Analog Devices Inc./Maxim Integrated MAX9476EUG

Overview

MAX9476EUG from Maxim Integrated is a low-jitter, 8kHz reference clock synthesizer IC that generates six buffered LVTTL outputs at 35.328MHz and one jitter-suppressed 8kHz reference relay output (REO), using an external 35.328MHz VCXO crystal locked to the 8kHz input reference. It operates from +3.0V to +3.6V over -40°C to +85°C and targets telecom timing in T1/E1/T3/E3/xDSL systems.

For engineers reviewing the MAX9476EUG datasheet, MAX9476EUG pinout, MAX9476EUG application, or MAX9476EUG equivalent, key selection criteria include its ±100ppm reference lock range, 4psRMS typical output jitter, six identical LVTTL clock outputs with ≤185ps peak-to-peak skew, REO jitter suppression capability, and 24-pin TSSOP package compatibility with telecom board layouts.

Technical Context

The MAX9476EUG implements a PLL-based architecture with an integrated voltage-controlled crystal oscillator (VCXO) that phase-locks a 35.328MHz fundamental-mode crystal to an 8kHz reference input (REIN) via a programmable charge-pump loop filter (LP1/LP2/SETI). The PLL divider ratio is fixed at 4416, enabling precise frequency synthesis.

It features internal reference clock monitoring that detects loss of REIN by counting low-to-high transitions over three 8kHz cycles, automatically switching outputs to crystal center frequency upon loss and relocking when REIN returns. All six CLK outputs are LVTTL-compliant with VOH ≥ VDD–0.6V and VOL ≤ 0.4V at ±4mA, and share tight skew control (≤185ps p-p).

Key Specifications

Pinout & Package

MAX9476EUG is housed in a 24-pin Thin Shrink Small Outline Package (TSSOP) with 0.65mm lead pitch and 4.4mm body width, optimized for high-density telecom PCB layouts and thermal dissipation up to 976mW at +70°C ambient.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar clock synthesizer applications.

Compared with MAX9486EUG and ICS843002AGI-01LFT, the MAX9476EUG uniquely combines integrated VCXO, jitter-suppressed REO, reference monitoring, and six LVTTL outputs in a compact TSSOP-making it the most direct solution for cost-sensitive, space-constrained T1/E1/xDSL timing where crystal-based stability and telecom-grade reliability are mandatory.

Availability

MAX9476EUG is available at Aetrix Electronics and suitable for T1/E1 line cards, E3/T3 multiplexers, xDSL central office equipment, and ISDN network termination units requiring stable component supply, long-term lifecycle support, and guaranteed traceable sourcing.

Supply support for MAX9476EUG 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

Maxim Integrated (now part of Analog Devices) is a semiconductor company specializing in high-performance analog, mixed-signal, and precision timing solutions for communications, industrial, and computing markets.

The MAX9476EUG belongs to Maxim's telecom clock synthesizer product line, designed specifically to replace discrete crystal oscillators and PLLs in carrier-grade T1/E1/xDSL timing applications while meeting stringent jitter, lock range, and reliability requirements.

FAQ

What is the primary function of the MAX9476EUG in telecom systems?

The MAX9476EUG serves as a low-jitter clock synthesizer that generates six synchronized 35.328MHz LVTTL clock outputs and one jitter-suppressed 8kHz reference relay output (REO) for T1, E1, T3, E3, and xDSL equipment. Its core function is to phase-lock an external 35.328MHz VCXO crystal to an 8kHz telecom reference input, ensuring precise, stable timing across multiple channels while rejecting input jitter. This makes the MAX9476EUG essential for maintaining bit-error-rate compliance and frame alignment in carrier-class infrastructure.

Does the MAX9476EUG require an external crystal, and what specifications must it meet?

Yes, the MAX9476EUG requires an external 35.328MHz fundamental-mode AT-cut quartz crystal connected between pins X1 and X2. Per the datasheet, the crystal must have ±25ppm total frequency accuracy (including initial tolerance and temperature drift over –40°C to +85°C) and a load capacitance of 14pF. Using a crystal outside these specs risks reduced pulling range, increased output phase jitter, or failure to lock-so the MAX9476EUG's performance is directly dependent on correct crystal selection and layout per the recommended 0.1µF + 0.001µF bypassing at VDDP/GNDP.

How does the MAX9476EUG handle loss of the 8kHz reference input (REIN)?

The MAX9476EUG includes an internal reference clock monitor that continuously checks REIN for low-to-high transitions over three 8kHz cycles. If fewer than two transitions are detected, it declares REIN lost and automatically switches all CLK1–CLK6 outputs to the center frequency of the 35.328MHz crystal oscillator. When REIN returns, the PLL relocks seamlessly. This failover behavior ensures uninterrupted clocking-critical for telecom systems where reference loss must not cause service interruption-and is intrinsic to the MAX9476EUG's architecture, requiring no external supervision.

What is the purpose of the LP1, LP2, and SETI pins on the MAX9476EUG?

LP1 and LP2 form the connection points for the external PLL loop filter (typically R1, C1, C2), which determines the bandwidth and damping of the VCXO control loop. SETI sets the PLL charge-pump current via an external resistor to GNDP, allowing designers to tune loop dynamics-e.g., a 13kΩ resistor yields ~182µA, optimizing lock time versus jitter rejection. These pins give full control over the MAX9476EUG's PLL response, enabling customization for specific application needs such as fast lock after power-up or maximum jitter attenuation on noisy reference inputs.

Can the MAX9476EUG operate from a 3.3V supply, and what are the supply current requirements?

Yes, the MAX9476EUG operates from a single +3.0V to +3.6V supply, with typical performance specified at +3.3V. Total supply current (IDD + IDDP) is 9mA (min) to 16mA (max) under normal operation with no load on clock outputs; shutdown current drops to 7.5µA (typ) when SHDN is driven low. Both VDD (digital) and VDDP (PLL analog) rails must be independently bypassed with 0.1µF and 0.001µF capacitors to their respective grounds (GND and GNDP) to ensure stable operation and minimal jitter-this dual-supply design is integral to the MAX9476EUG's noise immunity.