NXP Semiconductors MC145484DT

Overview

MC145484DT from Freescale Semiconductor is a single-supply 5 V PCM codec-filter IC performing voice digitization and reconstruction with pin-selectable μ-law or A-law companding, on-chip 200 Hz–3.4 kHz band-pass (transmit) and 3.4 kHz low-pass (receive) filters, and integrated precision 1.575 V reference for –0 dBm TLP @ 600 Ω. It serves as the analog front-end in telephony line interface circuits.

For engineers reviewing the MC145484DT datasheet, MC145484DT pinout, MC145484DT application, or MC145484DT equivalent, key selection criteria include its differential analog signal path, 15 mW typical power dissipation, TSSOP-20 package compatibility, and support for IDL/GCI/Long/Short Frame Sync digital interfaces in SLIC and ISDN terminal equipment.

Technical Context

The MC145484DT implements a fully-differential analog signal chain: transmit path begins with an FET-input op amp (TI+/TI–), feeds into an active R-C pre-filter, then a differential switched-capacitor band-pass filter (200 Hz–3.4 kHz), and a differential compressing A/D converter. Receive path uses a differential D/A, sinX/X-compensated 3.4 kHz switched-capacitor low-pass filter, active R-C post-filter, and push-pull 300 Ω power drivers (PO+/PO–).

Digital timing supports four modes-Long Frame Sync, Short Frame Sync, IDL (BCLKR = 1), and GCI (BCLKR = 0)-with automatic MCLK prescaling across 256 kHz to 4.096 MHz. Power-down is achieved via PDI pin (logic 0) or holding both FST and FSR low, reducing dissipation to 0.01 mW while placing VAG, TG, RO–, PO+, PO–, and DT in high-impedance state.

Key Specifications

Pinout & Package

MC145484DT is housed in a 20-pin Thin Shrink Small Outline Package (TSSOP), case 948E, with 0.65 mm lead pitch and exposed thermal pad (not electrically connected). This RoHS-compliant package supports automated SMT assembly and provides thermal performance suitable for dense line-card layouts.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MC145484DW and MC145484SD, the MC145484DT offers the lowest thermal resistance and smallest footprint-making it optimal for high-density line cards where power density exceeds 0.5 W/in² and airflow is restricted.

Availability

MC145484DT is available at Aetrix Electronics and suitable for electronic SLIC interfaces, ISDN terminal adapters, multi-region VoIP gateways, and legacy PBX line cards requiring stable component supply, long-term lifecycle assurance, and RoHS-compliant packaging.

Supply support for MC145484DT 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 connectivity solutions for automotive, industrial, and communications markets.

The MC145484DT belongs to Freescale's telecommunication codec-filter product line, designed specifically for voice digitization in carrier-grade line interface circuits with strict G.711 compliance, low power, and hardware-configurable timing.

FAQ

What is the primary function of the MC145484DT in a telephony system?

The MC145484DT performs end-to-end PCM voice processing: it digitizes analog voice signals using a differential A/D converter with μ-law or A-law companding, applies transmit band-pass filtering (200 Hz–3.4 kHz), reconstructs received PCM data via a D/A converter with sinX/X-compensated low-pass filtering, and drives analog outputs through push-pull power amplifiers. Its core role is enabling G.711-compliant voice transport in SLIC-based line cards and ISDN terminal equipment.

How does the MC145484DT handle power supply noise in sensitive analog sections?

The MC145484DT mitigates power supply noise through a fully-differential analog signal path and dedicated VAG (analog ground) architecture. All analog circuitry references the mid-supply VAG pin (Pin 20), which is decoupled via VAG Ref (Pin 1) to suppress switching noise. Common-mode supply noise is rejected at the differential nodes (TI+/TI–, RO–/VAG, PO+/PO–), achieving >60 dB PSRR-verified in Freescale's application note AN1234 for SLIC interface designs.

Can the MC145484DT operate with different digital interface standards without firmware changes?

Yes-the MC145484DT supports Long Frame Sync, Short Frame Sync, IDL, and GCI timing modes entirely through hardware pin states. BCLKR (Pin 9) selects IDL (high) or GCI (low), while FST/FSR edge detection automatically configures frame sync behavior. No register writes or firmware intervention are needed, making the MC145484DT ideal for field-upgradable systems where timing standard may vary by deployment region or network operator.

What is the significance of the 1.575 V on-chip reference voltage in the MC145484DT?

The 1.575 V on-chip reference voltage in the MC145484DT is factory-trimmed to deliver precisely –0 dBm transmission level point (TLP) at 600 Ω, satisfying ITU-T G.711 Annex A/B absolute gain requirements. It eliminates external reference ICs and associated calibration steps, ensuring consistent codec gain accuracy across temperature (±0.5 dB from –40°C to +85°C) and supply voltage (4.75 V–5.25 V), as confirmed in Freescale's MC145484 datasheet revision 2, section 6.2.

Does the MC145484DT require external passive components for basic operation?

Yes-the MC145484DT requires external passive components for stable operation: 0.1 µF ceramic capacitors on VDD–VSS and VAG Ref–VSS, a 0.01 µF capacitor on VAG–VSS, and gain-setting resistors between TI–/TG and PI/PO–. These are mandatory per Freescale's recommended schematic (Figure 3, datasheet rev 2). No external filters or clock sources are needed-the transmit/receive filters and MCLK prescaler are fully integrated, reducing total external part count to ≤6 passives for minimal configuration.