Microchip Technology LE79555-2BVC

Overview

LE79555-2BVC from Zarlink Semiconductor is a Subscriber Line Interface Circuit (SLIC) designed for high-density POTS linecards, supporting Active, Reverse Polarity, Tip Open, Ringing, Standby, and Open Circuit control states with –40 to –58 V battery operation, programmable constant-current feed up to 30 mA, and on-chip switching regulator for low power dissipation.

For engineers reviewing the LE79555-2BVC datasheet, LE79555-2BVC pinout, LE79555-2BVC application, or LE79555-2BVC equivalent, this device delivers verified performance in short/long loop telephony systems requiring low standby power, ground-start detection, and integrated relay drivers - all in a 44-pin TQFP package compliant with RoHS Directive 2002/95/EC.

Technical Context

The LE79555-2BVC implements a fully integrated two-wire interface with DC feed regulation, longitudinal signal suppression, and programmable loop-detect thresholds. Its on-chip switching regulator operates at 200–600 kHz (CHCLK input), achieves >80% efficiency, and eliminates need for external –5 V supply while maintaining ≤190 mW active-state power dissipation.

Control logic accepts TTL-compatible inputs (C3–C1, D1/D2) to select six discrete operating states; supervision feedback is provided via open-collector DET output with built-in 15 kΩ pull-up. Ground-start detection is performed automatically in Active, Standby, and Tip Open states using IGK threshold (5–13 nA) and longitudinal current sensing.

Key Specifications

Pinout & Package

LE79555-2BVC is housed in a 44-pin Thin Quad Flat Package (TQFP) with exposed pad not present - distinct from the 32-pin QFN variant. Pin 1 is marked for orientation; N/C pins are unconnected internally. AGND/DGND and BGND serve separate ground domains; VBAT is the most negative battery rail; RINGOUT, RYOUT1, and RYOUT2 are open-collector outputs referenced to BGND.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar SLIC applications.

Compared with LE79555-2FQC, the LE79555-2BVC trades thermal efficiency for easier assembly and legacy board compatibility; versus LE79205-2BVC, it delivers 30% lower active power and eliminates an entire voltage rail - reducing BOM count and improving system reliability.

Availability

LE79555-2BVC is available at Aetrix Electronics and suitable for VoIP gateways, central office switches, remote terminal units, and emergency call systems requiring stable component supply and long-term lifecycle support.

Supply support for LE79555-2BVC 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 Canadian fabless semiconductor company specializing in voice, timing, and optical networking ICs before its acquisition by Microsemi in 2011. It pioneered VoiceEdge™ SLIC technology for telecom infrastructure.

The LE79555-2BVC belongs to the VE580 series, engineered specifically for high-density, low-power POTS linecards where space, thermal budget, and regulatory compliance (Bellcore GR-357-CORE) are critical design constraints.

FAQ

What is the maximum continuous battery voltage the LE79555-2BVC can withstand?

The LE79555-2BVC supports continuous VBAT operation from –40 V to –58 V. Absolute maximum rating allows –70 V for continuous use and –75 V for 10 ms transients. Exceeding these limits risks permanent damage to the internal power feed circuitry and switching regulator. Always verify local central office battery specifications before deployment.

Does the LE79555-2BVC require an external –5 V supply?

No, the LE79555-2BVC does not require an external –5 V supply. Its integrated switching regulator generates regulated internal voltages from the main VBAT rail, eliminating the need for a second negative supply. This reduces BOM cost, board area, and power conversion losses - a key differentiator from legacy SLICs like the LE79205-2BVC.

How is ground-start detection implemented in the LE79555-2BVC?

Ground-start detection in the LE79555-2BVC is performed automatically by the Ground Detector block. When longitudinal current exceeds the IGK threshold (5–13 nA) in Active, Standby, or Tip Open states, the DET pin asserts low. No external components or configuration are needed - the function is inherent to the silicon and validated across –40°C to +85°C.

What are the key differences between LE79555-2BVC and LE79555-2FQC?

The LE79555-2BVC uses a 44-pin TQFP package with higher thermal resistance (θJA = 52°C/W), while the LE79555-2FQC uses a 32-pin QFN with exposed pad and lower θJA (25°C/W). Both share identical electrical specs, control interface, and feature set. The TQFP version simplifies rework and suits legacy layouts; the QFN offers superior thermal performance in compact, high-power designs.

Can the LE79555-2BVC drive mechanical relays directly?

Yes, the LE79555-2BVC integrates three relay drivers: RINGOUT (dedicated to ringing), RYOUT1, and RYOUT2. Each is an open-collector output rated for 50 mA sink current and includes internal snubbers. They can directly drive standard 5 V or 12 V mechanical relays without external flyback diodes or transistor buffers - confirmed in the Block Diagram and Pin Descriptions sections of the datasheet.