NXP Semiconductors MC145481DT

Overview

MC145481DT from Freescale Semiconductor is a single-channel PCM codec-filter IC performing 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 operates from a single 2.7–5.25 V supply with 8 mW typical dissipation and supports synchronous/asynchronous timing including IDL, GCI, Short/Long Frame Sync.

For engineers reviewing the MC145481DT datasheet, MC145481DT pinout, MC145481DT application, or MC145481DT equivalent, this device serves as a drop-in-ready telephony interface solution requiring no external filters or reference components, compatible with Motorola/Freescale U/S/T-interface transceivers and SLICs, and validated for ISDN terminal equipment, channel banks, and digital PBX line cards.

Technical Context

The MC145481DT implements a fully differential analog signal path: input op-amp (TI+/TI–) drives a differential switched-capacitor anti-aliasing filter (200 Hz–3.4 kHz), followed by a differential compressing A/D converter using successive-approximation architecture with shared CDAC/RDAC and autozeroed comparator. The receive path uses the same DAC core, sinX/X-compensated 3.4 kHz low-pass switched-capacitor filter, active R-C smoothing, and differential push-pull power drivers (PO+/PO–).

Digital interface flexibility is achieved via four timing modes (Long/Short Frame Sync, IDL, GCI) selected by BCLKR logic state and frame sync alignment; MCLK accepts 256 kHz–4.096 MHz with automatic prescaling to generate internal 256 kHz sequencing clock; power-down is supported via PDI pin or FST/FSR hold-low, placing VAG, DT, RO–, TG, PO+/PO– in high-impedance state.

Key Specifications

Pinout & Package

MC145481DT is packaged in 20-pin SOG (Small Outline Gull-wing, Case 751D), with 0.65 mm lead pitch and standard JEDEC MS-013 footprint. Pin assignments are identical to MC145481DW variant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MC145481DW, the MC145481DT offers identical core functionality in a commercial-grade SOG package with tighter manufacturing tolerances, while TP3067CP requires external reference and clock generation, increasing BOM count and reducing system-level accuracy.

Availability

MC145481DT is available at Aetrix Electronics and suitable for ISDN terminal adapters, digital line cards, channel bank interfaces, and VoIP gateway FXS ports requiring stable component supply, long-term lifecycle support, and G.711-compliant voice digitization.

Supply support for MC145481DT 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 MC145481DT belongs to Freescale's legacy telecommunication codec family, designed specifically for carrier-grade voice digitization in TDM-based infrastructure where pin compatibility, analog performance stability, and multi-standard timing support are critical.

FAQ

What is the primary function of the MC145481DT in a telephony system?

The MC145481DT serves as a complete single-channel PCM codec-filter, performing analog-to-digital conversion (A/D) with μ-law or A-law companding, digital-to-analog conversion (D/A) with expansion, and integrated transmit band-pass (200 Hz–3.4 kHz) and receive low-pass (3.4 kHz) filtering. It replaces discrete op-amps, filters, and references in voice digitization paths for ISDN, PBX, and channel bank applications. Its on-chip 0.886 V reference ensures precise –5 dBm transmission level point calibration without external components.

Does the MC145481DT require external clock sources or can it operate with internal timing?

The MC145481DT requires an external master clock (MCLK) applied to Pin 11, but supports frequencies from 256 kHz to 4.096 MHz with automatic internal prescaling to generate the required 256 kHz sequencing clock. It does not contain an internal oscillator. Frame sync (FST/FSR) and bit clock (BCLKT/BCLKR) must also be supplied externally, though MCLK may be tied to BCLKT in many implementations. No crystal or external PLL is needed beyond these three clock inputs.

How does the MC145481DT handle analog grounding when external signals are referenced to VSS?

The MC145481DT uses a dedicated high-impedance VAG (Pin 20) output as its internal analog ground reference. When external analog signals are referenced to VSS, the VAG Ref (Pin 1) bypass capacitor and careful PCB layout - including short, low-inductance traces and separation of analog/digital ground planes - are required to minimize noise coupling between VSS and VAG. The device's differential architecture inherently rejects common-mode noise on the VSS rail, preserving SNR in mixed-ground systems.

Can the MC145481DT drive a standard telephone line directly?

No, the MC145481DT cannot drive a standard POTS telephone line directly. Its PO+/PO– outputs deliver +7 dBm into a 300 Ω balanced load, suitable for line interface circuits like SLICs (e.g., MC3419) or transformer-coupled hybrid networks. Direct connection to a 600 Ω tip/ring line would violate impedance matching, exceed voltage swing limits, and lack battery feed, ring detection, and off-hook supervision - functions handled by dedicated line interface ICs.

What happens to the DT, RO–, and PO+/PO– pins during power-down mode?

When the MC145481DT enters power-down mode - either via logic-low PDI (Pin 10) or by holding both FST and FSR low - the DT (Pin 13), RO– (Pin 2), and PO+/PO– (Pins 4–5) outputs transition to high-impedance state. This prevents bus contention on shared PCM data lines and avoids loading downstream analog stages. Simultaneously, VAG (Pin 20) and TG (Pin 17) also go high-Z, while VAG Ref (Pin 1) is pulled to VDD through a nonlinear high-impedance circuit.