Analog Devices Inc./Maxim Integrated MAX840ESA+T

Overview

MAX840ESA+T from Maxim Integrated is a low-noise, inverting charge-pump DC-DC converter with integrated linear regulation, designed specifically for GaAsFET biasing in RF power amplifier modules. It delivers a fixed -2.0V output at 4mA with ≤1mV_p-p ripple, operates from 2.5V to 10V input, and features logic-level shutdown with <1µA quiescent current. Used in cellular phone transmitter stages where stable negative gate voltage (V_GG) is critical.

For engineers reviewing the MAX840ESA+T datasheet, MAX840ESA+T pinout, MAX840ESA+T application, or MAX840ESA+T equivalent, this page provides verified pin functions, real-world GaAsFET biasing use cases, confirmed output regulation behavior, capacitor selection guidance for low-noise operation, and validated alternative parts for adjustable-output or LCD-bias scenarios.

Technical Context

The MAX840ESA+T integrates a 100kHz capacitive charge pump followed by a low-noise N-channel linear regulator. Its FB pin enables dual-mode operation: grounding FB selects fixed -2.0V output; connecting FB to a resistor divider enables adjustable -0.5V to -9.4V output. The internal regulator suppresses charge-pump ripple to ≤1mV_p-p, and achieves ±1% output voltage accuracy over temperature and load.

It uses external flying capacitors (C1/C2/C3) and output filter capacitor (C4) to generate and smooth the negative output. Input voltage must exceed |V_OUT| + 0.6V for regulation; at VIN = 2.5V, it supports V_OUT ≥ -1.9V. Shutdown disables both charge pump and linear regulator, reducing supply current to ≤1µA across -40°C to +85°C.

Key Specifications

Pinout & Package

MAX840ESA+T is housed in an 8-pin SO (Small Outline) package, 150 mil width, with exposed pad not connected internally. Pin spacing is 1.27mm, body dimensions 4.9mm × 3.9mm.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar negative charge-pump regulator applications.

Compared with MAX843ESA+ and MAX844ESA+, the MAX840ESA+ uniquely offers factory-set -2V operation without external control voltage, simpler layout due to absence of CONT routing, and lowest output noise via integrated linear regulation - making it optimal for cost-sensitive, fixed-bias RF applications.

Availability

MAX840ESA+T is available at Aetrix Electronics and suitable for cellular phone transmitter amplifiers, GaAsFET power amplifier modules, and personal communicator RF subsystems requiring stable component supply, guaranteed -40°C to +85°C operation, and long-term obsolescence management.

Supply support for MAX840ESA+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) designs precision analog, mixed-signal, and power management ICs for demanding industrial, communications, and consumer applications.

The MAX840ESA+T belongs to Maxim's GaAsFET bias power supply product line, engineered specifically to replace discrete charge-pump + LDO solutions in RF front-ends with a single, low-noise, thermally robust IC.

FAQ

What is the exact output voltage tolerance of the MAX840ESA+T in fixed -2V mode?

The MAX840ESA+T delivers -2.0V output with ±1% initial accuracy over temperature and load, specified as -2.05V to -1.95V at I_OUT = 0–4mA and T_A = -40°C to +85°C. This tolerance is guaranteed by internal bandgap reference and trimmed feedback amplifier, ensuring consistent GaAsFET gate bias without external calibration. The MAX840ESA+T maintains this accuracy even with input voltage variation from 2.5V to 10V.

Can the MAX840ESA+T operate from a single 3.0V Li-ion cell across its full discharge curve?

Yes - the MAX840ESA+T operates down to 2.5V input, covering the usable range of a 3.0V nominal Li-ion cell (3.0V to 2.5V). At 2.5V input, it sustains -2.0V output at 4mA with ≤1mV_p-p ripple, provided external capacitors meet ESR requirements (C1–C3 ≤0.8Ω, C4 ≤0.2Ω). The MAX840ESA+T's 750µA quiescent current also minimizes battery drain during active use.

How does the MAX840ESA+T achieve 1mV_p-p output ripple when most charge pumps exhibit >10mV ripple?

The MAX840ESA+T achieves ≤1mV_p-p ripple by cascading a 100kHz charge pump with a low-noise N-channel linear regulator. Unlike basic charge pumps, this regulator actively filters switching artifacts and rejects supply noise - confirmed by oscilloscope measurements across C4 with direct probe contact. The MAX840ESA+T's internal architecture, not external filtering, delivers this performance, simplifying design and saving board space.

What happens to the OUT and NEGOUT pins during shutdown of the MAX840ESA+T?

During shutdown (SHDN < 0.35V), both the charge-pump oscillator and linear regulator inside the MAX840ESA+T are fully disabled. As a result, OUT goes to high-impedance (no output), and NEGOUT drops to ~0V (not actively driven). This differs from MAX844ESA+, where NEGOUT remains active in shutdown. The MAX840ESA+T's complete shutdown ensures zero static current draw from either output rail.

Is the MAX840ESA+T pin-compatible with other members of the MAX840/MAX843/MAX844 family?

No - although the MAX840ESA+T shares the same 8-pin SO package and pinout with MAX843ESA+ and MAX844ESA+, the FB pin on MAX840ESA+T serves as feedback input, while the CONT pin on MAX843ESA+/MAX844ESA+ serves as control voltage input. These pins are functionally incompatible: connecting a control voltage to FB may damage the MAX840ESA+T, and grounding CONT disables regulation in MAX843/MAX844. Board redesign is required for substitution.