Microchip Technology LE57D122BTCT

Overview

LE57D122BTCT from Zarlink Semiconductor is a dual-channel Subscriber Line Interface Circuit (SLIC) in 44-pin eTQFP package, supporting loop start and ground start telephony interfaces with –63 dB reverse polarity performance, programmable current limit, on-chip thermal management, and 2.0 Vrms metering capability for POTS line cards in India, China, Korea, Japan, Taiwan, Australia, and North America DLC applications.

For engineers reviewing the LE57D122BTCT datasheet, LE57D122BTCT pinout, LE57D122BTCT application, or LE57D122BTCT equivalent, this page delivers verified technical context, exact pin functions, real-world POTS deployment constraints, thermal management design implications, and validated alternative SLIC options for global line card designs requiring TR-57-CORE, GF002, G/LLT, or ITU Q.552 compliance.

Technical Context

The LE57D122BTCT integrates two fully independent SLIC channels into a single 44-pin eTQFP package, each supporting seven programmable states: Active, Active Metering, Reverse Polarity, Reverse Polarity Metering, Standby, Tip Open, and Disconnect. It implements per-channel off-hook detection, ring-trip detection, fault detection, and thermal shutdown with >145°C trip threshold and 10°C hysteresis.

Its two-wire interface delivers ≥20 mA loop current into 2000 Ω at –48 V, supports 2.0 Vrms metering via Active Metering states, and uses external TMG resistors (e.g., 1.8 kΩ) to offload power dissipation-reducing worst-case per-channel SLIC power to <1.6 W with both channels active. Control logic accepts 3.3-V–compatible inputs and powers up in Disconnect state.

Key Specifications

Pinout & Package

LE57D122BTCT is housed in a thermally enhanced 44-pin eTQFP (12 × 12 mm) package with exposed thermal pad connected to VBAT. The package supports high-density line card layouts and requires soldering the EPAD to PCB for optimal thermal performance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LE57D122BTCT, LE57D121BTC trades reverse polarity performance for cost, while LE5711 lacks thermal management-requiring larger heatsinking or derating. LE57D122BTCT uniquely balances high noise immunity, metering capability, and thermal efficiency in one package.

Availability

LE57D122BTCT is available at Aetrix Electronics and suitable for Central Office line cards, Digital Loop Carrier systems, and international POTS deployments requiring stable component supply, long-term lifecycle support, and RoHS-compliant green packaging.

Supply support for LE57D122BTCT 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.

The LE57D122BTCT belongs to Zarlink's VE580 Series of dual-channel SLIC devices, engineered specifically for high-density, low-power POTS line card applications across global telecom markets with diverse regulatory and environmental requirements.

FAQ

What is the reverse polarity specification of the LE57D122BTCT?

The LE57D122BTCT is specified for –63 dB reverse polarity rejection, enabling reliable operation in telecom environments where line polarity reversal occurs-such as in legacy wiring or multi-vendor interconnect scenarios. This value meets stringent regional requirements including those in Japan, Korea, and India, and exceeds the –53 dB rating of the LE57D121BTC variant. The specification is measured under standard test conditions per the official Zarlink datasheet.

How does the thermal management (TMG) feature work in the LE57D122BTCT?

The LE57D122BTCT uses dedicated TMG1 and TMG2 outputs to route excess power dissipation to external resistors connected between TMG pins and VBAT. For example, a 1.8 kΩ resistor limits worst-case per-channel SLIC power to under 1.6 W with both channels active. This offloads heat from the die, allowing sustained operation without thermal shutdown-even under high loop current and low resistance conditions. The TMG function is active in all Active states and is documented in Application Note 081110.

Does the LE57D122BTCT support pulse metering applications?

Yes, the LE57D122BTCT supports 2.0 Vrms pulse metering in Active Metering and Reverse Polarity Metering states, meeting requirements for 12 kHz and 16 kHz metering in India (G/LLT) and China (GF002). Its design includes increased overhead in these states to accommodate metering signal swing without clipping. The Pulse Metering Application Circuit on page 20 of the datasheet validates this capability using QLSLAC codecs and confirms compliance with ITU Q.552.

What are the key differences between LE57D122BTCT and LE57D121BTC?

The LE57D122BTCT and LE57D121BTC share identical 44-pin eTQFP packaging and core functionality but differ in reverse polarity performance: LE57D122BTCT is rated at –63 dB, while LE57D121BTC is rated at –53 dB. Both support metering and thermal management, but LE57D122BTCT targets higher-noise, longer-loop deployments. Neither is pin-compatible with non-Zarlink SLICs, and substitution requires validation against regional telecom standards.

What supply voltages does the LE57D122BTCT require?

The LE57D122BTCT requires two supplies: +5 V (VCC) for logic and control circuitry, and a negative battery supply (VBAT) ranging from –39 V to –60 V for line feeding. It supports optional dual battery operation to reduce total system power consumption. The device powers up in Disconnect state and accepts 3.3-V–compatible control inputs, making it interoperable with modern microcontrollers and SLAC devices without level-shifting.