Analog Devices Inc./Maxim Integrated MAX881REUB+T

Overview

MAX881REUB+T from Maxim Integrated is a low-noise, inverting charge-pump power supply with integrated negative linear regulator, designed specifically to bias GaAsFET power amplifiers in portable wireless transceivers. It accepts 2.5V–5.5V input, delivers up to 4mA at preset −2.0V or adjustable −0.5V to (−VIN + 0.6V), and achieves 1mV_p-p output ripple and noise. Its POK signal enables controlled GaAsFET drain switching.

For engineers reviewing the MAX881REUB+T datasheet, MAX881REUB+T pinout, MAX881REUB+T application, or MAX881REUB+T equivalent, this device is selected for ultra-low-noise GaAsFET biasing where startup timing, shutdown current (<1µA), and regulated negative voltage stability under load are critical design constraints.

Technical Context

The MAX881REUB+T integrates a capacitive charge pump followed by an N-channel pass transistor-based linear regulator. The charge pump generates unregulated negative voltage at NEGOUT, which the linear regulator filters and regulates at OUT with 2mV/mA load regulation and 2Ω output impedance in regulation mode.

Its POK output is an active-low open-drain signal asserting when OUT reaches 92.5% of its setpoint; SHDN is an active-low logic input enabling shutdown with 1ms guaranteed startup and <0.05µA quiescent current. Oscillation frequency is fixed at 100kHz ±20kHz.

Key Specifications

Pinout & Package

The MAX881REUB+T is housed in a 10-pin µMAX package (3.0mm × 3.0mm × 0.8mm, 0.5mm pitch), thermally enhanced for portable RF applications.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar GaAsFET bias supply applications.

Compared with MAX882REUB+T and LM2662M/NOPB, the MAX881REUB+T uniquely combines −2.0V precision regulation, 1mV_p-p noise, and integrated POK sequencing in a 10-pin µMAX package - making it the only option qualified for production GaAsFET bias in cellular handsets requiring guaranteed startup and low-noise stability.

Availability

MAX881REUB+T is available at Aetrix Electronics and suitable for cellular handsets, wireless modems, and two-way pagers requiring stable component supply, long-term lifecycle support, and consistent parametric performance across temperature.

Supply support for MAX881REUB+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 U.S.-based semiconductor company specializing in high-performance analog, mixed-signal, and power management ICs for industrial, communications, and consumer applications.

The MAX881R product line was engineered specifically for low-noise, sequenced GaAsFET bias in portable wireless transceivers - addressing RF front-end requirements for GSM, PCS, PHS, and early 3G handsets.

FAQ

What is the maximum output current capability of the MAX881REUB+T?

The MAX881REUB+T delivers up to 4mA of continuous output current at its regulated negative output (OUT). This is sufficient for biasing most GaAsFET power amplifiers used in cellular handsets and wireless modems. Output current capability varies with input voltage and temperature; at VIN = 2.5V and TA = +85°C, maximum load is reduced to ~2.5mA while maintaining 1mV_p-p ripple. The MAX881REUB+T datasheet specifies 4mA as the guaranteed minimum across the full operating range.

How does the POK signal function in the MAX881REUB+T?

The POK (Power-OK) signal in the MAX881REUB+T is an active-low, open-drain output that goes low when the regulated output voltage (OUT) reaches 92.5% of its final setpoint. It remains low until OUT stabilizes within specification. This signal is intended to control an external P-MOSFET switch on the GaAsFET drain, ensuring the PA is not powered until proper gate bias is established. A pull-up resistor ≥50kΩ is required on the POK line to ensure correct logic-high assertion. The MAX881REUB+T does not include internal pull-up.

Can the MAX881REUB+T generate output voltages other than −2.0V?

Yes, the MAX881REUB+T supports adjustable output voltages from −0.5V to (−VIN + 0.6V) using the FB (feedback) pin. When FB is grounded, the device operates in fixed −2.0V mode. To adjust, connect FB to the midpoint of a resistor divider between OUT and GND. For example, with R1 = 200kΩ and R2 = 190kΩ, V_OUT ≈ −1.9V. The MAX881REUB+T datasheet provides the formula R2 = R1(2 × |V_OUT| − 1) and recommends 1% tolerance resistors for accuracy.

What capacitor values are required for stable operation of the MAX881REUB+T?

The MAX881REUB+T requires four external capacitors: three 0.22µF low-ESR ceramic capacitors (C1, C2, C3) and one 4.7µF low-ESR ceramic or chip tantalum capacitor (C4). C1 and C2 form the charge-pump flying network; C3 decouples the linear regulator input (NEGOUT); C4 filters the regulated output (OUT). ESR must be ≤0.4Ω for C1–C3 and ≤0.1Ω for C4. Larger values (e.g., 1µF/10µF) reduce noise further but increase cost and board area. All capacitors must be placed close to the MAX881REUB+T pins per layout guidelines.

Does the MAX881REUB+T require a minimum input voltage to maintain regulation at full load?

Yes, the MAX881REUB+T requires the input voltage (VIN) to be at least 0.6V higher than the absolute magnitude of the desired output voltage to maintain regulation at full 4mA load. For example, to sustain −2.0V at 4mA, VIN must be ≥2.6V. The absolute minimum VIN is 2.5V regardless of output setting, but below VIN = (|V_OUT| + 0.6V), the device enters dropout and load regulation degrades. This relationship is confirmed in Figure TOC04 of the MAX881REUB+T datasheet.