Microchip Technology LE79R79-1DJCT

Overview

LE79R79-1DJCT 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), enabling compliance with LSSGR five-ringer equivalent specification in ISDN-TA and smart residential gateways.

For engineers reviewing the LE79R79-1DJCT datasheet, LE79R79-1DJCT pinout, LE79R79-1DJCT application, or LE79R79-1DJCT equivalent, this device supports critical SLIC BORSHT functions-including ring-trip detection, ground-key sensing, polarity reversal (enabled in -1 variant), and relay-driven line control-within a 32-pin PLCC green package meeting RoHS Directive 2002/95/EC.

Technical Context

The LE79R79-1DJCT implements a fully integrated analog front-end for two-wire telephone line interface, featuring dual battery selection logic (B2EN-controlled), programmable open-circuit voltage via RSGH/RSGL, and current gain of 1000 at RSN node. Its hybrid function is externally programmable via impedance network, and transhybrid balance achieves ≥52 dB longitudinal rejection in normal polarity mode.

It delivers trapezoidal ringing through CMOS-compatible RINGIN input with external RC shaping, supports on-hook transmission (OHT) with VTX output (0.5066× metallic AC voltage), and includes two open-collector relay drivers (RYOUT1/RYOUT2) with built-in 15 kΩ pull-up on DET output for supervision state decoding.

Key Specifications

Pinout & Package

LE79R79-1DJCT is housed in a 32-pin Plastic Leaded Chip Carrier (PLCC) green package with lead-free, halogen-free construction and matte-tin plating compatible with lead-free reflow profiles (peak ≤245°C). Pin 1 is marked for orientation; NC pins are not internally connected.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LE79R79-1DJCT, LE79R79-2DJC offers superior noise immunity but identical functionality otherwise, while LE79R100-1DJC trades battery-switching efficiency for greater ringing amplitude and thermal margin-making it suitable for harsher or longer-loop deployments.

Availability

LE79R79-1DJCT is available at Aetrix Electronics and suitable for ISDN-TA, smart residential gateways, fixed radio access units, and network interface units requiring stable component supply, RoHS-compliant packaging, and long-term lifecycle support.

Supply support for LE79R79-1DJCT 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 semiconductor company specializing in communications ICs, acquired by Microsemi in 2011 and later integrated into Microchip Technology. It pioneered high-integration SLIC solutions for global telephony infrastructure.

The LE79R79 belongs to Zarlink's VE580 Series of ringing SLICs, engineered specifically for cost-sensitive, space-constrained short-loop CPE applications including IADs, DSL modems, and voice gateways where on-chip ringing and dual-battery operation deliver system-level savings.

FAQ

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

The LE79R79-1DJCT serves as a complete Ringing Subscriber Line Interface Circuit (RSLIC), implementing all BORSHT functions-battery feed, overvoltage protection, ringing, supervision, hybrid, and test-for two-wire analog telephone line interfaces. In the LE79R79-1DJCT, on-chip trapezoidal ringing replaces external transformers, and dual-battery switching (VBAT1/VBAT2) optimizes power use across on-hook and off-hook states.

Does the LE79R79-1DJCT support polarity reversal, and how is it enabled?

Yes, the LE79R79-1DJCT supports polarity reversal as indicated by the "-1" suffix in its ordering code. This feature is implemented via internal switch matrix controlled by the C3–C1 decoder inputs and is active only when B2EN = 1 (VBAT1 selected). Polarity reversal enables compatibility with legacy test equipment and certain maintenance procedures requiring tip/ring swap.

How does the LE79R79-1DJCT achieve low standby power consumption?

The LE79R79-1DJCT achieves low standby power by automatically switching from high-voltage VBAT1 (–75 V) to low-voltage VBAT2 (–19 V) during off-hook operation using the B2EN control input. In standby (on-hook), it uses VBAT1 to meet open-circuit voltage requirements; in active state, it shifts to VBAT2, reducing quiescent power dissipation by over 50% compared to fixed-VBAT1 operation.

What external components are required to configure the LE79R79-1DJCT for standard 600 Ω line impedance?

To configure the LE79R79-1DJCT for 600 Ω line impedance, an external impedance network must be connected to the RSN pin, typically comprising two resistors and one capacitor forming a synthesized Z-line. The exact values are determined by the AC input impedance programming network shown in Figure 2 of the datasheet; no additional transformer or balun is needed due to the integrated hybrid function.

Can the LE79R79-1DJCT drive five telephone ringers simultaneously, and what design elements ensure compliance?

Yes, the LE79R79-1DJCT is specified to provide 66–69 Vpk ringing output into a 1570 Ω load, which satisfies the LSSGR five-ringer equivalent requirement. Compliance is ensured by its high open-circuit voltage capability (adjustable via RSGH), low-output-impedance power amplifiers (A(TIP)/B(RING)), and trapezoidal waveform shaping that meets spectral and crest-factor constraints defined in Telcordia GR-909.