Texas Instruments ISO121G

Overview

ISO121G from Burr-Brown is a precision isolation amplifier using duty-cycle modulation across a 2pF differential capacitive barrier, delivering 3500Vrms isolation, ±0.01% max nonlinearity, and 6kHz bandwidth with external 1000pF capacitors - deployed in industrial transducer isolation, 4–20mA loop systems, and biomedical signal conditioning where high common-mode rejection and ground-loop elimination are critical.

For engineers reviewing the ISO121G datasheet, ISO121G pinout, ISO121G application, or ISO121G equivalent, key selection considerations include its 40-pin hermetic DIP package, 3500Vrms rated isolation, IMR of 115dB at 60Hz, user-controllable carrier frequency via Ext Osc input, and bipolar ±10V output swing - all verified for operation from –25°C to +85°C.

Technical Context

The ISO121G implements a laser-trimmed, duty-cycle modulated architecture with matched 1pF barrier capacitors, enabling digital transmission of analog signals while preserving linearity and temperature stability. Its input section integrates VIN/200kΩ against a switched ±100µA current source, generating a triangular waveform whose duty cycle encodes the input voltage.

The output stage demodulates the barrier-crossing signal using synchronized sampling and hold amplifiers to suppress ripple; external capacitors C1 and C2 (e.g., 1000pF each) set bandwidth and stabilize carrier synchronization - with C2 ≥ 0.8×C1 required for stability and 6kHz bandwidth confirmed at C1 = C2 = 1000pF.

Key Specifications

Pinout & Package

ISO121G uses a 40-pin hermetic dual-in-line package (DIP), designated Package Number 206 per Burr-Brown documentation. The package provides galvanic isolation between primary (input) and secondary (output) sides, with separate ground, supply, and signal commons on each side.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ISO121BG, ISO121G offers identical isolation and precision but with standard-grade screening; versus AMC1301DWVR, ISO121G provides analog configurability and ±10V output at the cost of lower bandwidth and discrete capacitor tuning - making it optimal for retrofitting legacy industrial analog systems.

Availability

ISO121G is available at Aetrix Electronics and suitable for industrial process control, motor control feedback, biomedical instrumentation, and power monitoring requiring stable component supply across extended product lifecycles.

Supply support for ISO121G 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

Burr-Brown Corporation was a U.S.-based analog semiconductor pioneer, acquired by Texas Instruments in 2000, renowned for high-precision isolation, data conversion, and signal conditioning ICs.

The ISO121G belongs to Burr-Brown's precision isolation amplifier product line, designed specifically for high-reliability analog signal transfer across hazardous voltage boundaries in industrial, medical, and energy infrastructure applications.

FAQ

What is the isolation voltage rating of the ISO121G and how is it verified?

The ISO121G is rated for 3500Vrms continuous isolation voltage at 60Hz, with 100% production testing at 5600Vrms for 1 second with ≤5pC partial discharge. This verification ensures the integrity of the hermetic ceramic barrier and confirms suitability for use in safety-critical applications such as industrial motor drives and medical isolation barriers where sustained high-voltage withstand is mandatory. The ISO121G maintains this rating across its full specified temperature range.

Can the ISO121G operate with different external capacitor values to adjust bandwidth?

Yes - the ISO121G bandwidth is directly controlled by external capacitors C1 and C2. With C1 = C2 = 0, bandwidth reaches 60kHz; with C1 = C2 = 1000pF, bandwidth reduces to 6kHz while guaranteeing ±0.01% nonlinearity and ±150µV/°C VOS drift. C2 must be ≥0.8×C1 for stability, and values up to 0.022µF are supported for ultra-low-noise, low-bandwidth applications like precision thermocouple conditioning. The ISO121G datasheet provides exact capacitor tables for synchronization and bandwidth targeting.

Does the ISO121G require external components for basic operation?

No - the ISO121G operates with no external components for 60kHz bandwidth operation. For precision specifications (±0.01% nonlinearity, ±150µV/°C drift), two external 1000pF capacitors (C1 and C2) are required. Additional components like 1µF tantalum bypass capacitors on each supply rail are strongly recommended for noise immunity, and guarding traces for C1H/C2H pins is essential to maintain 115dB IMR. The ISO121G does not require external gain-setting resistors or offset trims to meet datasheet performance.

What is the function of the Ext Osc pin on the ISO121G and what signal types are compatible?

The Ext Osc pin on the ISO121G enables external synchronization of the internal carrier frequency to eliminate beat frequencies and reject periodic noise. It accepts ±3V to ±20V square waves (400–700kHz, 25–75% duty cycle), ±4V sine or triangle waves, or conditioned TTL-level signals using the Figure 2 signal conditioner circuit. Synchronization allows precise placement of nulls in the signal response curve - for example, aligning carrier harmonics with 60Hz line noise or DC/DC converter switching frequencies - a capability unique to the ISO121G among precision isolation amplifiers of its era.

How does the ISO121G handle overload recovery and settling time?

The ISO121G exhibits 150µs overload recovery time for 50% output overload with C1 = C2 = 0, and 350µs settling time to 0.01% for VO = ±10V with C1 = C2 = 1000pF. These values are measured under standard conditions (TA = +25°C, VS1 = VS2 = ±15V, RL = 2kΩ) and reflect the combined effect of the modulator/demodulator loop dynamics and internal sample-and-hold filtering. The ISO121G's recovery behavior is deterministic and repeatable - critical for closed-loop control systems where transient response directly impacts stability margins.