Microchip Technology LE79R70DJCT

Overview

LE79R70DJCT from Zarlink Semiconductor is a bipolar monolithic Ringing Subscriber Line Interface Circuit (RSLIC) designed for short-loop telephony CPE applications. It integrates on-chip trapezoidal-wave ringing, dual battery switching (VBAT1: –40 V to –67 V; VBAT2: –19 V to VBAT1), programmable constant-current feed (IL = 18–39 mA), and two on-chip relay drivers. It serves as the core line interface in ISDN Terminal Adaptors and set-top boxes.

For engineers reviewing the LE79R70DJCT datasheet, LE79R70DJCT pinout, LE79R70DJCT application, or LE79R70DJCT equivalent, this page delivers verified electrical characteristics, validated QFN-32 pin mapping, confirmed RoHS-compliant green package details, and real-world SLIC selection guidance for voice-over-T1/E1, DSL modems, and smart residential gateways.

Technical Context

The LE79R70DJCT implements full BORSHT functionality-battery feed, overvoltage protection, ringing, supervision, hybrid, and test-with integrated ring-trip detection, ground-key sensing, and polarity reversal support. Its dual-battery architecture enables dynamic switching between VBAT1 (high-voltage standby) and VBAT2 (low-voltage active) to meet open-circuit voltage requirements for fax/MTU while minimizing power dissipation.

It features a 1000× current gain amplifier at RSN, programmable loop-detect threshold via RD resistor, and CMOS-compatible RINGIN input with external RC shaping for trapezoidal ringing. The device uses an internal VEE regulator eliminating need for external –5 V supply, and supports tip-open state for ground-start lines.

Key Specifications

Pinout & Package

LE79R70DJCT is supplied in a 32-pin thermally enhanced QFN package (8 mm × 8 mm) with exposed pad electrically tied to VBAT1. The package is RoHS-compliant, lead-free, halogen-free, and antimony-free.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LE79R70DJCT, LE79R79DJC offers identical functionality with tighter specifications for certification-critical deployments, while LE79R100DJC delivers measurable audio quality improvements at higher cost-making LE79R70DJCT the optimal balance of cost, compliance, and performance for mainstream CPE.

Availability

LE79R70DJCT is available at Aetrix Electronics and suitable for Integrated Access Devices (IADs), DSL modems, and smart residential gateways requiring stable component supply and long-term lifecycle support.

Supply support for LE79R70DJCT 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 provider specializing in communications ICs, acquired by Microsemi in 2011 and later integrated into Microchip Technology. It pioneered high-reliability SLIC solutions for global telephony infrastructure.

The LE79R70DJCT belongs to the VE580 Series RSLIC product line, engineered specifically for cost-sensitive, short-loop CPE applications including ISDN-TA, cable/DSL modems, and residential VoIP gateways-prioritizing integration, power efficiency, and regulatory compliance.

FAQ

What is the primary function of the LE79R70DJCT in a telephony system?

The LE79R70DJCT serves as a Ringing Subscriber Line Interface Circuit (RSLIC), providing full BORSHT functionality-including battery feed, ringing generation, loop supervision, hybrid conversion, and test access-for analog telephone line interfaces in CPE equipment. Its on-chip trapezoidal ringing and dual-battery switching make it especially suited for ISDN Terminal Adaptors and DSL modems where board space and power efficiency are critical. The LE79R70DJCT integrates functions previously requiring multiple discrete components, reducing system cost and complexity.

Does the LE79R70DJCT require an external negative power supply?

No, the LE79R70DJCT includes an internal VEE regulator that generates the required –5 V rail from the VNEG pin, eliminating the need for an external negative supply. This simplifies power design and reduces component count in applications such as set-top boxes and residential gateways. The VNEG pin operates from –4.75 V to VBAT2, and the internal regulator ensures stable biasing for analog circuitry without external regulation. This feature is fully implemented in the LE79R70DJCT and documented in its electrical characteristics table.

How does the LE79R70DJCT achieve power savings in standby mode?

The LE79R70DJCT achieves standby power savings through on-chip dual-battery switching: it automatically selects VBAT2 (–19 V to VBAT1) for off-hook operation and switches to VBAT1 (–40 V to –67 V) only during on-hook states requiring higher open-circuit voltage-such as for fax machine compatibility. This architecture reduces quiescent power by >50% compared to single-supply SLICs. Measured data shows standby power drops to 55–80 mW on VBAT2, versus 200–300 mW on VBAT1 in OHT state. This behavior is inherent to the LE79R70DJCT's power-feed controller and requires no external control logic.

Can the LE79R70DJCT drive external relays directly?

Yes, the LE79R70DJCT integrates two open-collector relay drivers (RYOUT1 and RYOUT2) capable of sinking up to 75 mA each with on-voltages of +0.25 V to +0.4 V at 30 mA. These outputs share a common emitter (RYE) and include internal snubber circuits, enabling direct drive of standard 5 V or 12 V electromechanical relays without external transistors or flyback diodes. The LE79R70DJCT datasheet confirms this capability in both absolute maximum ratings and relay driver schematic sections, making it ideal for FXS card and intelligent PBX applications requiring line seizure control.

What package type is used for the LE79R70DJCT, and how is thermal management handled?

The LE79R70DJCT uses a 32-pin thermally enhanced QFN package (8 mm × 8 mm) with an exposed pad that must be electrically connected to VBAT1. This construction achieves a junction-to-ambient thermal resistance (θJA) of 25°C/W-significantly better than the 45°C/W of the PLCC variant-enabling 3.00 W maximum power dissipation at 70°C ambient. Proper PCB layout-soldering the exposed pad to a large copper plane with multiple thermal vias-is required to maintain reliability under continuous ringing load. This package configuration is specified for the LE79R70DJCT in Zarlink's ordering information and physical dimensions documentation.