NXP Semiconductors MC145481EN

Overview

MC145481EN from Freescale Semiconductor is a single-supply, 20-pin PCM codec-filter IC performing simultaneous voice digitization (A/D) and reconstruction (D/A), with on-chip transmit band-pass (200 Hz–3.4 kHz) and receive low-pass (3.4 kHz) filtering, pin-selectable μ-law or A-law companding, and integrated 0.886 V precision reference for –5 dBm TLP at 600 Ω. It targets telephony line interface cards and ISDN terminal adapters.

For engineers reviewing the MC145481EN datasheet, MC145481EN pinout, MC145481EN application, or MC145481EN equivalent, this device supports synchronous/asynchronous operation across IDL, GCI, Long/Short Frame Sync timing modes, delivers 8 mW typical power dissipation at 3 V, and integrates fully-differential analog signal paths to achieve high PSRR and low noise in voice-band systems.

Technical Context

The MC145481EN implements a differential switched-capacitor architecture: its encoder path includes active R-C pre-filtering, single-ended-to-differential conversion, 5-pole low-pass (3.4 kHz), and 3-pole high-pass (~200 Hz) filtering before a differential compressing A/D converter. The decoder path uses a differential D/A, sinX/X-compensated 5-pole switched-capacitor low-pass filter, and active R-C post-filtering.

It features a high-impedance VAG reference pin decoupled from VSS, enabling clean analog grounding when external signals are referenced to power supply ground; clock inputs (MCLK, FST, BCLKT, FSR, BCLKR) support automatic prescaling across 256 kHz–4.096 MHz and four industry-standard PCM interface modes without external configuration logic.

Key Specifications

Pinout & Package

MC145481EN is packaged in a 20-pin SOG (Small Outline Gull-wing, Case 751D) with 0.65 mm pitch and standard JEDEC MO-153 footprint. Pin assignments are validated per Freescale Semiconductor Technical Data Sheet MC145481/D (Rev 2, Nov 1998).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MC145481EN, MC145503DW trades integrated 300 Ω drivers and differential noise immunity for lower quiescent power, while TP3067CP sacrifices flexibility, PSRR, and modern supply range to maintain pinout compatibility with obsolete 5 V designs - making MC145481EN the optimal choice for new 3 V telephony hardware requiring robust analog performance and ISDN readiness.

Availability

MC145481EN is available at Aetrix Electronics and suitable for telephony line cards, ISDN terminal adapters, VoIP gateway FXS ports, and digital PBX interfaces requiring stable component supply, long-term lifecycle assurance, and traceable sourcing from authorized channels.

Supply support for MC145481EN 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

Freescale Semiconductor (now part of NXP Semiconductors) is a fabless semiconductor company specializing in embedded processing, analog, and mixed-signal solutions for automotive, industrial, and communications markets.

The MC145481EN belongs to Freescale's telecommunication codec portfolio, designed specifically for carrier-grade voice digitization in PSTN, ISDN, and early VoIP infrastructure - emphasizing low-noise differential analog design, multi-standard digital interface flexibility, and precise ITU-T G.711 compliance.

FAQ

What is the function of the VAG and VAG Ref pins on the MC145481EN?

The VAG pin (Pin 20) provides a mid-supply analog ground reference (VDD/2) for all internal analog circuitry, and must be decoupled to VSS with a 0.01 µF capacitor. The VAG Ref pin (Pin 1) bypasses the internal VAG generator circuitry and requires a 0.1 µF capacitor to VSS using short, low-inductance traces. In MC145481EN, these pins enable separation of analog and digital ground domains, reducing clock-induced noise on the analog signal path - critical for achieving <0.5% THD+N in voice-band applications.

Does the MC145481EN support both μ-law and A-law companding simultaneously?

No, the MC145481EN supports μ-law or A-law companding exclusively - selected by the logic level on Pin 16 (Mu/A). When Mu/A = VDD, the encoder applies μ-law compression and the decoder performs μ-law expansion; when Mu/A = VSS, both encode and decode use A-law. This pin-selectable behavior is hardwired and cannot be changed dynamically during operation - the MC145481EN does not support dual-law or software-switchable companding.

Can the MC145481EN operate with a 3.3 V supply, and what is its power consumption at that voltage?

Yes, the MC145481EN operates across 2.7 V to 5.25 V, and its typical power dissipation at 3.3 V is 8.5 mW (within datasheet-specified 8 mW @ 3 V tolerance). In power-down mode (PDI = low), consumption drops to 0.01 mW. This makes MC145481EN suitable for 3.3 V telephony systems without level shifters or regulators, while maintaining full G.711 compliance and 300 Ω line-driving capability.

What digital interface modes does the MC145481EN support, and how are they configured?

The MC145481EN supports four modes: Long Frame Sync, Short Frame Sync, IDL, and GCI - configured via BCLKR (Pin 9) and timing relationships among FST, FSR, BCLKT, and BCLKR. BCLKR = high selects IDL; BCLKR = low selects GCI; Frame Sync modes are auto-detected based on pulse width relative to BCLKT. All modes use standard 8-bit serial PCM data aligned to FST/FSR edges, and MC145481EN requires no external configuration registers or firmware to switch between them.

How does the MC145481EN handle power-down, and what pins go high-impedance?

The MC145481EN enters power-down either via PDI (Pin 10) = low or by holding both FST and FSR low for ≥2 consecutive 8 kHz frames. In this state, RO–, PO+, PO–, TG, DT, and VAG become high-impedance; VAG Ref is pulled to VDD via a nonlinear high-impedance circuit. The device retains its Mu/A selection and internal reference bias but halts all clocking and analog signal processing - resuming normal operation within two FST cycles after PDI returns high and valid frame sync resumes.