Analog Devices Inc./Maxim Integrated MAX840ISA+

Overview

MAX840ISA+ 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 stages. 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 modules where stable negative gate voltage (V_GG) is critical.

For engineers reviewing the MAX840ISA+ datasheet, MAX840ISA+ pinout, MAX840ISA+ application, or MAX840ISA+ equivalent, key selection criteria include regulated negative output stability under load variation, ultra-low noise performance in RF-sensitive bias rails, shutdown current budgeting, capacitor size constraints (down to 0.22µF), and SO-8 package compatibility with GaAsFET amplifier layouts.

Technical Context

The MAX840ISA+ integrates a 100kHz charge-pump inverter followed by an N-channel linear regulator to suppress switching ripple. Its feedback pin (FB) enables either fixed -2V operation (when grounded) or adjustable -0.5V to -9.4V output via external resistor divider - though only the fixed mode is characterized for this variant. The internal regulator's AC rejection attenuates supply noise, making it suitable for sensitive RF bias nodes.

During shutdown, both charge-pump oscillator and linear regulator disable completely, reducing supply current to ≤1µA over temperature. Unlike MAX844, the MAX840ISA+ does not maintain NEGOUT in shutdown - all outputs are inactive. Its SO-8 package places C1+/C1−, IN, GND, OUT, FB, SHDN, and NEGOUT on standard 1.27mm pitch leads for compact RF layout.

Key Specifications

Pinout & Package

MAX840ISA+ uses an 8-pin SO package (150mil width, 1.27mm lead pitch) with exposed pad not connected internally. Pin functions are validated per Maxim's official datasheet Rev 1 (19-0388) and top-view schematic.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX840ESA+, the MAX840ISA+ trades extended temperature capability for lower cost and same core performance in commercial environments; compared with MAX843ISA+, it offers simpler fixed-output implementation without external control voltage circuitry, reducing design complexity and component count for dedicated -2V bias rails.

Availability

MAX840ISA+ is available at Aetrix Electronics and suitable for cellular phone transmitter amplifiers, GaAsFET power amplifier modules, and regulated negative power supplies requiring stable component supply, full traceability, and long-term lifecycle support.

Supply support for MAX840ISA+ 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) is a semiconductor company specializing in high-performance analog, mixed-signal, and power-management ICs for industrial, communications, and consumer applications.

The MAX840ISA+ belongs to Maxim's GaAsFET bias power-supply product line, engineered specifically to deliver ultra-low-noise, regulated negative voltages for RF power amplifier gate control in battery-powered wireless devices.

FAQ

What is the guaranteed output voltage accuracy of the MAX840ISA+?

The MAX840ISA+ guarantees an output voltage of -2.0V ±50mV (i.e., -1.95V to -2.05V) across its full operating temperature range (-25°C to +85°C), load (0–4mA), and input voltage (2.5V–10V). This specification is verified per Maxim's datasheet Rev 1, ensuring reliable GaAsFET gate biasing without drift-induced gain compression. The MAX840ISA+ achieves this using an internal bandgap-referenced linear regulator with tight feedback tolerance.

Can the MAX840ISA+ operate from a single 3.6V Li-ion cell?

Yes, the MAX840ISA+ operates from 2.5V to 10V input, making it fully compatible with a single 3.6V nominal Li-ion cell across its discharge curve (3.0V–4.2V). At 3.6V input, it delivers -2.0V at 4mA with ≤1mV_p-p ripple and 750µA supply current. The 2.5V minimum ensures functionality even at end-of-discharge, critical for maintaining PA linearity in cellular handsets using the MAX840ISA+.

Does the MAX840ISA+ require external components to function?

Yes, the MAX840ISA+ requires four external capacitors: C1 and C2 (flying caps, 0.22µF–1µF), C3 (input bypass, 0.1µF), and C4 (output filter, 4.7µF–10µF). These are mandatory for charge-pump operation and ripple suppression. No resistors are needed for fixed -2V mode (FB grounded), but a resistor divider is required if using adjustable output. All capacitors must be low-ESR ceramic or tantalum types per Maxim's layout guidelines.

How does shutdown mode affect the outputs of the MAX840ISA+?

In shutdown mode (SHDN ≤0.35V), the MAX840ISA+ disables both the 100kHz charge-pump oscillator and the internal linear regulator. As a result, OUT and NEGOUT drop to high-impedance states with no output current capability. Supply current falls to ≤1µA over temperature. This behavior differs from MAX844, which maintains NEGOUT in shutdown - confirming the MAX840ISA+ is optimized for complete power gating in GaAsFET bias applications.

Is the MAX840ISA+ pin-compatible with other variants in the MAX840 family?

Yes, the MAX840ISA+ shares identical pinout and package (8-pin SO) with MAX840ESA+, MAX840C/D, and all MAX843/MAX844 variants. Pin functions - including C1+, C1−, NEGOUT, SHDN, FB/CONT, OUT, GND, and IN - match exactly across the family. However, FB and CONT pins serve different functions: MAX840ISA+ uses FB for fixed/adjustable output, while MAX843ISA+ uses CONT for voltage-controlled output, so interchanging them requires circuit modification.