Allegro MicroSystems A5350CA

Overview

A5350CA from Allegro MicroSystems is a discontinued BiCMOS ionization smoke detector IC with interconnect capability, 5.0 μA typical standby current at 9 V, 1.67 s oscillator period in standby, and support for up to 125-unit daisy-chained alarm networks. It integrates piezoelectric horn drivers (HORN1/HORN2), active guard amplifiers (GUARD1/GUARD2), and low-battery detection with adjustable threshold via LOW-V SET pin - deployed in battery-powered residential/commercial smoke alarms.

For engineers reviewing the A5350CA datasheet, A5350CA pinout, A5350CA application, or A5350CA equivalent, key selection considerations include its discontinued status, 16-pin DIP package, inverted alarm polarity on DETECT IN, ultra-low-power timing architecture (10 ms sensing per 1.67 s cycle), and compatibility with ionization chambers requiring external sensitivity tuning via SENSITIVITY SET resistor divider.

Technical Context

The A5350CA implements a strobed sensing architecture: internal power is applied for only 10 ms every 1.67 s to minimize average current; smoke detection occurs during this window by comparing DETECT IN voltage against SENSITIVITY SET reference. Every 24 cycles (~40 s), it performs low-battery check using an internal bandgap reference and pulses LED output.

Interconnect functionality uses open-drain I/O pin with 3 s delay and 93.9 ms noise-immune latch window; alarm propagation requires sustained high state across three consecutive sped-up oscillator periods (41.67 ms each). Guard amplifiers on pins 14 and 16 maintain ±100 mV offset relative to DETECT IN to suppress surface leakage in ion chambers.

Key Specifications

Pinout & Package

Package: 16-pin plastic dual in-line package (DIP), 0.3" wide, RoHS-compliant (suffix -T variant available).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar ionization smoke detector controller applications.

Compared with A5350CA, A5351CA offers direct replacement capability with no PCB changes and improved ESD tolerance, while A5370CA serves a different sensing modality and demands chamber- and schematic-level redesign.

Availability

A5350CA is available at Aetrix Electronics and suitable for legacy repair, end-of-life system maintenance, and certified retrofit programs requiring stable component supply for ionization smoke alarm field replacements.

Supply support for A5350CA 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

Allegro MicroSystems is a U.S.-based designer of high-performance magnetic sensing and power ICs, headquartered in Worcester, Massachusetts, with global manufacturing and support infrastructure.

The A5350CA belongs to Allegro's dedicated smoke detector IC product line, engineered specifically for ultra-low-power, battery-operated life-safety applications requiring regulatory compliance (UL 217, EN 14604) and long-term field reliability.

FAQ

Is the A5350CA still in production?

No, the A5350CA is a discontinued product. Allegro MicroSystems classified it as "Not for New Design" effective May 4, 2009, and ceased production. It remains available through authorized distributors like Aetrix Electronics for legacy system support and certified repair programs, but samples are no longer provided and long-term supply is limited.

What is the function of the inverted alarm polarity on the A5350CA's DETECT IN pin?

The A5350CA's DETECT IN pin uses inverted polarity: an alarm is triggered when the input voltage rises *above* the SENSITIVITY SET reference voltage. This matches the natural discharge behavior of ionization chambers under smoke conditions, where reduced ion current causes chamber voltage to increase - enabling direct, polarity-matched interface without external inversion circuitry in the A5350CA design.

Can the A5350CA be used with photoelectric smoke chambers?

No, the A5350CA is optimized for ionization chambers and relies on active guard amplifiers (GUARD1/GUARD2) and specific input offset tolerances (±50 mV) calibrated for ion current levels. Photoelectric chambers produce different signal characteristics and lack the surface leakage concerns addressed by the A5350CA's guard architecture. For photoelectric use, Allegro recommends the A5370CA instead.

How does the A5350CA achieve 5 μA standby current?

The A5350CA achieves 5 μA typical standby current through a strobed architecture: the entire circuit powers down for 1.66 seconds, then activates for only 10 ms to perform smoke sampling and internal housekeeping. This duty cycle - combined with BiCMOS process optimization and minimal biasing - reduces average current draw while maintaining reliable detection performance across the –10°C to 60°C operating range.

What is the purpose of the FEEDBACK pin on the A5350CA?

The FEEDBACK pin on the A5350CA serves a dedicated test function: during factory calibration or bench verification, pulling FEEDBACK low during power-up enables accelerated low-battery testing. When VDD is gradually reduced, the A5350CA drives HORN1 high precisely at the programmed low-battery threshold - allowing precise validation of the LOW-V SET configuration without requiring full system integration or real-time smoke simulation.