Microchip Technology LE79R79-2DJCT

Overview

LE79R79-2DJCT from Zarlink Semiconductor is a bipolar monolithic Ringing Subscriber Line Interface Circuit (RSLIC) designed for short-loop telephony applications. It integrates on-chip trapezoidal ringing, programmable constant-current feed (IL = 20–39 mA), on-hook transmission, and dual battery switching (VBAT1: –40.5 to –75 V; VBAT2: –19 V to VBAT1). It delivers 63 dB longitudinal balance in reverse polarity mode and supports ISDN-TA, DSL modems, and intelligent PBX systems.

For engineers reviewing the LE79R79-2DJCT datasheet, LE79R79-2DJCT pinout, LE79R79-2DJCT application, or LE79R79-2DJCT equivalent, this device is selected for cost-sensitive CPE voice interface designs requiring integrated ringing, low standby power, programmable loop-detect threshold, ground-key detection, and compliance with LSSGR five-ringer equivalent voltage (66–69 Vpk).

Technical Context

The LE79R79-2DJCT implements BORSHT functions-battery feed, overvoltage protection, ringing, supervision, hybrid, and test-with on-chip ring-trip detection, polarity reversal (enabled in -2 variant), and two open-collector relay drivers (RYOUT1/RYOUT2). Its DC-feed control uses RDC/RSN node with current gain = 1000, enabling precise loop-current programming via external resistor networks.

It operates across commercial (0–70°C) and industrial (–40–85°C) temperature ranges, supports CMOS-compatible RINGIN input, and features internal VEE regulation eliminating need for external –5 V supply. Battery switching logic (B2EN pin) automatically selects VBAT2 during off-hook active state for power savings and VBAT1 during on-hook standby to meet fax/MTU open-circuit voltage requirements.

Key Specifications

Pinout & Package

LE79R79-2DJCT is housed in a 32-pin PLCC (Plastic Leaded Chip Carrier) green RoHS-compliant package with exposed thermal pad not applicable (QFN variant has exposed pad; PLCC does not). Pin 1 is marked for orientation; NC pins are internally unconnected.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LE79R79-2DJC, the -1DJC offers lower longitudinal rejection but simpler control, while the LE79R100-2DJC shifts from analog SLIC-only to mixed-signal SoC functionality-requiring PCB redesign and firmware adaptation.

Availability

LE79R79-2DJCT is available at Aetrix Electronics and suitable for ISDN terminal adaptors, DSL modems, smart residential gateways, and intelligent PBX systems requiring stable component supply, long-lifecycle support, and RoHS-compliant green packaging.

Supply support for LE79R79-2DJCT 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 of high-performance analog and mixed-signal ICs for communications infrastructure, specializing in telephony interface solutions before its acquisition by Microsemi in 2011.

The LE79R79 belongs to Zarlink's VE580 Series RSLIC product line, engineered specifically for cost-optimized, short-loop CPE voice interfaces where integrated ringing, low standby power, and programmable supervision reduce system-level BOM and design complexity.

FAQ

What is the primary function of the LE79R79-2DJCT in a telephony system?

The LE79R79-2DJCT serves as a Ringing Subscriber Line Interface Circuit (RSLIC), providing full BORSHT functionality-including battery feed, ringing generation, supervision, hybrid conversion, and test support-for analog telephone line interfaces. In systems like DSL modems or ISDN-TAs, the LE79R79-2DJCT manages DC loop current, delivers trapezoidal ringing voltage up to 69 Vpk, detects hook status and ground key events, and enables polarity reversal-all within a single 32-pin PLCC package.

How does the LE79R79-2DJCT achieve 63 dB longitudinal balance, and why is that important?

The LE79R79-2DJCT achieves 63 dB longitudinal balance in reverse polarity mode through precision-matched internal amplifier stages and optimized layout, as verified in the datasheet's Longitudinal Performance table. This high rejection ratio suppresses common-mode noise coupling from the line into the receive path-critical in multi-line DSL modems or PBX cards where crosstalk could degrade voice quality or cause false ring detection. The -2 suffix explicitly denotes this performance grade.

Can the LE79R79-2DJCT operate without an external –5 V supply?

Yes. The LE79R79-2DJCT includes an internal VEE regulator that generates the required negative bias from VNEG, eliminating the need for an external –5 V power supply. VNEG is specified from –4.75 V to VBAT2, and the internal regulation ensures stable operation across temperature and load-reducing system power supply complexity and component count in compact CPE designs using the LE79R79-2DJCT.

What is the role of the RDC and RSN pins on the LE79R79-2DJCT?

RDC and RSN form the core of the LE79R79-2DJCT's programmable constant-current feed architecture. RSN is the receive summing node where metallic current equals 1000× the injected current; RDC connects the external feed-resistor network to RSN. Together, they allow precise setting of loop current (e.g., 20–39 mA) using standard resistors-enabling robust line feed across varying loop lengths without trimming or calibration in production for the LE79R79-2DJCT.

Does the LE79R79-2DJCT support polarity reversal, and how is it enabled?

Yes-the LE79R79-2DJCT supports polarity reversal, as indicated by the "-2" in its part number per Zarlink's Ordering Information. Polarity reversal is activated via the C3–C1 control pins (decoded per Table on page 13) and requires proper sequencing of RYOUT1/RYOUT2 relay drivers. Unlike the -1 variant, the -2 grade guarantees reverse-polarity longitudinal balance at 63 dB, making it suitable for applications like intelligent PBX FXS cards where polarity-swapped signaling is mandated.