Microchip Technology LE7942BDJCT

Overview

LE7942BDJCT from Zarlink Semiconductor is a Subscriber Line Interface Circuit (SLIC) designed for PBX and Key Telephone System (KTS) applications. It delivers programmable constant-current feed, –19 V to –58 V battery operation, 500× receive current gain, on-chip switching regulator for low-power dissipation, and ground-key detection with dedicated GKFIL pin for external noise-filter capacitor.

For engineers reviewing the LE7942BDJCT datasheet, LE7942BDJCT pinout, LE7942BDJCT application, or LE7942BDJCT equivalent, this device supports precise loop-current programming via RDC network, polarity reversal, tip-open state for ground-start lines, and dual relay drivers (RINGOUT/TESTOUT) with zener clamping - critical for telephony linecard design and legacy voice infrastructure.

Technical Context

The LE7942BDJCT integrates a high-voltage analog front-end with digital control logic, supporting both active and off-hook transmission modes. Its SLIC architecture includes a 500× transimpedance amplifier at RSN, programmable loop-detect threshold via RD resistor, and chopper-stabilized switching regulator (CHCLK = 256 kHz typical) with L-pin transistor output.

It implements configurable detector selection (C3–C1/E1) for off-hook, ring-trip, or ground-key states, with DET output providing open-collector logic-level indication. The device operates across –19 V to –58 V battery supply while maintaining <100 mW on-hook power dissipation when using the internal switching regulator.

Key Specifications

Pinout & Package

LE7942BDJCT is housed in a 32-pin Plastic Leaded Chip Carrier (PLCC) package with thermal pad (TP) tied internally to QBAT. Pin 1 is marked for orientation; TP serves as heat dissipation path and may be left open or connected to QBAT.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LE7942BDJCT, LE7942B–1DJC extends operational reliability to –40°C, while LE7942BDJC retains RoHS compliance without temperature grade - enabling trade-offs between environmental robustness, regulatory compliance, and BOM cost in telephony hardware design.

Availability

LE7942BDJCT is available at Aetrix Electronics and suitable for Central Office Line Cards, Enterprise PBX Interfaces, and Key Telephone Systems requiring stable component supply, long lifecycle support, and traceable sourcing for telecom infrastructure programs.

Supply support for LE7942BDJCT 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 (acquired Legerity's SLIC portfolio in August 2007) is a fabless semiconductor company specializing in communications ICs, particularly voice and timing solutions for telecom infrastructure.

The LE7942BDJCT belongs to the VE580 Series SLIC family, engineered specifically for high-reliability analog line interface in PBX, KTS, and central office equipment - emphasizing low standby power, programmable feed, and integrated relay control.

FAQ

What is the primary function of the LE7942BDJCT in a telephony system?

The LE7942BDJCT serves as a Subscriber Line Interface Circuit (SLIC) that manages analog telephone line interface functions including battery feed, loop supervision, ringing, polarity reversal, and hybrid two-wire/four-wire conversion. In the LE7942BDJCT, these functions are implemented with programmable constant-current feed, 500× receive gain, and integrated relay drivers - making it essential for PBX, KTS, and central office linecards.

Does the LE7942BDJCT require an external switching regulator, or does it include one?

The LE7942BDJCT includes an on-chip switching regulator with CHCLK input (256 kHz typical) and L-pin transistor output, enabling low-power dissipation in battery-fed systems. It can also operate without the switching regulator by connecting L, CHS, and VREG to VBAT and CHCLK to AGND/DGND - giving designers flexibility based on thermal and layout constraints in the final LE7942BDJCT implementation.

How does the ground-key detection feature work on the LE7942BDJCT?

Ground-key detection on the LE7942BDJCT is enabled via the E1 input and uses the B(RING) line referenced to ground. When E1 = High, the ground-key detector connects to the DET output. A dedicated GKFIL pin requires a minimum 3300 pF capacitor to AGND/DGND to suppress noise - ensuring reliable detection of ground-start signaling in KTS and PBX trunk interfaces using the LE7942BDJCT.

What are the key thermal considerations for the LE7942BDJCT in high-density linecards?

The LE7942BDJCT features a thermal pad (TP) internally tied to QBAT, which must be connected to copper pour for effective heat dissipation. Its maximum power dissipation is 1.74 W in the 32-pin PLCC package, with thermal limiting shutting down the device at ~165°C junction temperature. For sustained operation, keep junction temperature below 145°C - especially critical when using the on-chip switching regulator in the LE7942BDJCT under –48 V battery conditions.

Can the LE7942BDJCT support both normal and reverse polarity line states?

Yes, the LE7942BDJCT supports polarity reversal in both Active and OHT states, selectable via C3–C1 control inputs (Table 1). This allows the device to drive reversed line polarity for specific signaling protocols or fault recovery - confirmed by longitudinal balance measurements of ≥52 dB across 200 Hz–3.4 kHz in both polarities, as specified in the LE7942BDJCT datasheet.