Analog Devices Inc. LTC1261LIS8-4#TRPBF

Overview

LTC1261LIS8-4#TRPBF from Analog Devices (formerly Linear Technology) is a fixed-output switched-capacitor voltage inverter IC that generates a regulated –4V output from a single 4.35V to 5.25V positive supply. It delivers up to 20mA output current with ±4.5% regulation accuracy, features an open-drain REG flag indicating output-in-regulation status, and operates with only three external capacitors. It is used in GaAs FET bias generation and battery-powered negative supply applications.

For engineers reviewing the LTC1261LIS8-4#TRPBF datasheet, LTC1261LIS8-4#TRPBF pinout, LTC1261LIS8-4#TRPBF application, or LTC1261LIS8-4#TRPBF equivalent, key selection criteria include guaranteed –4V output regulation across industrial temperature (–40°C to +85°C), shutdown quiescent current of 5µA, internal 650kHz oscillator, MSOP-8 package compatibility, and REG pin logic behavior referenced to VOUT rather than ground.

Technical Context

The LTC1261LIS8-4#TRPBF implements an inverting charge pump topology with internal 650kHz clock driving S1–S4 MOSFET switches to transfer charge from a 0.1µF flying capacitor to the output. Regulation is achieved via a 1.23V internal reference comparator (COMP1) monitoring a divided replica of VOUT at the ADJ/COMP pin, dynamically truncating clock pulses to maintain output accuracy.

A second comparator (COMP2, 1.17V threshold) drives the open-drain REG output low when the magnitude of VOUT is within 5% of the setpoint (i.e., ≥ –3.8V for –4V output). The device includes internal resistor divider for fixed –4V operation, eliminating external feedback components, and supports optional 100pF compensation capacitor from COMP to GND to stabilize loop bandwidth and reduce ripple.

Key Specifications

Pinout & Package

Package: 8-lead plastic SO (S8), 150°C max junction temperature, θJA = 135°C/W. RoHS-compliant lead-free finish.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar switched-capacitor inverter applications.

Compared with MAX680ESA+ and TPS60403DBVR, the LTC1261LIS8-4#TRPBF offers exact –4V output without trimming, integrated REG signaling referenced to VOUT, and proven industrial-temperature reliability - making it optimal for GaAs bias and instrumentation where output accuracy and power-valid assurance are critical.

Availability

LTC1261LIS8-4#TRPBF is available at Aetrix Electronics and suitable for GaAs FET bias generators, portable instrumentation power supplies, and industrial sensor signal conditioning requiring stable component supply across extended temperature ranges.

Supply support for LTC1261LIS8-4#TRPBF 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 its legacy precision analog portfolio, emphasizing high-performance power management, signal conditioning, and RF solutions for demanding industrial and communications applications.

The LTC1261LIS8-4#TRPBF belongs to Linear's switched-capacitor inverter family, designed specifically to replace inductor-based negative supplies in space-constrained, low-noise, and battery-sensitive systems - prioritizing simplicity, regulation fidelity, and robustness over raw efficiency.

FAQ

What is the minimum input voltage required for stable operation of the LTC1261LIS8-4#TRPBF?

The LTC1261LIS8-4#TRPBF requires a minimum supply voltage of 4.35V to guarantee ±4.5% output regulation at full 20mA load. Operation below this voltage may sustain functionality but violates the specified regulation accuracy per the Electrical Characteristics table. At 4.35V input, the device delivers –4.0V ±4.5% across –40°C to +85°C, confirmed in the "Output Regulation (LTC1261L/LTC1261L-4)" row of the datasheet.

How does the REG pin on the LTC1261LIS8-4#TRPBF behave under varying load conditions?

The REG pin on the LTC1261LIS8-4#TRPBF is an open-drain output that pulls low only when the magnitude of VOUT is within 5% of the nominal –4V setpoint (i.e., ≥ –3.8V). It remains high (high-impedance) when VOUT drops below –3.8V due to overload or input sag. This behavior is independent of load current up to 20mA, as verified in the Electrical Characteristics table under "REG Sink Current" and "VOL" parameters at 5V VCC and –4V VOUT.

Can the LTC1261LIS8-4#TRPBF be used with a 3.3V input supply?

No, the LTC1261LIS8-4#TRPBF cannot be used with a 3.3V input supply. Its absolute minimum VCC is 4.35V, as specified in the Electrical Characteristics table for the -4 variant. Attempting operation at 3.3V will result in failure to regulate - the output collapses toward 0V, and the REG pin remains high. For 3.3V-compatible inverters, consider the adjustable LTC1261L (non–4 version), which supports 2.7V–5.25V inputs.

What is the purpose of the 100pF capacitor recommended between COMP and GND in the LTC1261LIS8-4#TRPBF application circuit?

The 100pF capacitor between COMP and GND in the LTC1261LIS8-4#TRPBF application circuit compensates the internal regulation loop by counteracting parasitic capacitance at the feedback node, thereby increasing loop bandwidth and reducing output voltage ripple. As explained in the Applications Information section, this capacitor stabilizes comparator response to rapid output transients, preventing "hunting" behavior and maintaining tight regulation - especially critical under dynamic load conditions.

Does the LTC1261LIS8-4#TRPBF require special PCB layout considerations for EMI reduction?

Yes, the LTC1261LIS8-4#TRPBF requires careful PCB layout to minimize EMI: place the 0.1µF flying capacitor directly between C1+ and C1– pins with shortest possible traces; locate the 1µF VCC bypass capacitor adjacent to Pin 1; use a solid ground plane beneath the IC; avoid routing sensitive analog traces near the OUT or COMP nodes; and keep the 3.3µF output capacitor close to Pin 6 and GND. These practices mitigate high-frequency charge-pump noise, as emphasized in the "Capacitor Selection" and "Output Ripple" sections of the datasheet.