Texas Instruments TPS2377D

Overview

TPS2377D from Texas Instruments is an IEEE 802.3af-compliant Powered Device (PD) controller IC for Power over Ethernet applications. It integrates a 0.58-Ω, 100-V low-side MOSFET switch, fixed 450-mA operational current limit, legacy UVLO thresholds (30.5 V turn-on / 35.1 V turn-off), and programmable inrush current control via ILIM pin. It enables PoE power management in VoIP phones, WLAN access points, and security cameras.

For engineers reviewing the TPS2377D datasheet, TPS2377D pinout, TPS2377D application, or TPS2377D equivalent, key selection considerations include its legacy UVLO behavior (optimized for noncompliant PSEs), open-drain PG reporting, 8-pin SOIC package, and compatibility with Class 3 PD implementations using 357-Ω classification resistor.

Technical Context

The TPS2377D implements detection, classification, and undervoltage lockout functions using internal comparators with hysteresis to transition between IEEE 802.3af states. Its DET pin draws current through a 24.9-kΩ resistor to generate the 25-kΩ incremental resistance signature during detection, while CLASS pin sources classification current (e.g., 28.0 mA typical at 255 Ω) when VDD is between 13 V and 21 V.

It features a true open-drain PG output that asserts high-impedance only after successful classification and RTN voltage stabilization above 10.0 V, with 75–225 µs deglitch timing. The integrated pass device delivers up to 350 mA steady-state current with 0.58-Ω rDS(on) and includes thermal shutdown at 135°C with 20°C hysteresis.

Key Specifications

Pinout & Package

TPS2377D is housed in an 8-pin SOIC (D) package with 1.27-mm pitch, rated for industrial temperature range (−40°C to +85°C) and 100-V absolute maximum rating on VDD, RTN, DET, and PG pins.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar Powered Device controller applications.

Compared with TPS2375D and TPS2376D, the TPS2377D offers fixed legacy UVLO thresholds optimized for interoperability with fielded noncompliant PSEs-making it the preferred choice for retrofit installations where PSE voltage headroom is limited.

Availability

TPS2377D is available at Aetrix Electronics and suitable for VoIP phones, WLAN access points, security cameras, and internet appliances requiring stable component supply across industrial temperature range and long-life PoE deployments.

Supply support for TPS2377D 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

Texas Instruments is a global semiconductor company specializing in analog, embedded processing, and connectivity technologies, with leadership in power management and industrial interface solutions.

The TPS237x family is designed specifically for IEEE 802.3af Power over Ethernet Powered Device control, integrating detection, classification, UVLO, inrush limiting, and power-good signaling into compact 8-pin packages.

FAQ

What is the UVLO behavior of the TPS2377D compared to other devices in the TPS237x family?

The TPS2377D features fixed legacy UVLO thresholds: 30.5 V turn-on and 35.1 V turn-off, with 4.5 V hysteresis. This differs from the TPS2375D (39.3 V / 30.5 V, 8.8 V hysteresis) and TPS2376D (programmable via external divider). The TPS2377D's lower turn-on voltage ensures compatibility with older PSEs that cannot deliver ≥39 V, making it ideal for retrofit installations where the TPS2377D operates reliably despite significant cable voltage drop.

How does the TPS2377D implement inrush current limiting, and what resistor value is recommended?

The TPS2377D uses its ILIM pin to set inrush current via an external resistor to VSS. With R(ILIM) = 178 kΩ, the typical inrush limit is 130 mA. This value is recommended for compatibility with legacy PSEs and avoids triggering their current-limit protection during bulk capacitor charging. The TPS2377D requires this resistor to be connected - leaving ILIM open or shorted to VSS will disable inrush control and risk PSE disconnect.

Can the TPS2377D be used in Class 4 PoE applications?

No, the TPS2377D is designed for IEEE 802.3af (up to Class 3, 12.95 W at PD input) and does not support Class 4 or higher power levels defined in 802.3at/802.3bt. Its fixed 450-mA operational current limit and 100-V pass device rating align with 802.3af specifications. For Class 4 applications, a different controller such as the TPS2375-4 or TPS23861 is required - the TPS2377D cannot be reconfigured to meet Class 4 detection or classification requirements.

What is the function of the N/C pin (Pin 7) on the TPS2377D, and how should it be handled?

Pin 7 on the TPS2377D is designated N/C (No Connection) and is internally unbonded. It must remain unconnected in the PCB layout - neither tied to VSS, VDD, nor left floating with capacitive coupling. Connecting Pin 7 risks unintended internal node interaction or latch-up, as confirmed in TI's official pin description table. The TPS2377D datasheet explicitly states this pin has no electrical function and must be left unconnected to ensure reliable operation.

Does the TPS2377D require external components for detection and classification, and which ones are mandatory?

Yes, the TPS2377D requires three mandatory external components: a 24.9-kΩ ±1% resistor between DET and VDD for detection signature generation; a classification resistor (e.g., 357 Ω for Class 3) between CLASS and VSS; and an ILIM programming resistor (e.g., 178 kΩ) between ILIM and VSS for inrush control. These are not optional - omission of any invalidates IEEE 802.3af compliance. The TPS2377D does not integrate these resistors and relies on precise external values to meet specification limits.