | 20-QFN (5x5 mm) |
| Mounting Type | Surface Mount |
| Operating Temperature | -40C to +85C |
| RoHS Status | Compliant |
| Pin-Compatible Replacement | Si3402-A (obsolete) |
SI3402-B-GM Pin Configuration
| Pin 1 | GND — Ground |
| Pin 2 | VP1 — PoE input pair 1 |
| Pin 3 | VP2 — PoE input pair 2 |
| Pin 4 | VPD — PoE rectified output |
| Pin 5 | VCC — Internal supply rail |
| Pin 6 | CLASS — Class programming resistor |
| Pin 7 | DET — Detection signature |
| Pin 8 | RTN — Return path |
| Pin 9 | GATE — Hotswap gate drive |
| Pin 10 | SW — Switching regulator switch node |
| Pin 11 | BST — Bootstrap |
| Pin 12 | VDD — Regulator driver supply |
| Pin 13 | FB — Switching regulator feedback |
| Pin 14 | COMP — Compensation network |
| Pin 15 | SS — Soft-start |
| Pin 16 | PWRGD — Power good indicator |
| Pin 17 | VOUT — Regulated output voltage |
| Pin 18 | NC — Not connected (per datasheet) |
| Pin 19 | NC — Not connected (per datasheet) |
| Pin 20 | EP — Exposed thermal pad - connect to GND |
Typical Applications
SI3402-B-GM is suitable for 6 applications: IP Security Cameras (Outdoor PoE), Wireless Access Points, VoIP Phones, Point-of-Sale (POS) Terminals, IoT Gateways and Smart Building Sensors, Industrial Ethernet Sensors.
IP Security Cameras (Outdoor PoE)
The SI3402-B-GM powers outdoor PoE IP cameras by accepting 37-57V from the Ethernet cable and delivering a regulated low-voltage rail to the image sensor, SoC, and IR illuminators. Its integrated transient surge suppressor handles line-side ESD events common to outdoor installations, while the on-chip diode bridges eliminate external rectifiers that frequently fail in surge-prone environments. The 15W Class 3 capability easily supports heaters, PTZ motors, and high-resolution IR LEDs. Operating temperature of -40C to +85C covers all outdoor deployment scenarios from arctic cold to desert heat, making it a robust choice for surveillance infrastructure.
Recommended
Wireless Access Points
PoE-powered Wi-Fi access points benefit from the SI3402-B-GM's 15W Class 3 capability and high integration. The chip powers the Wi-Fi SoC, Ethernet PHY, and PA rails directly from the Ethernet cable without needing a separate power brick, simplifying installation on ceilings and outdoor mounts. The low-EMI PWM switching regulator minimizes conducted emissions that could degrade Wi-Fi RF performance, while the integrated hotswap FET manages inrush current during PoE negotiation. Designers can drop the SI3402-B-GM onto a 20-QFN footprint alongside any 2.4/5GHz radio SoC for a compact, single-cable deployment.
Recommended
VoIP Phones
VoIP desk phones are a classic application for the SI3402-B-GM. The IC receives PoE power from the Ethernet switch, negotiates Class 0-3 power allocation, and delivers a clean 5V or 12V rail that powers the handset SoC, LCD display, keypad scanner, and audio codec. The integrated hotswap protection prevents inrush damage during hot-plug events when phones are moved between ports. The compact 20-QFN 5x5 mm package fits within the slim base of enterprise VoIP phones, and the pin-compatible migration path from the obsolete SI3402-A allows existing designs to refresh without PCB rework.
Recommended
Point-of-Sale (POS) Terminals
Retail POS terminals use the SI3402-B-GM to draw power over the Ethernet backhaul, eliminating the need for a dedicated AC adapter at every register and reducing cabling clutter. The 15W power budget covers the main SoC, touchscreen, receipt printer interface, and magnetic-stripe or NFC reader. The integrated surge suppressor protects the terminal from ESD events that occur when cashiers repeatedly connect peripherals. Class 3 power allocation ensures compatibility with standard 802.3af switches already deployed in retail networks, enabling drop-in upgrades from legacy POS systems.
Recommended
IoT Gateways and Smart Building Sensors
Smart-building IoT gateways aggregate data from wireless sensors and forward it to the cloud via Ethernet. The SI3402-B-GM powers the gateway from a single PoE cable, providing up to 15W for the gateway SoC, Ethernet PHY, sub-GHz or BLE radio, and any local actuator relays. Its compact 5x5 mm QFN footprint allows the gateway to fit into ceiling-mounted enclosures, and the integrated surge protection handles switching transients from inductive loads in the building. The pin-compatibility with the Si3402-A allows easy migration for existing gateways that were originally designed around the older IC.
Recommended
Industrial Ethernet Sensors
Industrial sensors and actuators powered by PoE use the SI3402-B-GM to convert the 48V Ethernet supply into the 5V or 24V rails needed by sensor front-ends, microcontrollers, and output drivers. The integrated diode bridges support both signal-pair and spare-pair PoE powering, providing maximum flexibility for legacy cabling. Industrial-grade -40C to +85C operation handles factory-floor temperatures, and the on-chip transient surge suppressor protects sensitive analog front-ends from motor back-EMF and switching noise common in industrial environments. The low-EMI switching regulator ensures the sensor does not inject noise into the Ethernet PHY.
Recommended
Recommended Products Summary
Engineering reference data for SI3402-B-GM — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | SI3402-B-GMR | SI3402-A-GM | SI3400-BZ-GM | NCP1081 |
|---|---|---|---|---|---|
| Package | 20-QFN (5x5 mm) | 20-QFN (5x5 mm) - same | 20-QFN (5x5 mm) - same | 20-QFN (5x5 mm) - same | QFN-20 - same |
| Brand | Skyworks Solutions | Skyworks Solutions - same | Skyworks Solutions - same | Skyworks Solutions - same | onsemi - different |
| Maximum Output Power | 15 W (Class 3) | 15 W (Class 3) | 15 W (Class 3) | Lower (Class 2) | 13 W (Class 3) |
| PoE Standard | 802.3af/at Type 1 | 802.3af/at Type 1 | 802.3af | 802.3af | 802.3af |
| Integrated Diode Bridges | Yes (both pairs) | Yes (both pairs) | Yes | Yes | No (external required) |
| Integrated Surge Suppressor | Yes (transient) | Yes (transient) | Yes | Yes | No (external TVS needed) |
| Lifecycle Status | Active | Active | Obsolete | Active | Active |
| Operating Temperature | -40C to +85C | -40C to +85C | -40C to +85C | -40C to +85C | -40C to +85C |
Key Differentiators
- Highest integration in the Si340x family (vs SI3400-BZ-GM)
- Pin-compatible upgrade path from obsolete part (vs SI3402-A-GM)
- Integrated surge protection (vs NCP1081)
Design Notes
The SI3402-B-GM integrates the switching FET and hotswap switch, so case temperature depends heavily on output power and PCB thermal relief. At 15W continuous output with a typical 80% efficiency, the IC dissipates roughly 3.5W. Estimate: a 5x5 mm QFN with 1 square inch of 2 oz copper pour yields theta_JA around 35 C/W, producing a 123 C junction temperature rise above ambient - acceptable below 25 C ambient but requiring additional copper area or forced airflow at higher temperatures. Always measure case temperature during prototype validation.
Place the bulk input capacitor (100 uF minimum per IEEE 802.3) as close as possible to the VP1/VP2 pins and the exposed thermal pad. The switching regulator output inductor and bootstrap capacitor should be placed within 5 mm of the SW and BST pins to minimize EMI. Use a 4-layer PCB with a dedicated ground plane beneath the SI3402-B-GM to provide both thermal dissipation and EMI shielding. The exposed thermal pad must be soldered to the ground plane with at least 9 thermal vias for adequate heat extraction.
Do not omit the CLASS programming resistor - it sets the negotiated power class with the PSE and an incorrect value will cause the switch to allocate less power than the load requires. The detection signature resistor must be 25 kOhm per IEEE 802.3 specification; deviating from this value causes detection failures and prevents the PSE from powering the device. When migrating from Si3402-A to Si3402-B, review the external inductor and feedback resistor values against the updated datasheet typical application circuit.
Compliance Information
RoHS compliant per Skyworks product page. Industrial-grade -40C to +85C operating range. Not AEC-Q100 qualified - not intended for automotive applications.
