Analog Devices Inc./Maxim Integrated MAX121EWE+

Overview

The MAX121EWE+ from Maxim Integrated is a 14-bit, 308ksps successive-approximation analog-to-digital converter (ADC) with integrated track/hold, ±5V bipolar input range, -5V buried-zener reference, and TTL/CMOS-compatible serial interface optimized for DSP interfacing. It operates from +5V and -12V/-15V supplies, consumes 210mW, and delivers 77dB SINAD at -40°C to +85°C - used in real-time audio digitization and telecom channel sampling.

For engineers reviewing the MAX121EWE+ datasheet, MAX121EWE+ pinout, MAX121EWE+ application, or MAX121EWE+ equivalent, this page provides verified electrical parameters, mode-specific timing behavior, DSP interface compatibility (TMS320, ADSP2101, µPD77230), acquisition time constraints, and validated alternative parts for signal chain design.

Technical Context

The MAX121EWE+ implements a BiCMOS SAR architecture with on-chip track/hold and low-drift -5V zener reference, enabling precise 14-bit conversion without external calibration. Its three operational modes - CONVST-triggered (Mode 1), CS-triggered (Mode 2), and continuous-conversion (Mode 3) - support deterministic sampling control or high-throughput streaming into FIFO/DMA buffers.

It features dual framing outputs (SFRM and FSTRT), programmable clock polarity inversion (INVCLK/INVFRM), and two's-complement 16-bit serial output (14 data bits + 2 trailing zeros) synchronized to CLKIN rising edges. All digital I/Os meet TTL/CMOS voltage thresholds, and the analog input presents 6kΩ || 10pF impedance with 400ns acquisition time.

Key Specifications

Pinout & Package

MAX121EWE+ is housed in a 20-pin SSOP (Shrink Small Outline Package) with 0.65mm pitch, JEDEC MO-153 compliant, footprint compatible with space-constrained PCB layouts in portable test equipment and embedded DSP modules.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 14-bit, DSP-interfaced ADC applications.

Compared with ADS8322IPFB and AD7865BSZ-1, the MAX121EWE+ uniquely combines 308ksps throughput, built-in SFRM/FSTRT framing, and -5V reference in a single 20-pin SSOP - reducing BOM count and layout complexity in DSP-centric designs requiring deterministic timing.

Availability

MAX121EWE+ is available at Aetrix Electronics and suitable for audio digitization, telecom channel sampling, and DSP servo control applications requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for MAX121EWE+ 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) designs precision analog, mixed-signal, and high-speed data conversion ICs for demanding industrial, communications, and computing applications.

The MAX121EWE+ belongs to Maxim's high-speed precision ADC product line, engineered specifically for seamless integration with digital signal processors in real-time acquisition systems - emphasizing low-latency serial interfaces, on-chip references, and robust operation across -40°C to +85°C.

FAQ

What is the maximum clock frequency supported by the MAX121EWE+ in continuous-conversion mode?

The MAX121EWE+ supports a maximum clock frequency of 5MHz in continuous-conversion mode (Mode 3). This limit ensures the 400ns minimum acquisition time is met within two clock cycles. At 5MHz, the device achieves 312.5ksps throughput (16 clock cycles per conversion). Exceeding 5MHz violates the acquisition timing specification and risks missing codes or degraded SINAD performance. The datasheet confirms this constraint applies only to Mode 3; Modes 1 and 2 allow up to 5.5MHz.

How does the MAX121EWE+ interface with the ADSP2101 DSP, and what pins are required?

The MAX121EWE+ interfaces directly with the ADSP2101 using four dedicated connections: SFRM → RFS (frame sync), SDATA → DR (data receive), SCLK → SCLK (clock input), and CONVST → an output port (conversion trigger). INVFRM must be grounded to align SFRM polarity with ADSP2101's RFS active-low requirement. No external logic or level shifters are needed. This configuration leverages the MAX121EWE+'s native framing to achieve deterministic 5.5MHz operation - matching the ADSP2101's maximum serial interface speed.

What is the purpose of the INVCLK and INVFRM pins on the MAX121EWE+, and how should they be configured?

The INVCLK pin inverts the phase of the SCLK output relative to CLKIN, while INVFRM inverts the polarity of the SFRM output. Both are logic-level inputs tied to VDD (no inversion) or DGND (inversion). They enable direct compatibility with diverse serial standards: e.g., grounding INVFRM makes SFRM active-low for ADSP2101 RFS, and tying INVCLK to DGND flips SCLK for QSPI CPHA=0 configurations. These pins eliminate external inverters, simplifying PCB layout and reducing signal path skew in high-speed interfaces.

Can the MAX121EWE+ operate with an external reference voltage, and what are the requirements?

Yes, the MAX121EWE+ accepts an external reference voltage applied to the VREF pin, provided it falls within -5.05V to -5.10V and can sink ≥5mA. The internal -5V zener reference is overdriven in this configuration. External bypassing (22µF || 0.1µF) remains mandatory to maintain noise performance. Using an external reference is appropriate when higher initial accuracy (<±0.05%) or lower temperature drift (<±10ppm/°C) is required beyond the internal reference's ±0.2% full-scale error and ±30ppm/°C drift.

What are the key differences between Mode 1, Mode 2, and Mode 3 operation of the MAX121EWE+?

Mode 1 uses CONVST to trigger conversions (MODE = VDD, CS = DGND) - ideal for precise timestamped sampling in DSP systems. Mode 2 uses CS to trigger and enable outputs (MODE = VDD, CONVST = DGND) - suited for shared serial buses where high-Z outputs prevent contention. Mode 3 (MODE = DGND, CONVST = CS = DGND) runs continuously at 1/16th the CLKIN frequency - optimized for streaming into FIFO/DMA without software intervention. Each mode imposes distinct timing constraints: Mode 3 caps CLKIN at 5MHz; Modes 1/2 allow up to 5.5MHz.