Microchip Technology LE75183BFSCT

Overview

LE75183BFSCT from Zarlink Semiconductor is a monolithic Line Card Access Switch (LCAS) providing solid-state equivalent functionality of three 2-form-C electromechanical relays. It delivers power ringing access, line test-out (loop access), and SLIC test-in switching for tip/ring in analog telephony line cards. Key confirmed parameters include 5 V only operation, <1.1 mA typical supply current in all-OFF state, >480 V breakdown rating on ringing access switch (SW8), and integrated thermal shutdown with battery-monitoring all-OFF fail-safe behavior.

For engineers reviewing the LE75183BFSCT datasheet, LE75183BFSCT pinout, LE75183BFSCT application, or LE75183BFSCT equivalent, this page provides verified technical context, exact pin functions per 32-pin QFN package, real-world telephony switching states (e.g., simultaneous test-in/test-out), protection architecture differences between A/C and B variants, and two validated alternative parts for central office and DLC line card designs.

Technical Context

The LE75183BFSCT implements seven discrete switching states via logic-level inputs (INRING, INTESTin, INTESTout, LATCH), supporting idle/talk, power ringing, loop access, SLIC test, simultaneous loop+SLIC access, ringing generator test, and all-OFF. Its internal architecture includes break-before-make or make-before-break control logic, diode bridge + current limiting + thermal shutdown (no SCR clamping), and dedicated TSD pin for thermal flagging or disable control.

It operates exclusively from 5 V (VDD = 4.5–5.5 V), draws ≤2.1 mA during power ringing, and uses VBAT (–72 to –19 V) solely as a reference for protection circuitry - loss of battery forces immediate all-OFF state. All switches feature <1 µA off-state leakage at ±330 V and dV/dt immunity up to 200 V/µs.

Key Specifications

Pinout & Package

LE75183BFSCT is packaged in a 32-pin QFN with exposed pad (EPAD), RoHS-compliant, lead-free matte-tin plating. The EPAD has no internal electrical connection and must be soldered to an equal-sized copper pad for mechanical stability only - no VBAT or ground connection recommended.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar line card access switch applications.

Compared with LE75183AFQC, LE75183BFSCT omits SCR clamping - reducing complexity and cost where full bidirectional fault steering isn't required. Against LE75183BFSC, it delivers identical functionality in a smaller, thermally superior QFN package ideal for high-density line card designs.

Availability

LE75183BFSCT is available at Aetrix Electronics and suitable for central office, digital loop carrier, and PBX analog line card applications requiring stable component supply, long lifecycle support, and RoHS-compliant packaging.

Supply support for LE75183BFSCT 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

Zarlink Semiconductor was a fabless IC designer specializing in communications infrastructure semiconductors, later acquired by Microsemi (now Microchip). Known for high-reliability telecom solutions.

The LE75183BFSCT belongs to the VoiceEdge™ VE750 series, engineered specifically for solid-state replacement of electromechanical relays in analog telephony line cards - emphasizing low power, fail-safe behavior, and integrated protection.

FAQ

What is the primary function of the LE75183BFSCT in a telephony line card?

The LE75183BFSCT serves as a monolithic Line Card Access Switch that replaces three 2-form-C electromechanical relays. It manages tip/ring connectivity for power ringing access, line test-out (loop access), and SLIC test-in functions across seven defined telephony states - all within a single 32-pin QFN package. Its design directly targets central office and DLC line card applications requiring high reliability and low power.

Does the LE75183BFSCT require external driver circuitry for its logic inputs?

No, the LE75183BFSCT does not require external driver circuitry. Its logic inputs - INRING (75 kΩ pull-up), INTESTin (75 kΩ pull-down), INTESTout (75 kΩ pull-up), and LATCH (75 kΩ pull-down) - have internal bias resistors. This allows direct connection to TTL-level controllers, reducing component count and simplifying interface design in the LE75183BFSCT-based line card.

How does the LE75183BFSCT respond to loss of battery voltage?

The LE75183BFSCT enters an all-OFF state immediately upon loss of valid battery voltage. Since VBAT is used solely as a reference for internal protection circuitry, the device monitors it continuously: if VBAT rises above typically –10 V (indicating battery disconnect or severe degradation), LE75183BFSCT forces all switches open and remains in all-OFF until VBAT drops below –15 V. This fail-safe behavior is critical for safety compliance in central office deployments.

What protection features are integrated into the LE75183BFSCT?

The LE75183BFSCT integrates diode bridge clamping, current limiting, and thermal shutdown - but excludes SCR clamping (present in A/C versions). Positive faults are steered to ground; negative faults route to battery. Both polarities are mitigated by current limiting and thermal shutdown. A secondary protector is still required to clamp tip/ring voltage below switch breakdown limits, and foldback/crowbar types are recommended for optimal stress reduction on the LE75183BFSCT.

Which package type does the LE75183BFSCT use, and why is the exposed pad important?

The LE75183BFSCT uses a 32-pin QFN package with an exposed pad (EPAD). The EPAD has no internal electrical connection and must be soldered to an equally sized copper pad on the PCB solely for mechanical stability and improved thermal dissipation - not for grounding or powering. This construction enhances reliability in thermally demanding line card environments and supports the LE75183BFSCT's low-power, high-isolation operational profile.