Analog Devices Inc. LT1931AIS5#TRMPBF

Overview

LT1931AIS5#TRMPBF from Analog Devices (formerly Linear Technology) is a 2.2MHz fixed-frequency inverting current-mode DC/DC converter in a 5-lead ThinSOT package, integrating a 1A switch to deliver –5V at 300mA from a 5V input or –12V at 150mA from 5V. It features 1mV_P-P output ripple, 400mV V_CE(SAT) at 1A, and operates across 2.6V–16V input range for compact negative bias generation in space-constrained analog systems.

For engineers reviewing the LT1931AIS5#TRMPBF datasheet, LT1931AIS5#TRMPBF pinout, LT1931AIS5#TRMPBF application, or LT1931AIS5#TRMPBF equivalent, this page delivers verified electrical specs, validated pin functions, confirmed dual-inductor inverting topology behavior, and real-world design trade-offs between LT1931A and LT1931 variants - all critical for low-noise negative supply selection in CCD, LCD, and GaAs FET bias circuits.

Technical Context

The LT1931AIS5#TRMPBF employs constant-frequency current-mode control with a 2.2MHz oscillator, enabling ceramic capacitor use and minimizing solution height to ≤2mm. Its dual inductor inverting topology filters both input and output currents, achieving <1mV_P-P ripple with X5R ceramics and maintaining output regulation within ±1% during load transients.

It integrates a 36V-rated switch with 400mV typical V_CE(SAT) at 1A and supports up to 75% duty cycle, limiting usable V_IN/|V_OUT| ratios to ≤3.7 (e.g., 5V→–16V exceeds limit). Feedback is referenced to –1.255V at NFB pin, with 8µA typical bias current flowing out of the pin for resistive divider design.

Key Specifications

Pinout & Package

LT1931AIS5#TRMPBF is housed in a 5-lead ThinSOT (TSOT-23) package, 2.9mm × 1.6mm × 1.0mm profile, with exposed pad not connected internally. Pin 1 (SW) carries high di/dt switching current; Pin 2 (GND) must tie directly to local ground plane; Pin 3 (NFB) sources bias current and requires short, low-capacitance trace; Pin 4 (SHDN) is active-high enable; Pin 5 (VIN) requires local 1µF ceramic bypass.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar inverting DC/DC converter applications.

Compared with LT1931IS5#TRMPBF, the LT1931AIS5#TRMPBF trades 5–8% efficiency and ~50mA output current for 40% smaller magnetics and thinner solution height; versus LT1611ES5#TRMPBF, it delivers 2× output current in same footprint with integrated switch and superior noise performance.

Availability

LT1931AIS5#TRMPBF is available at Aetrix Electronics and suitable for disk drive MR head bias, digital camera CCD bias, LCD panel bias, and GaAs FET RF amplifier bias applications requiring stable component supply, consistent parametric performance, and long-term industrial availability.

Supply support for LT1931AIS5#TRMPBF 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

Analog Devices acquired Linear Technology in 2017 and maintains full product support, manufacturing, and documentation for legacy Linear parts including the LT1931A series.

The LT1931A product line was designed specifically for high-power-density, low-noise negative voltage generation in analog-intensive systems such as imaging sensors, RF front-ends, and precision data acquisition - prioritizing ripple suppression, thermal efficiency, and minimal external component count.

FAQ

What is the maximum achievable output current for LT1931AIS5#TRMPBF at –5V from a 5V input?

The LT1931AIS5#TRMPBF delivers up to 300mA at –5V from a 5V input under typical conditions (T_A = 25°C, proper layout, 4.7µH coupled inductors). This limit arises from its 75% maximum duty cycle and thermal constraints in the ThinSOT package. At higher ambient temperatures or with poor PCB copper area, derating to 250mA is recommended to maintain reliability and regulation accuracy.

Can LT1931AIS5#TRMPBF generate –12V from a 5V input?

Yes, the LT1931AIS5#TRMPBF can generate –12V from 5V input, delivering up to 150mA. The required duty cycle is 70.6%, which falls within its 75% maximum limit. However, efficiency drops ~5% compared to –5V operation due to higher conduction losses and reduced switch utilization. Use ceramic output capacitors ≥10µF and ensure adequate thermal relief on GND pad.

How does the NFB pin bias current affect output voltage accuracy in LT1931AIS5#TRMPBF designs?

The NFB pin of LT1931AIS5#TRMPBF sources 8µA typical bias current, meaning current flows *out* of the pin into the feedback divider. If unaccounted for, this introduces a systematic error: for a –5V output using R1=28.7kΩ and R2=10kΩ, the actual output deviates by ~1.2%. To correct, increase R1 value per the formula |V_OUT| = 1.255 × (1 + R1/R2) + (1.255 × I_NFB × R1), ensuring ±1.5% total accuracy.

What is the purpose of the phase-lead capacitor (C4) between NFB and VOUT in LT1931AIS5#TRMPBF applications?

The phase-lead capacitor C4 (e.g., 220pF) placed across R1 in the LT1931AIS5#TRMPBF feedback network introduces a zero in the control loop transfer function, improving phase margin and damping output voltage overshoot during load transients. Without C4, the converter exhibits ringing (Figure 3); with C4, response becomes critically damped (Figure 4). Target zero frequency is 20–60kHz - set via f_Z = 1/(2π × R1 × C4).

Is LT1931AIS5#TRMPBF pin-compatible with LT1611ES5#TRMPBF?

Yes, LT1931AIS5#TRMPBF is pin-for-pin compatible with LT1611ES5#TRMPBF per Linear Technology documentation, sharing identical 5-lead ThinSOT pinout (SW, GND, NFB, SHDN, VIN). However, LT1931AIS5#TRMPBF integrates a 1A switch and supports higher output current (300mA vs. 150mA), requiring review of inductor and diode ratings in existing LT1611 layouts before drop-in replacement.