Analog Devices Inc./Maxim Integrated MAX850ISA+T

Overview

MAX850ISA+T from Maxim Integrated is a low-noise, inverting, regulated charge-pump DC/DC converter designed to generate a stable -4.1V output for GaAsFET gate bias in cellular transmitter amplifiers. It operates from 4.5V to 10V input, delivers up to 5mA output current, features 2mV_p-p output ripple, and includes logic-level shutdown with <1µA max quiescent current over temperature.

For engineers reviewing the MAX850ISA+T datasheet, MAX850ISA+T pinout, MAX850ISA+T application, or MAX850ISA+T equivalent, this device is selected for precision negative biasing where ultra-low noise, fixed-output regulation, and minimal PCB footprint in an 8-pin SO package are critical - especially in RF power amplifier stages requiring stable V_GG.

Technical Context

The MAX850ISA+T integrates a capacitive charge pump followed by an internal N-channel linear regulator to invert and tightly regulate VIN into a clean negative output. Its feedback pin (FB) is internally referenced to -1.28V, enabling fixed -4.1V output when grounded or adjustable output via external resistor divider.

It uses a 100kHz internal oscillator (non-synchronizable), supports TTL-compatible active-low shutdown on Pin 4, and achieves <2mV_p-p ripple through post-regulation filtering - distinct from the MAX852 (external clock) and MAX853 (voltage-controlled output).

Key Specifications

Pinout & Package

MAX850ISA+T is housed in an 8-pin plastic Small-Outline (SO) package, 150mil wide, with standard JEDEC MS-012AC dimensions (5.0mm × 4.0mm × 1.75mm height). Pin 1 is marked by a beveled corner or dot.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX851ISA+T and LM2776IDR, the MAX850ISA+T uniquely balances fixed -4.1V accuracy, ultra-low shutdown current, and wide 4.5V–10V input range - making it optimal for primary-battery-powered cellular transmitters where bias stability and battery longevity are jointly critical.

Availability

MAX850ISA+T is available at Aetrix Electronics and suitable for cellular phone RF modules, wireless data loggers, personal communicators, and LCD contrast control circuits requiring stable component supply, long-term lifecycle support, and guaranteed traceable sourcing.

Supply support for MAX850ISA+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 MAX850–MAX853 family was engineered specifically for low-noise, compact GaAsFET bias generation in portable RF transmitters - prioritizing ripple suppression, shutdown efficiency, and ease of integration over general-purpose DC/DC flexibility.

FAQ

What is the output voltage tolerance of the MAX850ISA+T under full load?

The MAX850ISA+T delivers -4.1V ±0.1V at 5mA load and 4.5V–10V input, per its Electrical Characteristics table. This tight tolerance ensures consistent GaAsFET gate bias across operating conditions, minimizing gain drift in RF power amplifiers. The internal -1.28V reference and feedback architecture maintain this accuracy without external trimming. MAX850ISA+T achieves this specification across its full -25°C to +85°C operating range.

Can the MAX850ISA+T be used with a 3.3V input supply?

No - the MAX850ISA+T requires a minimum 4.5V input to sustain -4.1V output regulation. At inputs below 4.5V, the internal charge pump cannot generate sufficient headroom for the linear regulator stage, causing output collapse or unregulated behavior. For 3.3V systems, consider alternatives like the MAX860 or TI's LM2776, which support lower VIN. MAX850ISA+T is strictly specified for 4.5V–10V operation.

How does the MAX850ISA+T achieve 2mV_p-p output ripple?

The MAX850ISA+T combines a 100kHz charge-pump inverter with a post-regulating N-channel linear stage that filters switching artifacts. Unlike basic charge pumps, its integrated LDO rejects both pump ripple and supply noise - reducing residual AC content to 2mV_p-p at the OUT pin. This is verified under standard test conditions (VIN=6V, IOUT=5mA, AC-coupled measurement across C4). MAX850ISA+T relies on this dual-stage architecture, not external LC filtering, to meet its ripple spec.

Is the MAX850ISA+T pin-compatible with the MAX852ISA+T?

No - although both are 8-pin SO devices, MAX850ISA+T and MAX852ISA+T have different pin functions: Pin 4 is SHDN (active-low) on MAX850ISA+T but OSC (external clock input) on MAX852ISA+T, and Pin 5 is FB on MAX850ISA+T but unused on MAX852ISA+T. Swapping them without PCB revision will cause functional failure. MAX850ISA+T is not a drop-in replacement for MAX852ISA+T or any other member of the MAX85x family beyond MAX851ISA+T.

What external capacitors are required for stable operation of the MAX850ISA+T?

The MAX850ISA+T requires four external capacitors: two 1µF low-ESR (≤0.8Ω) flying capacitors (C1+, C1−), one 1µF input bypass capacitor (C3), and one 10µF low-ESR (≤0.2Ω) output filter capacitor (C4). Ceramic or chip tantalum types are recommended. These values are validated in the Typical Operating Circuit (Figure 2a) and ensure stable regulation, low dropout, and minimal ripple. Deviating from these degrades MAX850ISA+T performance - especially C4, which directly sets measured ripple.