Microchip Technology LE57D121BTC

Overview

LE57D121BTC 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 –39 to –60 V battery operation, programmable current limit, and on-chip thermal management. It delivers >20 mA into 2000 Ω from –48 V and supports 2.0 Vrms metering for POTS line cards in CO/DLC applications across North America, India, China, Japan, Korea, Taiwan, and Australia.

For engineers reviewing the LE57D121BTC datasheet, LE57D121BTC pinout, LE57D121BTC application, or LE57D121BTC equivalent, this page provides verified functional identity, dual-channel SLIC architecture, reverse polarity support (–53 dB), thermal shutdown per channel, low standby power (24 mW/channel), and RoHS-compliant green eTQFP packaging - all critical for telecom line card design and global regulatory compliance.

Technical Context

The LE57D121BTC integrates two fully independent SLIC channels into a single die, each with dedicated power feed controllers, off-hook/ground start detectors, ring-trip comparators, fault detectors, and thermal management outputs (TMG1/TMG2). Its two-wire interface supports Active, Reverse Polarity, Standby, Tip Open, and Disconnect states with programmable thresholds via external resistors RD and IREF.

It implements per-channel longitudinal fault detection using FLT1/FLT2 pins, thermal shutdown (>145°C, 10°C hysteresis), and DC feed regulation over 22–33 mA nominal current limit range. The device operates with +5 V logic supply (VCC) and –39 to –60 V battery supply (VBAT), with 3.3-V compatible control inputs and power-up default to Disconnect state.

Key Specifications

Pinout & Package

LE57D121BTC is housed in a 44-pin enhanced Thin Quad Flat Package (eTQFP), 12 mm × 12 mm, with exposed thermal pad (EPAD) that must be soldered to VBAT and PCB ground plane for thermal performance. Pin 1 marked; NC pins are unconnected. Package is RoHS-compliant, lead-free, halogen-free, and antimony-free.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LE57D122BTC, LE57D121BTC provides optimized reverse polarity for broader interoperability without over-engineering attenuation; compared with LE5711, it adds programmable current limit, thermal management, and flexible metering - enabling smaller, cooler, and more globally adaptable line cards.

Availability

LE57D121BTC is available at Aetrix Electronics and suitable for central office line cards, DLC remote terminals, ground start exchanges, and multi-market metering platforms requiring stable component supply, long-lifecycle support, and RoHS-compliant manufacturing.

Supply support for LE57D121BTC 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-performance SLIC and SLAC solutions for telecom infrastructure.

The LE57D121BTC belongs to Zarlink's VE580 Series of dual-channel SLIC devices, designed specifically for high-density, low-power POTS line cards requiring global regulatory compliance, programmable supervision, and thermal resilience in compact form factors.

FAQ

What is the primary function of the LE57D121BTC in a telecom line card?

The LE57D121BTC serves as a dual-channel Subscriber Line Interface Circuit (SLIC), providing battery feed, loop supervision (off-hook/ground start detection), ring-trip sensing, 2-wire audio interface, and programmable current limiting for two independent POTS subscriber lines. It replaces discrete SLIC implementations with integrated, thermally managed functionality in a single 44-pin eTQFP package.

Does the LE57D121BTC support both loop start and ground start signaling?

Yes, the LE57D121BTC natively supports both loop start and ground start signaling. Ground start operation is enabled in the Tip Open state, where the Ground Start Detector (GSD) monitors ring-to-ground current using the same RD-programmed threshold as the off-hook detector. Detection triggers automatic state transition to Active upon valid ground condition.

How does the thermal management (TMG) feature work in the LE57D121BTC?

The LE57D121BTC uses per-channel TMG1 and TMG2 outputs to drive external resistors (RTMG) connected to VBAT. During off-hook, this diverts significant power away from the die - reducing worst-case SLIC power dissipation to <1.6 W for both channels active. The minimum RTMG value depends on programmed current limit and loop resistance, with recommended values like 1.8 kΩ (5%) for BATMAX = –56 V and ILIMITMIN = 30 mA.

What are the key differences between LE57D121BTC and LE57D122BTC?

The LE57D121BTC and LE57D122BTC share identical architecture, pinout, and package but differ in reverse polarity attenuation: LE57D121BTC provides –53 dB, while LE57D122BTC delivers –63 dB. Both support the same battery range (–39 to –60 V), current capability (>20 mA), and thermal management features. Selection depends on system-level echo return loss requirements.

Can the LE57D121BTC operate with a single battery supply or does it require dual battery configuration?

The LE57D121BTC is designed for single –39 to –60 V battery operation but supports optional dual battery configuration to reduce total power consumption. In dual battery mode, one battery powers the analog section while the other supplies bias, allowing dynamic power scaling - though external circuitry and control logic are required to manage switching and sequencing.