Texas Instruments LMP7721MAX/NOPB

Overview

LMP7721MAX/NOPB from Texas Instruments is an ultra-low-input-bias-current precision operational amplifier designed for high-impedance sensor signal conditioning. It delivers ±20 fA max input bias current at 25°C, 120 dB DC open-loop gain, and 17 MHz gain-bandwidth product while operating from 1.8 V to 5.5 V supply - enabling accurate photodiode and ion chamber amplification in battery-powered instrumentation.

For engineers reviewing the LMP7721MAX/NOPB datasheet, LMP7721MAX/NOPB pinout, LMP7721MAX/NOPB application, or LMP7721MAX/NOPB equivalent, key selection criteria include verified fA-level input bias stability across −40°C to 125°C, rail-to-rail output swing within 20 mV of rails at 10 kΩ load, and SOIC-8 pin isolation architecture that minimizes PCB leakage coupling into IN+ and IN−.

Technical Context

The LMP7721MAX/NOPB employs patented input bias current cancellation circuitry to maintain ≤±20 fA bias over full common-mode voltage range (−0.3 V to 4 V at 5 V supply), independent of temperature-induced leakage drift. Its MOS input stage yields 0.01 pA/√Hz input current noise and 6.5 nV/√Hz voltage noise at 1 kHz.

This architecture enables stable transimpedance gain with >1 GΩ feedback resistors without significant offset error accumulation. The non-standard SOIC-8 pinout physically separates IN+/IN− from V+/V− using N/C guard pins, reducing layout-dependent parasitic currents that degrade effective input impedance.

Key Specifications

Pinout & Package

Package: 8-pin SOIC (4.90 mm × 3.90 mm), with non-standard pinout optimized for guarding high-impedance inputs. Two No Connect (N/C) pins serve as guard traces between input and supply terminals.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar precision amplifier applications.

Compared with ADA4530-1ARZ and LTC6268IMS8#PBF, the LMP7721MAX/NOPB uniquely combines guaranteed ±20 fA max bias, SOIC-8 guard-pin layout, and 17 MHz GBW at 1.3 mA - making it optimal for space-constrained, battery-operated electrometer designs where layout-driven leakage dominates error budgets.

Availability

LMP7721MAX/NOPB is available at Aetrix Electronics and suitable for photodiode amplifiers, ion chamber interfaces, and pH meter front-ends requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LMP7721MAX/NOPB 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

Texas Instruments is a global semiconductor leader delivering analog and embedded processing solutions, with over 90,000 products serving industrial, automotive, and personal electronics markets.

The LMP7721MAX/NOPB belongs to TI's LMP™ precision amplifier family, engineered specifically for ultra-high-impedance sensor interfacing where femtoampere-level input bias current and layout-immune guarding are critical to measurement fidelity.

FAQ

What is the maximum guaranteed input bias current for LMP7721MAX/NOPB at 85°C?

The LMP7721MAX/NOPB has a maximum guaranteed input bias current of ±900 fA at 85°C, as specified in the Electrical Characteristics tables for both 2.5 V and 5 V supply conditions. This limit applies when VCM = 1 V and reflects worst-case process and temperature variation across production lots. At 125°C, the limit increases to ±5 pA, maintaining usability in extended-temperature industrial environments. The LMP7721MAX/NOPB achieves this via patented cancellation circuitry that actively compensates for junction leakage.

Does LMP7721MAX/NOPB support true rail-to-rail input common-mode range?

No, the LMP7721MAX/NOPB does not support rail-to-rail input common-mode range. Its input common-mode voltage range is specified as −0.3 V to 4.0 V at 5 V supply (CMRR ≥80 dB), meaning it operates down to 300 mV below V− but only up to 1.0 V below V+. However, it does include the negative rail - enabling ground-sensing in single-supply configurations. This asymmetric range is intentional to optimize input stage linearity and bias current stability, and is clearly documented in Section 6.5 and 6.6 of the LMP7721MAX/NOPB datasheet.

Can LMP7721MAX/NOPB be used with feedback resistors greater than 1 GΩ?

Yes, the LMP7721MAX/NOPB is explicitly designed for use with feedback resistors ≥1 GΩ, enabled by its ±20 fA max input bias current and patented cancellation architecture. At 1 GΩ, this bias contributes only 20 mV of offset error - far lower than alternatives. Successful implementation requires strict adherence to the guard-trace layout guidelines in Section 10, including tying N/C pins 2 and 5 to the same guard potential as the input traces. Layout-induced leakage remains the dominant error source above 100 MΩ, not the LMP7721MAX/NOPB's intrinsic bias.

What is the purpose of the N/C pins on LMP7721MAX/NOPB?

The two N/C pins (pins 2 and 5) on the LMP7721MAX/NOPB are intentionally unconnected internally and serve as physical guards between IN+ and V− (pin 2), and between IN− and V+ (pin 5). Per TI's layout recommendations, these pins should be tied to a dedicated guard trace routed beneath the input nodes - creating a low-impedance equipotential barrier that shunts PCB surface leakage away from the sensitive inputs. This architecture reduces effective input bias current by suppressing contamination- and humidity-induced surface conduction paths, a critical feature confirmed in the "Unique Pinout" section (7.3.6) of the LMP7721MAX/NOPB datasheet.

How does LMP7721MAX/NOPB achieve low input bias current across temperature?

The LMP7721MAX/NOPB achieves stable femtoampere-level input bias across temperature through a patented input bias current cancellation circuit that actively nulls junction leakage components in real time. Unlike conventional JFET or CMOS op-amps whose bias current doubles every ~10°C, the LMP7721MAX/NOPB's cancellation loop tracks and subtracts thermally induced leakage - resulting in only ±900 fA max at 85°C and ±5 pA at 125°C. This behavior is validated across production lots and is not dependent on external trimming. The LMP7721MAX/NOPB's specification sheet confirms this performance in Tables 6.5 and 6.6 under "IBIAS" with explicit temperature-conditioned limits.