Broadcom Limited ASSR-4120-302E

Overview

ASSR-4120-302E from Broadcom is a dual-channel, normally-off, solid-state relay (Photo MOSFET) with optically isolated input and two independent high-voltage MOSFET outputs. It delivers 400 V output withstand voltage, 0.12 A average output current per channel, 16 Ω typical on-resistance at 25°C, and operates across –40°C to +85°C for industrial signal switching and low-power AC/DC load control.

For engineers reviewing the ASSR-4120-302E datasheet, pinout, applications, or equivalent options, key selection considerations include dual SPST Form A relay equivalence, 3750 Vrms input-output isolation, gull-wing surface-mount DIP-8 package compatibility, and fast 0.25 ms turn-on / 0.02 ms turn-off timing under 5 mA drive.

Technical Context

The ASSR-4120-302E integrates an AlGaAs infrared LED optically coupled to a photovoltaic diode array and driver circuit that controls two discrete high-voltage MOSFETs. Its dual-channel architecture enables independent switching of two isolated loads without shared terminals.

It uses internal turn-off circuitry to ensure reliable contact opening at ≤0.8 V input voltage and requires only ≥3 mA LED forward current to close either channel. The device meets UL1577 (3750 Vrms, 1 min) and CSA Component Acceptance #5 for reinforced insulation in safety-critical systems.

Key Specifications

Pinout & Package

ASSR-4120-302E is housed in an 8-pin DIP gull-wing surface-mount package (300-mil width), with pins 1–4 forming the isolated input side (LED anode/cathode pair per channel) and pins 5–8 serving as the two independent output channels (source/drain pairs). The package supports reflow soldering per JEDEC J-STD-020 lead-free profile.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar solid-state relay applications.

Compared with TLP3548A and VO3120, the ASSR-4120-302E offers optimal integration density and speed for dual-channel low-power switching, balancing isolation strength, thermal derating behavior, and gull-wing mountability in space-constrained industrial designs.

Availability

ASSR-4120-302E is available at Aetrix Electronics and suitable for industrial PLC I/O modules, telecom signal routing, medical diagnostic equipment, and security system control panels requiring stable component supply, long-term lifecycle support, and RoHS-compliant sourcing.

Supply support for ASSR-4120-302E 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

Broadcom Inc. is a global semiconductor leader specializing in infrastructure software, networking, and optoelectronic components for data center, enterprise, and industrial applications.

The ASSR-41xx series was designed to replace electromechanical relays in general-purpose signal and low-power load switching, emphasizing reliability, miniaturization, and regulatory compliance across harsh operating environments.

FAQ

What is the maximum operating temperature range for the ASSR-4120-302E?

The ASSR-4120-302E is specified to operate reliably from –40°C to +85°C ambient temperature. This range is validated across all electrical parameters including output current derating, on-resistance stability, and isolation integrity. Thermal performance data in Figures 3 and 4 of the AV02-0279EN datasheet confirm sustained 0.12 A per channel up to 85°C with appropriate PCB copper area. The ASSR-4120-302E must not exceed 125°C junction temperature during operation.

Does the ASSR-4120-302E support AC and DC loads on the same output channel?

Yes, the ASSR-4120-302E supports both AC and DC loads on each output channel, with a 400 V peak blocking voltage and bidirectional conduction capability. Its MOSFET-based output structure allows zero-crossing–independent switching, unlike TRIAC-based SSRs. However, for DC-only operation, the ASSR-4111 variant achieves lower R_ON (5.5 Ω); the ASSR-4120-302E maintains 16 Ω typical R_ON regardless of load type.

What is the minimum input current required to turn on the ASSR-4120-302E?

The ASSR-4120-302E turns on with a minimum input current of 3 mA through either LED input pair (pins 1–2 or 3–4). While the device may activate at lower currents (≥0.5 mA), Broadcom specifies 3 mA as the guaranteed threshold across –40°C to +85°C. For robust operation over temperature and lifetime, 5–10 mA is recommended, as confirmed in the Recommended Operating Conditions table on page 9 of AV02-0279EN.

How does the ASSR-4120-302E achieve its 3750 Vrms isolation rating?

The ASSR-4120-302E achieves 3750 Vrms input-output isolation via internal optocoupling with reinforced insulation: an AlGaAs LED optically triggers a photovoltaic diode array separated by ≥0.08 mm internal plastic gap, with 7.4 mm creepage and 7.1 mm clearance across the DIP-8 body. This construction complies with UL1577 and CSA Component Acceptance Notice #5, verified by 1-minute dielectric withstand testing at 3750 Vrms under ≤50% RH conditions.

Can the ASSR-4120-302E be used in medical equipment requiring IEC 60601-1 compliance?

Yes, the ASSR-4120-302E supports IEC 60601-1 compliance in medical systems due to its 3750 Vrms isolation, IIIa insulation group, CTI ≥175 V, and 7.4 mm creepage - exceeding the 4 mm minimum required for 2× MOPP (Means of Patient Protection) in many configurations. Final system-level validation is required, but the ASSR-4120-302E provides the foundational isolation performance needed for patient-connected diagnostics and monitoring circuits.