onsemi H22A2

Overview

H22A2 from Fairchild Semiconductor is a slotted optical switch with phototransistor output, designed for object detection and position sensing in industrial encoders and limit switches. It features a 0.125-inch wide slot, 70% minimum current transfer ratio (CTR), 30 V collector-emitter breakdown voltage, and operates across -40°C to +85°C ambient temperature.

For engineers reviewing the H22A2 datasheet, pinout, applications, or equivalent options, key selection criteria include slot width tolerance, CTR consistency at 5 mA LED forward current, dark current specification, isolation voltage rating, and compatibility with 5 V logic-level interfacing circuits.

Technical Context

The H22A2 integrates an infrared GaAs LED emitter and a silicon NPN phototransistor in a single molded package with a rigid 3.18 mm (0.125") air gap slot. Its operation relies on interruption of the optical path to modulate phototransistor conduction.

It delivers DC-coupled switching response with typical rise/fall times of 15 µs/20 µs at I_F = 10 mA and R_L = 1 kΩ, and provides 5000 V_RMS input-output isolation per UL 1577 and CSA Component Acceptance Notice #5.

Key Specifications

Pinout & Package

Package: 4-pin DIP (Dual In-line Package) with through-hole mounting and integral slot structure. Body dimensions: 9.65 mm × 6.35 mm × 10.16 mm (L×W×H).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar slotted optical switch applications.

Compared with ELCS-111 and TCST2103, the H22A2 offers superior CTR margin and certified 5000 V_RMS isolation, making it preferred for safety-critical industrial motion control where long-term parametric stability and regulatory compliance are mandatory.

Availability

H22A2 is available at Aetrix Electronics and suitable for industrial limit switches, rotary encoders, printer paper path monitoring, and automated door safety systems requiring stable component supply and long-life performance.

Supply support for H22A2 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

Fairchild Semiconductor was a U.S.-based analog and power IC manufacturer acquired by ON Semiconductor in 2016; its legacy optocoupler and optoswitch portfolio remains widely deployed in industrial systems.

The H22A2 belongs to Fairchild's slotted optical switch product line, engineered specifically for non-contact position verification in harsh electromechanical environments where reliability and isolation integrity are critical.

FAQ

What is the maximum recommended LED forward current for continuous operation of the H22A2?

The H22A2 datasheet specifies 60 mA as the absolute maximum DC forward current for the internal IR LED. For reliable long-term operation, Fairchild recommends limiting I_F to 50 mA maximum with appropriate derating above 50°C ambient. Operating the H22A2 at 50 mA ensures stable CTR performance and extends device lifetime beyond 10 years in typical industrial applications.

Does the H22A2 require external pull-up resistors on its phototransistor output?

Yes, the H22A2 phototransistor output is open-collector and requires an external pull-up resistor to establish a defined logic-high state when the slot is obstructed. A 4.7 kΩ resistor to +5 V is commonly used, yielding ~1 mA output sink current when unobstructed - sufficient to drive standard TTL or CMOS inputs while maintaining noise margin. The H22A2 output stage does not include internal pull-up circuitry.

Can the H22A2 be used in safety-rated systems such as Category 3 or SIL2 applications?

The H22A2 provides 5000 V_RMS isolation certified to UL 1577 and CSA Component Acceptance Notice #5, but it is not individually certified to IEC 61508 or ISO 13849. For Category 3 or SIL2 implementation, system-level validation is required. The H22A2 may serve as a subsystem sensor in such designs, but final safety certification depends on full architecture analysis - the H22A2 alone does not fulfill functional safety certification requirements.

What is the typical dark current of the H22A2 phototransistor at 25°C and 85°C?

The H22A2 exhibits a maximum dark current (I_CEO) of 100 nA at 25°C and 500 nA at 85°C, measured at V_CE = 10 V with the slot fully obstructed. This low leakage ensures minimal false-trigger risk in high-impedance interfacing circuits. These values are confirmed in the original Fairchild H22A2 datasheet and remain valid for all units manufactured under the Fairchild brand prior to the ON Semiconductor acquisition.

Is the H22A2 compatible with surface-mount assembly processes?

No, the H22A2 uses a through-hole 4-pin DIP package and is not designed for reflow soldering or pick-and-place SMT assembly. Its body height (10.16 mm) and lead spacing (2.54 mm) are optimized for wave soldering or hand-soldering in industrial control PCBs. Attempting SMT placement would risk mechanical damage to the slot structure and misalignment of the optical path. For SMT-compatible alternatives, consider the H22A2-SM variant or equivalent surface-mount slotted switches.