Skyworks Solutions Inc. SI3500-A-GM

Overview

SI3500-A-GM from Silicon Laboratories is a highly-integrated 42–57 V input DC-DC converter IC with integrated PWM controller, 0.3–0.86 Ω switching N-FET, dual-level hot-swap switch (140 mA inrush / 400 mA operating), and configurable non-isolated or isolated topology support. It delivers up to 10 W output power with adjustable 1.8–12 V output voltage and operates at 350 kHz fixed frequency - used in Power over Ethernet power sourcing supplies such as Si3452.

For engineers reviewing the SI3500-A-GM datasheet, SI3500-A-GM pinout, SI3500-A-GM application, or SI3500-A-GM equivalent, key selection considerations include its 5x5 mm QFN-20 package, integrated 65 V input clamp, dual-current-limit hot-swap protection, soft-start control via external capacitor, and support for both buck-derived non-isolated and flyback-based isolated topologies.

Technical Context

The SI3500-A-GM integrates a constant-frequency 350 kHz PWM controller with internal precision 1.23 V feedback reference and error amplifier output (EROUT) for optocoupler-driven isolated feedback loops. Its switching FET features 0.3–0.86 Ω on-resistance and supports duty cycle limiting to 50% when ISOSSFT is tied to VDD.

It implements a two-stage hot-swap function: initial 140 mA inrush current limit during input capacitor charging, then automatic transition to 400 mA operating current limit once VHSO drops below threshold; thermal shutdown activates at 160 °C with 25 °C hysteresis.

Key Specifications

Pinout & Package

SI3500-A-GM uses a low-profile, RoHS-compliant 5×5 mm, 20-pin QFN package with exposed thermal pad (VNEG) requiring ≥9 thermal vias to a 2 in² ground plane.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-voltage DC-DC converter applications.

Compared with LM5165QPWPRQ1 and MAX5033BASA+, the SI3500-A-GM uniquely combines 42–57 V operation, integrated hot-swap with dual current limits, 65 V input clamp, and native support for both isolated and non-isolated topologies - reducing total component count and improving system-level surge resilience.

Availability

SI3500-A-GM is available at Aetrix Electronics and suitable for Power over Ethernet infrastructure, industrial 48 V power conversion, and isolated auxiliary supply designs requiring stable component supply across extended temperature ranges (–40 to +85 °C).

Supply support for SI3500-A-GM 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

Silicon Laboratories is a U.S.-based semiconductor company specializing in mixed-signal ICs for timing, connectivity, and power management, with deep expertise in energy-efficient analog-intensive solutions.

The SI3500-A-GM belongs to Silicon Labs' high-voltage DC-DC converter product line, designed specifically for PoE power sourcing equipment and industrial 48 V systems requiring integrated protection, compact footprint, and topology flexibility.

FAQ

What is the recommended input voltage range for the SI3500-A-GM?

The SI3500-A-GM is specified for continuous operation across 42 V to 57 V DC input. Its internal 65 V Zener clamp protects against transients up to 80 V (5 A, 50 µs), making it suitable for PoE+ and industrial 48 V systems with line variation and hot-plug events. Operation outside this range may trigger undervoltage lockout (<42 V) or exceed absolute maximum ratings (>57 V).

Can the SI3500-A-GM be used in isolated flyback topologies?

Yes, the SI3500-A-GM supports isolated configurations using its EROUT pin to drive an optocoupler and ISOSSFT pin to control soft-start ramping of the PWM duty cycle clamp. When ISOSSFT is connected to VSSA via a 0.1 µF capacitor, the device enters isolated mode and limits maximum duty cycle to 50%, preventing transformer saturation - a key requirement for safe flyback operation.

How does the dual-level hot-swap function work in the SI3500-A-GM?

The SI3500-A-GM implements two distinct hot-swap current limits: a 140 mA inrush limit during initial input capacitor charging, followed by automatic transition to a 400 mA operating limit once the HSO voltage drops below threshold. This prevents input surge damage while enabling full-load operation after startup - all without external current-sense resistors or control logic.

What thermal management is required for full 10 W operation of the SI3500-A-GM?

To sustain 10 W output at full load, the SI3500-A-GM requires its VNEG thermal pad to be connected via ≥9 thermal vias to a minimum 2 in² copper heat spreader plane. With this layout, the device achieves θJA = 44 °C/W, allowing operation up to +85 °C ambient. Without adequate thermal relief, junction temperature may exceed 160 °C, triggering thermal shutdown.

Is the SI3500-A-GM still recommended for new designs?

No - the SI3500-A-GM is marked "Not Recommended for New Designs" per Silicon Labs Rev. 1.2 documentation. While fully functional and supported for existing production, new designs should evaluate Silicon Labs' newer alternatives (e.g., Si3404/Si3406 series) or consult Aetrix Electronics for qualified drop-in replacements with enhanced efficiency, integration, or lifetime assurance.