Analog Devices Inc./Maxim Integrated MAX843ISA+

Overview

MAX843ISA+ from Maxim Integrated is a low-noise, inverting charge-pump DC-DC converter optimized for GaAsFET biasing in cellular transmitter power amplifiers. It delivers a regulated -2V output at 4mA with ≤1mV_p-p ripple, operates from 2.5V to 10V input, and uses an external control voltage (V_CTRL) to set output voltage across -0.5V to -9.4V range.

For engineers reviewing the MAX843ISA+ datasheet, MAX843ISA+ pinout, MAX843ISA+ application, or MAX843ISA+ equivalent, key selection criteria include its adjustable negative output via V_CTRL, 100kHz switching frequency in normal mode, 20kHz in shutdown (MAX844 only), SO-8 package compatibility, and GaAsFET bias-specific regulation performance under low-input-voltage conditions.

Technical Context

The MAX843ISA+ implements a two-stage architecture: a capacitive charge pump inverts VIN to generate unregulated NEGOUT, followed by a low-noise linear regulator that produces the stable, ripple-filtered OUT. Regulation is achieved via external resistor divider feedback from OUT to CONT pin, enabling precise output voltage setting independent of input variation.

Its shutdown logic disables both charge pump oscillator and linear regulator, reducing supply current to ≤1µA over temperature. Unlike the MAX844, the MAX843ISA+ fully disables NEGOUT and OUT in shutdown - no residual output remains active, eliminating unintended LCD bias leakage during sleep modes.

Key Specifications

Pinout & Package

MAX843ISA+ is housed in an 8-pin SO (Small Outline) package with standard 1.27mm lead pitch and JEDEC MS-012AC outline. Thermal pad not present; power dissipation limited to 471mW at +70°C ambient.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar negative-bias power supply applications.

Compared with MAX840ISA+, the MAX843ISA+ adds V_CTRL-based adjustability at identical quiescent current and ripple performance; compared with LM27761DSGR, it offers superior noise performance and smaller BOM for GaAsFET bias but lacks multi-rail flexibility and higher current delivery.

Availability

MAX843ISA+ is available at Aetrix Electronics and suitable for cellular phone transmitter amplifiers, GaAsFET power amplifier modules, and wireless data loggers requiring stable component supply with guaranteed long-term availability and traceable sourcing.

Supply support for MAX843ISA+ 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 MAX843ISA+ belongs to Maxim's GaAsFET bias power supply product line, engineered specifically to deliver ultra-low-noise, tightly regulated negative voltages for RF power amplifier gate control in battery-powered wireless infrastructure and handsets.

FAQ

What is the function of the CONT pin on the MAX843ISA+?

The CONT pin on the MAX843ISA+ serves as the voltage-controlled feedback input. It accepts an external positive control voltage (V_CTRL) between 0V and 10V, enabling precise setting of the regulated negative output voltage using the formula V_OUT = –V_CTRL × (R2/R1). This allows dynamic adjustment of GaAsFET gate bias without modifying hardware, making the MAX843ISA+ ideal for adaptive RF power control schemes.

Does the MAX843ISA+ remain functional at 2.5V input voltage?

Yes, the MAX843ISA+ operates fully functional down to 2.5V input voltage, delivering up to 4mA output current with ≤1mV_p-p ripple when VIN > 2.7V. At exactly 2.5V, output current capability reduces slightly but remains sufficient for most GaAsFET bias applications. This low-VIN operation ensures reliable performance throughout the discharge curve of single-cell Li-ion batteries, a key requirement for the MAX843ISA+ in portable RF transmitters.

How does shutdown behavior differ between MAX843ISA+ and MAX844ISA+?

In shutdown mode, the MAX843ISA+ disables both the charge-pump oscillator and the linear regulator, turning off OUT and NEGOUT completely with ≤1µA supply current. In contrast, the MAX844ISA+ keeps NEGOUT active (at reduced 20kHz switching) to support LCD bias while disabling only the linear regulator. This fundamental difference means the MAX843ISA+ is preferred when zero leakage during sleep is mandatory, whereas MAX844ISA+ targets dual-role applications requiring persistent negative rail generation.

Can the MAX843ISA+ use 0.22µF capacitors instead of 1µF?

Yes, the MAX843ISA+ supports 0.22µF flying capacitors (C1, C2, C3) and a 4.7µF output capacitor (C4), as confirmed in Maxim's typical operating circuits. Using these smaller values increases output ripple to ~1mV_p-p (still within spec) and slightly raises noise floor, but significantly reduces BOM cost and PCB area. This trade-off is validated for GaAsFET bias applications and is explicitly supported in the MAX843ISA+ datasheet, making it a viable option for space-constrained designs.

Is the MAX843ISA+ pin-compatible with the MAX840ISA+?

No, the MAX843ISA+ is not pin-compatible with the MAX840ISA+. While both use the same 8-pin SO package, their pin functions differ: MAX840ISA+ uses Pin 5 as FB (feedback), whereas MAX843ISA+ uses Pin 5 as CONT (control voltage input). Pins 1–4 and 6–8 share identical roles, but the FB/CONT swap prevents direct replacement without PCB modification. This distinction is critical when selecting between fixed-bias (MAX840ISA+) and voltage-programmable (MAX843ISA+) variants.