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Analog Devices Inc. LT4276CIUFD#PBF
- Part No.:
- LT4276CIUFD#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- Power Over Ethernet (PoE) Controllers
- Package:
- 28-WFQFN Exposed Pad
- Datasheet:
-
LT4276CIUFD#PBF.pdf
- Description:
- IC POE CNTRL 1 CHANNEL 28QFN
- Quantity:
- Payment:
- Shipping:
Inventory:433
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Product details
Overview
LT4276CIUFD#PBF from Analog Devices (formerly Linear Technology) is a IEEE 802.3af-compliant Powered Device (PD) controller for PoE applications, supporting up to 13W Type 1 power delivery. It integrates a forward/flyback switching regulator controller with external N-channel Hot Swap MOSFET drive, auxiliary supply sensing via AUX pin, and 3.17V feedback reference. Used in low-power PoE endpoints such as VoIP phones and IoT sensors.
For engineers reviewing the LT4276CIUFD#PBF datasheet, LT4276CIUFD#PBF pinout, LT4276CIUFD#PBF application, or LT4276CIUFD#PBF equivalent, key selection criteria include its 13W IEEE 802.3af compliance, 28-lead 4mm × 5mm QFN package, –40°C to 85°C operating range, flyback/forward topology configurability, and auxiliary power override capability down to 9V.
Technical Context
The LT4276CIUFD#PBF implements IEEE 802.3af detection, classification, and maintain-power-signature functions with a 23.6–25.5kΩ signature resistance and 12.5–21V classification voltage range. Its current-mode switching regulator supports both flyback (no opto-isolator required) and forward topologies via FFSDLY pin configuration, with programmable switching frequency (200–320kHz) and 3.17V FB31 regulation voltage.
It features an inverted ITHB pin (3.17V offset, –40µA/V transconductance), duty-cycle-based soft-start, internal buck controller for VCC generation, and auxiliary supply sensing with 6.05–6.45V threshold and hysteresis. The device uses external N-channel MOSFETs for Hot Swap control, enabling >94% end-to-end efficiency when paired with LT4321 ideal bridge.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| IEEE Standard | Compliant with IEEE 802.3af only (13W Type 1 PD); not LTPoE++ or 802.3at capable. |
| Max Delivered Power | 13W at RJ45 connector; requires RCLASS = 52.3Ω for Class 3 classification. |
| Operating Temp Range | –40°C to +85°C (Industrial grade, IUFD package variant). |
| Package | 28-lead 4mm × 5mm plastic QFN with exposed thermal pad (Pin 29 = GND). |
| FB31 Regulation Voltage | 3.17V ±6mV; enables precise output voltage setting without opto-isolator in flyback mode. |
| VPORT Operating Range | 60V max input; 35–37V hot-swap turn-on threshold ensures reliable PSE handshaking. |
| Switching Frequency | 200–320kHz (ROSC pin programmable); default 214kHz with ROSC open. |
| Overcurrent Threshold | 140mV (typ) across ISEN+–ISEN–; sets peak current limit for external power FETs. |
Pinout & Package
LT4276CIUFD#PBF is housed in a 28-lead 4mm × 5mm plastic QFN (UFD) package with exposed thermal pad (Pin 29) that must be soldered to PCB GND for thermal and electrical integrity. Pin 27 (NC) and Pin 3 (RCLASS++) are not connected; Pin 5 (T2P) is unconnected per datasheet - unused in LT4276C variant.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| GND (Pins 1, 19, 29) | Device ground reference and thermal path | Exposed pad (Pin 29) must be electrically and thermally tied to PCB GND plane. |
| AUX (Pin 2) | Auxiliary supply sense input | Sinks 3.3–7.3µA below 6.05–6.45V threshold; enables auxiliary power takeover and disables classification. |
| RCLASS (Pin 4) | IEEE 802.3af classification resistor input | Accepts 1% resistor to GND (e.g., 52.3Ω for 13W Class 3); defines PD power class. |
| FFSDLY (Pin 12) | Flyback/forward topology select & gate delay control | Pull to GND for flyback (tPGDELAY ≈ 2.69ns/kΩ × R + 30ns); pull to VCC for forward mode. |
| ITHB (Pin 13) | Inverted current threshold control | 3.17V offset; negative gain (–40µA/V) maps voltage to peak current sense comparator threshold. |
| FB31 (Pin 14) | Flyback third-winding feedback input | 3.17V reference enables isolated output regulation without opto-isolator; connect to GND in forward mode. |
| ISEN+/ISEN– (Pins 16–17) | Differential current sense inputs | Measure voltage drop across external sense resistor; 140mV threshold triggers overcurrent fault. |
| PG/SG (Pins 20, 18) | Primary/secondary gate drive outputs | PG drives primary-side FET; SG drives synchronous rectifier (flyback) or active clamp (forward). |
| HSGATE/HSSRC/VPORT (Pins 26, 25, 28) | Hot Swap MOSFET gate/source/drain interface | Supports external N-channel MOSFET; enables low-RDS(ON), high-efficiency inrush control. |
Key Features
| Feature | Design Value |
|---|---|
| IEEE 802.3af Type 1 PD compliance | Guarantees interoperability with legacy PoE infrastructure delivering up to 13W. |
| Configurable flyback or forward topology | Single IC supports both isolated topologies via FFSDLY pin bias - no redesign needed. |
| No-opto flyback feedback | 3.17V FB31 reference and fixed-interval sampling eliminate opto-isolator, improving reliability and transient response. |
| External N-channel Hot Swap MOSFET drive | Reduces conduction loss vs. P-channel; enables >94% system efficiency with LT4321 ideal bridge. |
| Auxiliary supply override | AUX pin senses auxiliary input ≥9V and seamlessly transitions power source while disabling PoE classification. |
| Robust surge protection | 100V absolute maximum rating on VPORT/HSSRC/VIN pins withstands PoE line transients. |
Applications
| VoIP Phones | IoT Edge Sensors |
|---|---|
|
Use Scenario: Powered Ethernet endpoint requiring low-noise, regulated DC for audio codec and MCU. IC Role / Device Role / Timing Role: PD controller managing PoE handshaking, Hot Swap inrush control, and isolated 3.3V/5V flyback conversion. Use Value: Eliminates need for separate PoE interface IC and isolated DC/DC converter; reduces BOM count by 2–3 components. |
Use Scenario: Battery-free industrial sensor node powered solely via PoE in harsh environments. IC Role / Device Role / Timing Role: IEEE 802.3af-compliant PD interface with auxiliary supply fallback and wide –40°C to 85°C operation. Use Value: Enables continuous operation during PoE interruption using local 9–57V auxiliary rail - no brownout resets. |
| Smart Building Controllers | Networked Security Sensors |
|
Use Scenario: DIN-rail mounted HVAC controller receiving power and data over single CAT5e cable. IC Role / Device Role / Timing Role: Forward-mode PD controller driving synchronous rectification for high-efficiency 12V output. Use Value: Achieves >92% end-to-end efficiency at full 13W load, reducing thermal stress in enclosed enclosures. |
Use Scenario: Ceiling-mounted motion/light sensor with tamper-proof PoE connection and EMI resilience. IC Role / Device Role / Timing Role: PD controller with 100V-rated VPORT pins and integrated slope compensation for stable current-mode control. Use Value: Withstands lightning-induced surges on long Ethernet runs without external TVS diodes. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar PoE PD controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT4275CIUFD#PBF | Single-event classification only; no T2P pin; lacks LTPoE++/802.3at support; identical 13W af capability and pinout. | Designed for cost-sensitive, non-upgradable PoE endpoints where multi-event signaling is unnecessary. | Select LT4275CIUFD#PBF if only basic 802.3af compliance is required and future PSE upgrade path is not anticipated. |
| MAX5969BETA+ | Integrated Hot Swap MOSFET; fixed 250kHz switching; no AUX pin or flyback/forward selection; 13W 802.3af compliant. | Targeted at space-constrained designs where external FET layout and topology flexibility are secondary to integration. | Choose MAX5969BETA+ when board area is critical and fixed-frequency, integrated-FET operation suffices. |
Compared with LT4276CIUFD#PBF, LT4275CIUFD#PBF offers identical PoE af functionality with reduced feature set and lower cost, while MAX5969BETA+ trades topology flexibility and external FET optimization for monolithic integration and smaller footprint.
Availability
LT4276CIUFD#PBF is available at Aetrix Electronics and suitable for VoIP phones, IoT edge sensors, smart building controllers, and networked security sensors requiring stable component supply and industrial temperature operation.
Supply support for LT4276CIUFD#PBF includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.
Manufacturer
Analog Devices acquired Linear Technology in 2017 and maintains full product support, documentation, and manufacturing continuity for the LT4276 family.
The LT4276 series was designed specifically for high-efficiency, multi-standard PoE Powered Devices - balancing IEEE compliance, topology flexibility, and thermal performance in compact QFN packages.
FAQ
What IEEE standards does the LT4276CIUFD#PBF support?
The LT4276CIUFD#PBF supports IEEE 802.3af (Type 1) only, delivering up to 13W. It does not support 802.3at (PoE+) or LTPoE++ modes. Its RCLASS pin accepts a 52.3Ω resistor for Class 3 (13W) classification, and it implements full detection, classification, and maintain-power-signature per 802.3af Section 33. The LT4276CIUFD#PBF is explicitly excluded from LTPoE++ and 802.3at functionality per datasheet Table "LT4276 Family".
Can the LT4276CIUFD#PBF operate in flyback mode without an opto-isolator?
Yes, the LT4276CIUFD#PBF supports no-opto flyback operation using its FB31 pin and third-winding feedback. The internal amplifier samples FB31 during a fixed 550ns window (tFB) with 3.17V regulation reference, eliminating the need for external opto-couplers. This improves long-term stability and dynamic response. In forward mode, FB31 must be grounded. The LT4276CIUFD#PBF's flyback implementation is validated in Figure 9 and Applications Information Section "Flyback Mode".
What is the function of the AUX pin on the LT4276CIUFD#PBF?
The AUX pin on the LT4276CIUFD#PBF provides auxiliary supply sensing with 6.05–6.45V threshold (VAUXT) and hysteresis. When asserted above VAUXT, it disables classification, disconnects the signature resistor, pulls down HSGATE, and transfers power control to the auxiliary rail. It sinks 3.3–7.3µA (IAUXH) to provide hysteresis. The LT4276CIUFD#PBF supports auxiliary input as low as 9V, making it suitable for hybrid PoE/local power systems.
Is the LT4276CIUFD#PBF pin-compatible with other members of the LT4276 family?
Yes, the LT4276CIUFD#PBF is pin-for-pin compatible with LT4276AIUFD#PBF and LT4276BIUFD#PBF in the same UFD package. However, functional differences exist: RCLASS++ (Pin 3) and T2P (Pin 5) are NC on LT4276CIUFD#PBF, and it only supports 802.3af - not LTPoE++ or 802.3at. Layout reuse is possible, but firmware and external resistor values (e.g., RCLASS = 52.3Ω) must match LT4276C specifications.
What is the purpose of the ITHB pin on the LT4276CIUFD#PBF?
The ITHB pin on the LT4276CIUFD#PBF is an inverted current threshold control input with 3.17V offset voltage (VITHB(OS)) and –40µA/V transconductance. It sets the peak current limit for the external power FET by controlling the current sense comparator threshold (VSENSE). A higher ITHB voltage lowers the effective current limit. This inversion and offset are confirmed in Electrical Characteristics table and Figure 1 of the LT4276CIUFD#PBF datasheet.
LT4276CIUFD#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 28-WFQFN Exposed Pad
- Packaging:
- Tube
- Product Status:
- Active
- Type:
- Controller (PD), DC/DC
- Number of Channels:
- 1
- Power - Max:
- 13 W
- Internal Switch(s):
- No
- Auxiliary Sense:
- Yes
- Standards:
- 802.3af (PoE)
- Voltage - Supply:
- 60V (Max)
- Current - Supply:
- 2mA (Max)
- Operating Temperature:
- -40°C ~ 85°C
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 28-QFN (4x5)
LT4276CIUFD#PBF FAQ
1.How can I place an order for LT4276CIUFD#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT4276CIUFD#PBF on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for LT4276CIUFD#PBF reliable?
The price and inventory of LT4276CIUFD#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT4276CIUFD#PBF is usually 5 days.
3.What payment methods are accepted for LT4276CIUFD#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT4276CIUFD#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT4276CIUFD#PBF?
LT4276CIUFD#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT4276CIUFD#PBF order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for LT4276CIUFD#PBF?
For technical support, including LT4276CIUFD#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT4276CIUFD#PBF requirements.
6.How does Aetrix verify that LT4276CIUFD#PBF is sourced from the original manufacturer or authorized distributors?
All LT4276CIUFD#PBF products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that LT4276CIUFD#PBF meets industry standards.
7.What is the process for return or replacement of LT4276CIUFD#PBF?
All LT4276CIUFD#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT4276CIUFD#PBF, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The LT4276CIUFD#PBF part is unused and in its original packaging.
Return procedure for LT4276CIUFD#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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