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Home > Products > Integrated Circuits (ICs) > Power Management (PMIC) > Power Over Ethernet (PoE) Controllers

STMicroelectronics STHS4257A1M6F

Name: STHS4257A1M6F
Brand: STMicroelectronics
SKU: STHS4257A1M6F
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: STHS4257A1M6F

Manufacturer:: STMicroelectronics

Category:: Power Over Ethernet (PoE) Controllers

Package:: 8-SOIC (0.154", 3.90mm Width)

Datasheet:: STHS4257A1M6F.pdf

Description:: IC POE CNTRL 1 CHANNEL 8SO

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Product details

Overview

STHS4257A1M6F from STMicroelectronics is an IEEE 802.3af-compliant Powered Device (PD) interface controller with integrated 100V/450mA low-side MOSFET, 25kΩ signature resistor, resistor-programmable classification (Class 0–4), and open-drain Power Good output - designed for PoE-powered endpoints such as VoIP phones and WLAN access points.

For engineers reviewing the STHS4257A1M6F datasheet, STHS4257A1M6F pinout, STHS4257A1M6F application, or STHS4257A1M6F equivalent, key selection criteria include UVLO thresholds (36.0 V rising / 30.5 V falling), dual-level current limiting (140 mA inrush / 375 mA normal), signature disable capability, thermal protection mode (single-step latch), and SO8 package compatibility.

Technical Context

The STHS4257A1M6F implements a negative-voltage PoE interface where VIN serves as the negative return rail and GND as the positive power rail, enabling polarity-insensitive operation via internal 1.5V offset diodes. It integrates detection, classification, and hot-swap control functions compliant with IEEE 802.3af Clause 33.

Its dual-level current limit architecture separates inrush (140 mA typ.) from steady-state (375 mA typ.) operation to prevent PSE misclassification during capacitor charging. Signature disable (SIGDISA) allows invalid signature presentation by grounding the pin, supporting legacy LAN systems while maintaining 802.3af interoperability.

Key Specifications

Parameter	Value and Actual Design Meaning
IEEE Compliance	Fully compliant with IEEE 802.3af Clause 33 for PD detection, classification, and power delivery
UVLO Threshold	Rising: –36.0 V (relative to GND); falling: –30.5 V - ensures stable startup and brownout recovery
Inrush Current Limit	140 mA typical - limits surge during input capacitor charging to avoid PSE fault tripping
Normal Operation Limit	375 mA typical - sustains Class 3 power (up to 12.95 W at PD input) under steady load
Signature Resistor	25 kΩ integrated - meets IEEE 802.3af 2-point measurement requirement (23.25–26.00 kΩ range)
Thermal Protection	Single-step latch mode - shuts down permanently until manual reset after overtemperature event
Power Good Output	Open-drain, active-low referenced to VIN - signals MOSFET full conduction and stable VOUT rail

Pinout & Package

STHS4257A1M6F is packaged in SO8 (M6F suffix denotes SO-8 narrow, 150 mil width), with pins arranged per top-view layout: Pin 1/3/7 = NC; Pin 2 = RCLASS (classification resistor connection); Pin 4 = VIN (negative return to PSE); Pin 5 = VOUT (negative power output); Pin 6 = PWRGD (open-drain Power Good); Pin 8 = GND (positive power rail).

Pin/Terminal	Circuit Role	Design Meaning
Pin 1, 3, 7	No Connect	Unbonded; must remain floating or grounded per layout guidelines - no electrical function
Pin 2 (RCLASS)	Classification Input	Connects external resistor to VIN to select IEEE 802.3af Class 0–4; open for Class 0
Pin 4 (VIN)	Negative Return Rail	Accepts –57 V max input; interfaces directly to PSE's negative supply side of Ethernet transformer
Pin 5 (VOUT)	Negative Power Output	Delivers regulated negative rail to downstream DC/DC converter; referenced to GND
Pin 6 (PWRGD)	Power Good Indicator	Active-low open-drain signal pulled to VIN - asserts when MOSFET is fully on and VOUT ≥ 3.0 V above VIN
Pin 8 (GND)	Positive Power Rail	Serves as system ground reference and positive supply node for internal circuitry and external loads

Key Features

Feature	Design Value
Integrated Low-Side MOSFET	100 V breakdown, 1.0 Ω R_ON max - eliminates external switch and reduces BOM count in PoE front-end
Signature Disable (SIGDISA)	Pin 7 (SO8) tied to GND disables 25 kΩ signature - enables interoperability with non-802.3af PSEs
Resistor-Programmable Classification	Supports Class 0–3 via RCLASS (45.3 Ω to open) - enables precise power budgeting per IEEE 802.3af Table 3
Two-Stage Current Limiting	140 mA inrush → 375 mA normal - prevents false PSE disconnect during C2 charging while sustaining full Class 3 load
Latched Thermal Shutdown	Shuts off MOSFET at 140 °C and holds off until power cycle - protects against sustained overload in enclosed environments

Applications

Voice over IP (VoIP) Phones

WLAN Access Points

Use Scenario: Powered via Ethernet cable in office or enterprise deployments without local AC adapter.

IC Role / Device Role / Timing Role: PD interface controller managing detection, classification, and safe power ramp-up before enabling voice codec and PHY.

Use Value: Enables single-cable deployment with guaranteed Class 3 power (up to 12.95 W) and automatic fault recovery via latched shutdown.

Use Scenario: Wall-mounted or ceiling-mounted wireless infrastructure requiring remote power and minimal footprint.

IC Role / Device Role / Timing Role: Hot-swap controller regulating inrush into large bulk capacitance while signaling readiness to host MCU via PWRGD.

Use Value: Eliminates need for discrete TVS + MOSFET + sense resistor, reducing board area and qualification effort for FCC/CE PoE compliance.

Web Cameras

POS Terminals

Use Scenario: High-resolution IP cameras deployed in retail or security systems using existing Cat5e cabling.

IC Role / Device Role / Timing Role: Provides IEEE-compliant signature and classification while isolating camera sensor and ISP from PSE transients.

Use Value: Integrated 25 kΩ signature and –57 V absolute max rating ensure robust operation across varying PSE implementations.

Use Scenario: Compact point-of-sale terminals in retail kiosks powered over Ethernet for simplified installation.

IC Role / Device Role / Timing Role: Controls power sequencing to EMV payment module and display backlight, with PWRGD enabling firmware boot only after stable rail.

Use Value: Latch-mode thermal protection prevents intermittent reboot during extended transaction processing under ambient heat.

Equivalent & Alternatives

The following parts are listed as comparable options for similar PoE PD interface applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
LT4275IMS#PBF	Higher UVLO (–42.5 V rise), auto-retry thermal response, no SIGDISA pin	Requires external signature resistor; better suited for new designs needing fault auto-recovery	Select if latching behavior is undesirable and system can tolerate restart cycles during thermal events
TPS23753APW	Integrated DC/DC controller, higher current (600 mA), no signature disable	Reduces external components but lacks SIGDISA - incompatible with legacy PSEs requiring invalid signature	Choose when integrating isolated flyback control is prioritized over backward compatibility with older PoE infrastructure

Compared with LT4275IMS#PBF and TPS23753APW, STHS4257A1M6F uniquely supports signature disable for legacy LAN interoperability, uses latch-mode thermal protection for deterministic fault containment, and delivers Class 3 power with minimal external components - making it optimal for cost-sensitive, field-deployed VoIP and surveillance endpoints.

Availability

STHS4257A1M6F is available at Aetrix Electronics and suitable for Voice over IP (VoIP) phones, WLAN access points, and web cameras requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for STHS4257A1M6F 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, delivering intelligent power, analog, MEMS, and microcontroller solutions for industrial, automotive, and consumer markets.

STHS4257A1M6F belongs to ST's PoE PD interface controller product line, engineered specifically for IEEE 802.3af-compliant endpoint devices requiring integrated signature, classification, and robust hot-swap protection in compact SO8 packages.

FAQ

What is the purpose of the SIGDISA pin on STHS4257A1M6F?

The SIGDISA pin (Pin 7 in SO8) disables the internal 25 kΩ signature resistor when pulled to GND, presenting an invalid signature to the Power Sourcing Equipment (PSE). This enables interoperability with legacy non-802.3af PSEs or systems requiring manual signature control. It is internally pulled up to VIN and unused pins should be left floating or tied to VIN.

How does the dual-level current limiting work during power-up?

At startup, STHS4257A1M6F enforces a 140 mA inrush current limit to charge the output capacitor safely. Once VOUT rises above the Power Good threshold (~3.0 V above VIN), it automatically switches to the 375 mA normal-operation limit. This prevents PSE misclassification during transient charging while sustaining full Class 3 load capability thereafter.

Why does STHS4257A1M6F use negative voltage referencing?

The device operates with VIN as the negative rail (–48 V typical) and GND as the positive rail to accommodate the diode bridge used in PoE inputs. This polarity-insensitive architecture allows the same hardware to accept power regardless of Ethernet pair polarity. All voltage specifications (e.g., UVLO, signature) are defined relative to GND, with negative magnitudes indicating actual operating polarity.

Can STHS4257A1M6F support IEEE 802.3at (PoE+) or 802.3bt?

No - STHS4257A1M6F is strictly IEEE 802.3af (PoE Type 1) compliant and rated for up to Class 3 (12.95 W at PD input). It lacks the higher current capability, multi-event classification, and auxiliary power detection required for 802.3at or 802.3bt. For PoE+ designs, ST's STPD802 or TI's TPS2373 series are appropriate alternatives.

STHS4257A1M6F Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: 8-SOIC (0.154", 3.90mm Width)

Packaging:: Tape & Reel (TR)

Product Status:: Obsolete

Type:: Controller (PD)

Number of Channels:: 1

Power - Max:: 12.95 W

Internal Switch(s):: Yes

Auxiliary Sense:: No

Standards:: 802.3af (PoE)

Voltage - Supply:: 57V (Max)

Current - Supply:: 330µA

Operating Temperature:: -40°C ~ 85°C

Mounting Type:: Surface Mount

Supplier Device Package:: 8-SOIC

STHS4257A1M6F FAQ

1.How can I place an order for STHS4257A1M6F through Aetrix?

Please submit a Request for Quotation (RFQ) for STHS4257A1M6F 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 STHS4257A1M6F reliable?

The price and inventory of STHS4257A1M6F are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for STHS4257A1M6F is usually 5 days.

3.What payment methods are accepted for STHS4257A1M6F?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for STHS4257A1M6F transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for STHS4257A1M6F?

STHS4257A1M6F orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your STHS4257A1M6F 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 STHS4257A1M6F?

For technical support, including STHS4257A1M6F datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your STHS4257A1M6F requirements.

6.How does Aetrix verify that STHS4257A1M6F is sourced from the original manufacturer or authorized distributors?

All STHS4257A1M6F 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 STHS4257A1M6F meets industry standards.

7.What is the process for return or replacement of STHS4257A1M6F?

All STHS4257A1M6F units undergo pre-shipment inspection (PSI). If there is an issue with STHS4257A1M6F, 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 STHS4257A1M6F part is unused and in its original packaging.

Return procedure for STHS4257A1M6F:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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