Analog Devices Inc./Maxim Integrated MAX850ISA+

Overview

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

For engineers reviewing the MAX850ISA+ datasheet, MAX850ISA+ pinout, MAX850ISA+ application, or MAX850ISA+ equivalent, this device is selected for precision negative bias generation where low noise, fixed-output stability, and minimal quiescent current in shutdown are critical - especially in RF front-end power management.

Technical Context

The MAX850ISA+ uses a two-stage architecture: a capacitive charge pump inverts the input voltage to produce an unregulated negative rail at NEGOUT, followed by an internal N-channel linear regulator that stabilizes the final output at OUT. Regulation is achieved via a fixed internal reference (−1.28V) applied to the FB pin, which is grounded to set −4.1V output.

It operates at a fixed 100kHz switching frequency, requires no external clock, and integrates TTL-compatible active-low SHDN control. The SO-8 package supports compact RF layout with dedicated C1+/C1− pins for low-ESR flying capacitor placement and GND/IN separation to minimize noise coupling.

Key Specifications

Pinout & Package

MAX850ISA+ is housed in an 8-pin SO (Small Outline) package, 3.9mm × 4.9mm body size, with standard 1.27mm lead pitch and gull-wing leads. Thermal performance supports 471mW continuous dissipation at +70°C ambient.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX851ISA+, MAX850ISA+ offers simpler control interface for active-low systems; compared with LM2776IDR, it delivers superior noise performance and integrated regulation at the expense of output flexibility and current capability - making it the preferred choice for RF GaAsFET bias where spectral purity is paramount.

Availability

MAX850ISA+ is available at Aetrix Electronics and suitable for cellular handset design, wireless data logger development, and personal communicator RF front-end integration requiring stable component supply, long-term manufacturability, and guaranteed traceability.

Supply support for MAX850ISA+ 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 GaAsFET biasing in portable RF transmitters, prioritizing ripple suppression, shutdown efficiency, and compact integration over programmability or wide output range.

FAQ

What is the output voltage tolerance of the MAX850ISA+?

The MAX850ISA+ provides a fixed −4.1V output with ±2% tolerance over temperature and load. This specification is verified across the full −25°C to +85°C operating range and at output currents from 0mA to 5mA, ensuring reliable GaAsFET gate biasing without external trimming or calibration. The MAX850ISA+ achieves this using an internal −1.28V reference and precision resistor network routed internally to the FB pin.

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

No - the MAX850ISA+ requires a minimum 4.5V input to maintain regulation at −4.1V output. At VIN < 4.5V, the internal linear regulator cannot sustain the required headroom (VIN must exceed |VOUT| + 1.0V), resulting in unregulated or drooping output. For 3.3V systems, consider the MAX863 or MAX881R families, which support lower input ranges. The MAX850ISA+ is strictly specified for 4.5V–10V operation per its Absolute Maximum Ratings and Electrical Characteristics tables.

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

The MAX850ISA+ achieves 2mV_p-p output ripple through cascaded noise reduction: first, the 100kHz charge pump generates a coarse negative rail at NEGOUT; second, an internal N-channel linear regulator filters switching artifacts and supplies rejection. This two-stage architecture - combined with low-ESR external capacitors (1µF C1/C2, 10µF C4) - attenuates high-frequency pump noise and supply-line disturbances. Measurement must be performed directly across C4 using proper probing technique to avoid ground-loop artifacts.

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

No - the MAX850ISA+ and MAX852ISA+ are not pin-compatible. While both use the same SO-8 package, pin 4 is SHDN on MAX850ISA+ but OSC (external clock input) on MAX852ISA+, and pin 5 is FB on MAX850ISA+ but unused on MAX852ISA+. Substituting them without PCB revision will result in non-functional shutdown control or incorrect feedback. The MAX850ISA+ and MAX851ISA+ are pin-compatible; MAX852ISA+ and MAX853ISA+ share a different pinout.

What is the maximum recommended flying capacitor value for the MAX850ISA+?

The MAX850ISA+ datasheet specifies 1µF ceramic capacitors for C1 and C2, with ESR ≤0.8Ω. Larger values do not improve performance and may degrade start-up time or cause instability due to increased charge time and parasitic inductance. Using >1µF capacitors can also increase inrush current stress on internal switches. The 1µF value is optimized for 100kHz operation, low profile, and minimal board area - deviating from this recommendation risks violating the device's specified dropout behavior and ripple performance.