Microchip Technology LE79R79-1FQC

Overview

LE79R79-1FQC from Zarlink Semiconductor is a bipolar monolithic Ringing Subscriber Line Interface Circuit (R-SLIC) designed for short-loop telephony CPE applications. It integrates on-chip trapezoidal ringing, programmable constant-current feed (IL = 20–39 mA), on-hook transmission (OHT), and dual battery switching (VBAT1: –40.5 to –75 V; VBAT2: –19 V to VBAT1). It delivers 66–69 Vpk ringing output into 1570 Ω and supports ISDN-TA, DSL modems, and smart residential gateways.

For engineers reviewing the LE79R79-1FQC datasheet, LE79R79-1FQC pinout, LE79R79-1FQC application, or LE79R79-1FQC equivalent, key selection criteria include longitudinal balance (52 dB, normal polarity), integrated ring-trip detection, ground-key/loop-detect threshold programmability, and QFN-32 green RoHS-compliant packaging with exposed thermal pad tied to VBAT1.

Technical Context

The LE79R79-1FQC implements full BORSHT functionality-battery feed, overvoltage protection, ringing, supervision, hybrid, and test-with on-chip trapezoidal ringing generation via CMOS-compatible RINGIN input and external RC shaping network. Its dual-battery architecture switches between VBAT1 (high-voltage standby) and VBAT2 (low-voltage active) to meet LSSGR five-ringer voltage requirements while minimizing power dissipation in off-hook states.

It features a 1000× current gain at RSN node for precise loop-current sensing, programmable open-circuit voltage via RSGH/RSGL resistors, and two open-collector relay drivers (RYOUT1/RYOUT2) with built-in 15 kΩ pull-up on DET output. Supervision includes polarity reversal option (enabled by -1 suffix), ground-key detection, and tip-open capability for ground-start signaling.

Key Specifications

Pinout & Package

LE79R79-1FQC uses a 32-pin QFN package with exposed thermal pad electrically connected to VBAT1. The package is green (RoHS-compliant), halogen-free, and lead-free, with matte-tin plating compatible with lead-free reflow profiles (peak ≤ 245°C).

Key Features

Applications

Equivalent & Alternatives

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

Compared with LE79R79-2FQC, LE79R79-1FQC offers lower-cost compliance for North American LSSGR applications; compared with LE79R100-1FQC, it provides optimized power efficiency and smaller footprint for short-loop CPE where 69 Vpk suffices.

Availability

LE79R79-1FQC is available at Aetrix Electronics and suitable for ISDN-TA, DSL modems, smart residential gateways, and cable modems requiring stable component supply, RoHS-compliant green packaging, and industrial temperature support (−40 to +85°C).

Supply support for LE79R79-1FQC 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 semiconductors, later acquired by Microsemi (now Microchip Technology). It pioneered high-integration SLIC solutions for telecom infrastructure and CPE.

The VE580 Series-including LE79R79-1FQC-was engineered for cost-sensitive, space-constrained short-loop telephony endpoints, emphasizing on-chip ringing, dual-battery efficiency, and programmable supervision to replace discrete SLIC+ringing transformer designs.

FAQ

What is the primary function of the LE79R79-1FQC in a telephony system?

The LE79R79-1FQC serves as a Ringing Subscriber Line Interface Circuit (R-SLIC), providing full BORSHT functionality-including battery feed, ringing generation, supervision, and hybrid functions-for analog telephone line interfaces. In systems like DSL modems or ISDN terminal adaptors, the LE79R79-1FQC replaces discrete SLIC and external ringing transformers by integrating trapezoidal ringing, dual-battery switching, and programmable loop-current feed on a single monolithic bipolar IC.

How does the LE79R79-1FQC achieve power savings in standby mode?

The LE79R79-1FQC achieves standby power savings through its dual-battery architecture: it automatically switches from high-voltage VBAT1 (−40.5 to −75 V) in on-hook/open-circuit states to low-voltage VBAT2 (−19 V to VBAT1) in off-hook/active states. This reduces quiescent power consumption to just 48–100 mW in standby, versus >200 mW for single-supply SLICs-critical for Energy Star–compliant residential gateways. The B2EN pin controls this switching, and RTRIP2 enables VBAT1 re-engagement during non-ringing intervals.

What does the "-1" in LE79R79-1FQC indicate, and how does it affect performance?

The "-1" in LE79R79-1FQC denotes the performance grade: 52 dB longitudinal balance in normal polarity configuration. This grade meets LSSGR and FCC Part 68 requirements for North American short-loop CPE but does not support polarity reversal (unlike -2 grade). The "-1" suffix also confirms RoHS-compliant green packaging and QFN-32 tray delivery. Systems requiring ETSI-compliant 63 dB balance or polarity reversal must use LE79R79-2FQC instead.

Can the LE79R79-1FQC drive standard telephone ringers without external components?

Yes-the LE79R79-1FQC can drive standard telephone ringers directly using its integrated trapezoidal ringing generator. It delivers 66–69 Vpk into a 1570 Ω load (equivalent to five ringer equivalents per LSSGR), conditioned by a CMOS-compatible RINGIN square wave and an external RC shaping network. No external transformer or high-voltage amplifier is needed. However, RINGIN must be driven with 50% duty-cycle CMOS logic, and the RC network must be sized per the LE79R79 User's Guide (Doc #080914) to meet spectral mask requirements.

What thermal considerations apply to the LE79R79-1FQC in QFN-32 package?

The LE79R79-1FQC in QFN-32 relies on its exposed thermal pad-electrically connected to VBAT1-for heat dissipation. To achieve the specified 3.00 W max power dissipation at TA = 70°C, the pad must be soldered to an equally sized copper pour on the PCB, connected via ≥4 thermal vias to an internal ground or VBAT1 plane. Failure to implement this degrades θJA from 25°C/W to >40°C/W, risking thermal shutdown above 145°C junction temperature. The datasheet mandates IPC/JEDEC J-Std-020B reflow profile compliance.