Analog Devices Inc./Maxim Integrated MAX9945AUA+T

Overview

The MAX9945AUA+T from Maxim Integrated is a precision MOS-input operational amplifier optimized for low-noise, low-power analog front-ends in photodiode transimpedance and chemical sensor interfaces. It delivers 15nV/√Hz input voltage noise, 1fA/√Hz input current noise, 400µA quiescent current, rail-to-rail output swing, and 3MHz unity-gain bandwidth - enabling high-fidelity signal conditioning in portable medical pulse oximeters and industrial pH sensors.

For engineers reviewing the MAX9945AUA+T datasheet, MAX9945AUA+T pinout, MAX9945AUA+T application, or MAX9945AUA+T equivalent, this page provides verified technical context, package-specific pin mapping, real-world application constraints, and validated alternative options for sensor interface design under tight power and noise budgets.

Technical Context

The MAX9945AUA+T employs a BiCMOS process with MOS input stage to achieve 50fA typical input bias current and ultra-low 1fA/√Hz input current noise - critical for high-impedance current-source sensors like photodiodes. Its rail-to-rail output stage swings within 50mV of either supply rail under 100kΩ load while maintaining stability with up to 120pF capacitive load.

It operates from ±2.4V to ±19V dual supply or +4.75V to +38V single supply, supports common-mode input range from VEE to VCC − 1.2V, and features 130dB open-loop gain (typ) and 82dB PSRR - enabling high-gain, DC-accurate amplification in battery-powered instrumentation without external level-shifting.

Key Specifications

Pinout & Package

The MAX9945AUA+T is packaged in an 8-pin µMAX® (U8+1) package, measuring 3mm × 3mm × 0.8mm with exposed thermal pad not present in this variant. Pin 1 is located at the top-left corner when the marking dot is oriented top-left; pins are numbered counterclockwise.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar low-noise, low-power op amp applications.

Compared with OPA377AIDBVR and ADA4522-1ARMZ, the MAX9945AUA+T uniquely combines 38V operation, femtoamp input bias, and sub-1fA/√Hz current noise - making it irreplaceable in high-impedance, high-supply, low-power sensor front-ends where all three parameters are simultaneously required.

Availability

The MAX9945AUA+T is available at Aetrix Electronics and suitable for portable medical diagnostics, industrial chemical sensing, automotive cabin air quality monitoring, and battery-powered instrumentation requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for MAX9945AUA+T 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 power-management ICs for industrial, medical, and automotive applications.

The MAX9945AUA+T belongs to Maxim's precision op amp product line, designed specifically for low-noise, low-power sensor signal conditioning in harsh environments where wide supply range and femtoamp input bias are mandatory.

FAQ

What is the maximum capacitive load the MAX9945AUA+T can drive without instability?

The MAX9945AUA+T is specified to remain stable with up to 120pF capacitive load across its full operating temperature range (−40°C to +125°C). This eliminates the need for series isolation resistors in most photodiode transimpedance configurations, preserving bandwidth and minimizing noise contribution. For loads exceeding 120pF, external compensation or a dedicated buffer stage is required. The MAX9945AUA+T datasheet confirms no sustained oscillations occur at this limit under worst-case process and temperature conditions.

Does the MAX9945AUA+T support true rail-to-rail input common-mode range?

No, the MAX9945AUA+T does not support rail-to-rail input. Its input common-mode voltage range extends from VEE to VCC − 1.2V (typ) at +25°C, and to VCC − 1.4V over full temperature range. This means the noninverting and inverting inputs cannot accept signals within 1.2V of VCC. However, the output achieves rail-to-rail swing - delivering voltages within 50mV of both supply rails under 100kΩ load. The MAX9945AUA+T is therefore ideal for output-stage buffering but requires input biasing for high-side signal handling.

Can the MAX9945AUA+T operate from a single 5V supply in portable medical devices?

Yes, the MAX9945AUA+T operates from a minimum single-supply voltage of +4.75V, making it fully compatible with standard 5V LDO-regulated or USB-powered portable medical devices. At 5V supply, it maintains 400µA quiescent current, 15nV/√Hz voltage noise, and rail-to-rail output swing - enabling high-resolution analog front-ends in compact pulse oximeters and handheld biosensors without compromising battery life or signal fidelity. The MAX9945AUA+T's −40°C to +125°C rating further ensures reliability in variable ambient conditions.

What is the purpose of the unconnected pins (1, 5, 8) on the MAX9945AUA+T µMAX package?

Pins 1, 5, and 8 on the MAX9945AUA+T are internally unconnected (N.C.) and serve no functional role in the amplifier circuit. However, Maxim recommends connecting them to analog ground or a driven guard potential - especially Pin 1 adjacent to IN− - to reduce parasitic leakage currents in high-impedance transimpedance applications. This practice improves DC accuracy and long-term stability when interfacing with photodiodes or pH electrodes. The MAX9945AUA+T datasheet explicitly cites this layout technique to suppress leakage-induced offset drift.

How does the MAX9945AUA+T compare to the MAX9945ATT+ in terms of thermal performance?

The MAX9945AUA+T (8-pin µMAX) has a junction-to-ambient thermal resistance (θJA) of 206.3°C/W, significantly higher than the MAX9945ATT+ (6-pin TDFN-EP) at 42°C/W due to the absence of an exposed thermal pad. As a result, the MAX9945AUA+T dissipates heat less efficiently and requires careful PCB layout - including generous copper pour on the VEE-connected layer - to maintain junction temperature below +150°C under 400µA quiescent load. The MAX9945AUA+T is best suited for moderate ambient temperatures (<+85°C) or low-duty-cycle applications where peak power dissipation remains below 10mW.