Analog Devices Inc./Maxim Integrated MAX688CUA-T

Overview

The MAX688CUA-T from Maxim Integrated is a precision 3.3V fixed-output, low-dropout linear regulator requiring an external PNP pass transistor (e.g., FZT749) to deliver >1A output current. It features active-low shutdown control (SHDN), power-fail monitoring (PFO), ±2% output accuracy, and operates from 2.7V to 11.0V input. Designed for battery-powered portable telephones and memory backup supplies where controlled power sequencing and low-quiescent-current standby are critical.

For engineers reviewing the MAX688CUA-T datasheet, MAX688CUA-T pinout, MAX688CUA-T application, or MAX688CUA-T equivalent, this page delivers verified technical context, real-world dropout behavior at 200mA/650mA/4A, SHDN threshold hysteresis (70mV), PFO trip point (170mV below nominal), and µMAX-8 package–specific layout guidance - all confirmed from Maxim's official 1994 datasheet and ordering information.

Technical Context

The MAX688CUA-T implements a precision bandgap reference and high-gain error amplifier driving an external PNP transistor via BASE pin with ≥10mA base-current capability. Its SHDN input enables three-state operation: ON (>1.25V), standby (<1.2V, <25µA supply), and full shutdown (<0.2V, <1µA). The PFO comparator monitors VOUT continuously and asserts open-drain low when output drops 170mV below 3.3V nominal.

Dropout voltage is determined solely by the external PNP's V_CE(SAT); typical values are 40mV at 200mA (FZT749), 100mV at 650mA, and 0.8V at 4A. Base-current limiting via RB resistor between BASE and BLIM ensures accurate current limiting without collector-sense resistors - critical for maintaining low dropout while protecting against overload.

Key Specifications

Pinout & Package

MAX688CUA-T is housed in an 8-pin µMAX package - a miniature surface-mount SO variant with exposed pad for thermal enhancement. Pin 1 is IN (input voltage), pin 2 is SHDN (active-low shutdown), pin 3 is PFO (open-drain power-fail output), pin 4 is GND, pin 5 is OUT (3.3V regulated output), pin 6 is BLIM (base-current limit), pin 7 is BASE (PNP base drive), and pin 8 is CC (compensation capacitor connection).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar low-dropout linear regulator applications.

Compared with MAX687CUA-T, the MAX688CUA-T offers externally controllable shutdown without latching - enabling dynamic power cycling by host firmware. Against MAX689CUA-T, it provides 3.3V output with higher PFO trip voltage, simplifying interface to 3.3V-tolerant supervisors while retaining identical package and control logic.

Availability

MAX688CUA-T is available at Aetrix Electronics and suitable for portable telephones, battery-powered memory backup systems, and portable test instruments requiring stable component supply with guaranteed long-term availability and traceable sourcing.

Supply support for MAX688CUA-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 MAX687/MAX688/MAX689 family was designed specifically for high-accuracy, low-dropout regulation in battery-critical portable equipment - leveraging external PNP transistors to decouple thermal management from the control IC while delivering precise 3.0V/3.3V outputs with intelligent power-fail monitoring.

FAQ

What is the maximum output current supported by the MAX688CUA-T?

The MAX688CUA-T itself does not source output current - it drives an external PNP pass transistor. With a high-gain device like the FZT749 (β > 100), the MAX688CUA-T can support >1A output. Using a pseudo-Darlington configuration (e.g., TIP42 + 2N4403), output currents up to 4A are achievable. Actual capability depends on transistor selection, heatsinking, and dropout voltage constraints.

Does the MAX688CUA-T have automatic shutdown like the MAX687CUA-T?

No. The MAX688CUA-T does not include automatic latched shutdown based on output voltage. Instead, it uses the SHDN pin for external control: pulling SHDN below 0.2V fully shuts down the device (<1µA), while voltages between 1.2V and 1.25V place it in low-current standby (<25µA). This differs fundamentally from the MAX687CUA-T's autonomous 2.96V-triggered latch-off behavior.

What is the function of the BLIM pin on the MAX688CUA-T?

The BLIM pin on the MAX688CUA-T works with the BASE pin to implement programmable base-current limiting. A resistor (RB) connected between BASE and BLIM sets the maximum base drive: I_BASE ≤ 0.1V / (RB + 5Ω). This protects the external PNP transistor during overload or dropout conditions and provides predictable output current limiting without adding series resistance in the collector path.

Can the MAX688CUA-T be used with ceramic output capacitors?

Yes - but only low-ESR ceramic capacitors meeting the minimum 10µF requirement (e.g., X5R/X7R, ≥1206 size) are recommended. The MAX688CUA-T's compensation relies on C2's ESR being <1% of load resistance; standard ceramics often have near-zero ESR, which may cause instability. If using ceramics, add a small series resistor (e.g., 10–50mΩ) or select specialty low-ESR polymer-ceramic hybrids verified for LDO stability.

What is the purpose of the CC pin on the MAX688CUA-T?

The CC pin on the MAX688CUA-T connects to a 10nF non-polarized compensation capacitor (e.g., ceramic or polyester) tied to GND. This capacitor stabilizes the control loop, eliminates startup overshoot, and improves transient response. Aluminum or tantalum electrolytics are unsuitable due to leakage current (>25nA), which shifts output voltage and PFO thresholds. Proper CC placement is critical for reliable 3.3V regulation.