NXP Semiconductors KIT34670EGEVBE

Overview

KIT34670EGEVBE from Freescale Semiconductor is an IEEE 802.3af Power over Ethernet (PoE) Powered Device (PD) evaluation kit built around the MC34670EG IC. It integrates a full PoE interface-including signature detection, classification, inrush current limiting, and adjustable undervoltage lockout-with a high-efficiency current-mode switching regulator driving an external MOSFET. Designed for 5 V/2 A isolated DC/DC conversion in VoIP phones, IP cameras, and wireless access points.

For engineers reviewing the KIT34670EGEVBE datasheet, KIT34670EGEVBE pinout, KIT34670EGEVBE application, or KIT34670EGEVBE equivalent, this kit enables rapid validation of IEEE 802.3af PD compliance, thermal behavior under 37–57 V input, soft-start sequencing, and isolated feedback design using optocoupler + TLV431.

Technical Context

The KIT34670EGEVBE implements a complete PoE PD front-end with integrated isolation switch and classification resistor network, supporting all four IEEE 802.3af classes (0–3) via RCLA-to-VIN configuration. Its current-mode PWM controller operates at 175–325 kHz (default), adjustable to 80–480 kHz via FREQ pin resistor, with 50% duty cycle limit and internal slope compensation scaled to switching frequency.

It delivers regulated 5 V output at up to 2 A using an external N-channel MOSFET and sense resistor, with feedback via FB/COMP pins. Isolation is achieved through optocoupler-based secondary-side regulation (TLV431 + PC817), while primary-side bias is supplied by the internal 9 V VDD regulator or optional auxiliary winding.

Key Specifications

Availability

KIT34670EGEVBE is available at Aetrix Electronics and suitable for PoE-powered VoIP endpoints, IP surveillance cameras, IEEE 802.3af-compliant wireless APs, and industrial IoT edge nodes requiring stable component supply and pre-validated reference design support.

Supply support for KIT34670EGEVBE 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

Freescale Semiconductor (now part of NXP Semiconductors) is a fabless semiconductor company specializing in analog, mixed-signal, and power management ICs for automotive, industrial, and communications applications.

The MC34670 product line was designed specifically to simplify IEEE 802.3af PD implementation by integrating PoE interface logic, protection circuitry, and a high-current gate driver into a single SOICW-20 package - targeting cost-sensitive, space-constrained networked devices.

FAQ

What is the primary function of the KIT34670EGEVBE evaluation kit?

The KIT34670EGEVBE evaluation kit demonstrates and validates the MC34670EG IC as a complete IEEE 802.3af Powered Device solution. It implements signature detection, classification (Classes 0–3), inrush current limiting, undervoltage lockout, and a 5 V/2 A isolated DC/DC converter using external MOSFET and transformer. The KIT34670EGEVBE allows engineers to verify timing sequences, thermal performance, and compliance margins before final PCB layout.

Does the KIT34670EGEVBE support isolated or non-isolated DC/DC topologies?

The KIT34670EGEVBE supports isolated flyback topology using optocoupler feedback (PC817 + TLV431) referenced to secondary ground, as shown in Figure 16 and validated in efficiency plots. It does not implement non-isolated buck or buck-boost configurations; the reference design requires transformer isolation to meet PoE safety standards and achieve the specified 5 V output with galvanic separation from the Ethernet port.

What are the key thermal characteristics of the KIT34670EGEVBE during full-load operation?

Under 48 V input and 2 A load, the KIT34670EGEVBE's MC34670EG IC reaches junction temperatures near 120 °C on standard 4-layer JEDEC test board (RθJA = 103 °C/W). Thermal shutdown activates at 165 °C typical, with 30 °C hysteresis. The KIT34670EGEVBE includes copper pour and thermal vias under the SOICW-20 footprint to sustain continuous operation within -40 °C to +85 °C ambient.

Can the KIT34670EGEVBE be used to evaluate Class 4 PD operation?

No - the KIT34670EGEVBE is configured for Classes 0–3 only. Although the MC34670EG datasheet lists Class 4 classification current (36–44 mA), the KIT34670EGEVBE board uses a fixed 169 Ω RCLASS resistor (Class 3) and lacks jumper options or documentation for Class 4. IEEE 802.3af reserves Class 4 for future use and does not define power delivery limits; the KIT34670EGEVBE hardware and test procedures do not validate Class 4 functionality.

How is soft-start implemented and controlled on the KIT34670EGEVBE?

The KIT34670EGEVBE implements soft-start via the SS pin: an internal 5 µA current source charges an external capacitor (CSS), generating a voltage ramp from 0 V to 2.6 V. When SS reaches 0.6 V, GATE driver enables; full regulation begins at 2.6 V. The KIT34670EGEVBE uses a 100 nF capacitor yielding ~20 ms soft-start time. This prevents output overshoot and limits inrush into output capacitors during cold start.