Analog Devices Inc./Maxim Integrated MAX843ISA+T

Overview

MAX843ISA+T from Maxim Integrated is a low-noise, inverting charge-pump DC-DC converter optimized for GaAsFET biasing in cellular transmitter amplifiers. It delivers a regulated -2V output at 4mA with 1mV_p-p ripple, operates from 2.5V to 10V input, and features active-low TTL shutdown with <1µA quiescent current over temperature.

For engineers reviewing the MAX843ISA+T datasheet, MAX843ISA+T pinout, MAX843ISA+T application, or MAX843ISA+T equivalent, this device serves as a precision negative bias supply where low noise, small capacitor support (down to 0.22µF), and stable -2V regulation under varying input conditions are critical design requirements.

Technical Context

The MAX843ISA+T implements a two-stage architecture: a capacitive charge pump inverts the input voltage to generate an unregulated negative rail at NEGOUT, followed by an internal low-noise linear regulator that filters and stabilizes the output at OUT. Regulation is controlled via an external positive control voltage (V_CTRL) applied to the CONT pin, enabling precise output setting across -0.5V to -9.4V.

It operates at 100kHz during normal operation and reduces switching frequency to 20kHz in shutdown mode-maintaining active NEGOUT for LCD bias while minimizing power consumption. The device requires no inductors and supports ceramic or tantalum capacitors with ESR <0.8Ω for C1–C3 and <0.2Ω for C4.

Key Specifications

Pinout & Package

MAX843ISA+T is housed in an 8-pin SO package (0.150" wide) with exposed pad not present. Pin functions are validated per Maxim's official datasheet (Rev 1, 3/96) and confirmed on the MAX843-specific top-view diagram.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX840ISA+T and MAX844ISA+T, the MAX843ISA+T uniquely combines CONT-based programmability with full shutdown of both OUT and NEGOUT-making it optimal for RF bias applications requiring complete power gating without auxiliary rail leakage.

Availability

MAX843ISA+T is available at Aetrix Electronics and suitable for cellular phone transmitter amplifiers, GaAsFET power amplifier modules, and personal communicator designs requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for MAX843ISA+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) is a semiconductor company specializing in high-performance analog, mixed-signal, and power management ICs for industrial, communications, and consumer applications.

The MAX843ISA+T belongs to Maxim's GaAsFET bias power supply product line, engineered specifically for low-noise, inductorless negative voltage generation in RF front-end circuits of portable wireless transmitters.

FAQ

What is the primary function of the MAX843ISA+T?

The MAX843ISA+T is a low-noise, inverting charge-pump DC-DC converter designed to generate a regulated negative output voltage-typically −2V-for biasing GaAsFET gate terminals in RF power amplifier stages. Its architecture combines a capacitive charge pump with an internal linear regulator to achieve 1mV_p-p output ripple, making the MAX843ISA+T ideal for noise-sensitive RF applications where inductor-based solutions are impractical.

How does the MAX843ISA+T set its output voltage?

The MAX843ISA+T sets its output voltage using an external positive control voltage (V_CTRL) applied to the CONT pin. A resistor divider between OUT and V_CTRL determines the final output: V_OUT = −V_CTRL × (R2/R1). This allows precise, externally adjustable regulation from −0.5V to −9.4V at up to 4mA-unlike the MAX840ISA+T, which uses FB pin feedback. The MAX843ISA+T does not support fixed −2V operation without external components.

What happens to the outputs of the MAX843ISA+T during shutdown?

When the SHDN pin is pulled low, the MAX843ISA+T disables both the linear regulator and the charge-pump oscillator-fully deactivating OUT and NEGOUT. This differs from the MAX844ISA+T, where NEGOUT remains active in shutdown. The MAX843ISA+T's complete output disablement ensures zero load current draw from either rail, supporting true power-gating requirements in battery-powered RF transmitters.

Can the MAX843ISA+T operate with small capacitors?

Yes-the MAX843ISA+T is explicitly characterized to operate with flying capacitors as small as 0.22µF (C1, C2, C3) and output capacitor C4 = 4.7µF. Using these values increases output ripple slightly (still ≤1mV_p-p with proper layout), but significantly reduces PCB area and cost versus 1µF/10µF configurations. Ceramic or low-ESR tantalum capacitors are required; ESR must be <0.8Ω for C1–C3 and <0.2Ω for C4 to maintain regulation integrity in the MAX843ISA+T.

What is the operating temperature range of the MAX843ISA+T?

The MAX843ISA+T is specified for operation from −25°C to +85°C, as indicated by the "ISA" suffix in its ordering code. This industrial-grade temperature range ensures reliable performance in handheld wireless devices exposed to ambient thermal variations-from cold outdoor environments to warm enclosed enclosures. The device maintains its key specifications-including 1mV_p-p ripple and <1µA shutdown current-across this full range, as verified in Maxim's Electrical Characteristics table.