Analog Devices Inc./Maxim Integrated MAX688CPA

Overview

MAX688CPA 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), 150µA operating supply current, and ±2% output voltage accuracy over 0°C to +70°C. Used in battery-powered portable telephones and memory backup supplies where controlled power sequencing and low-voltage cutoff are critical.

For engineers reviewing the MAX688CPA datasheet, MAX688CPA pinout, MAX688CPA application, or MAX688CPA equivalent, this page delivers verified technical context, validated pin functions, real-world dropout behavior at 200mA/650mA/4A, confirmed PFO threshold (170mV below nominal), and precise SHDN hysteresis (70mV) - all essential for reliable low-power system design and BOM validation.

Technical Context

The MAX688CPA implements a precision bandgap reference and dual comparators: one monitors VOUT for PFO assertion at 170mV below nominal (3.13V), another controls SHDN transitions with 1.2V standby and 0.2V full-shutdown thresholds. Its base-drive circuit delivers ≥10mA to the external PNP, enabling high-current regulation without internal pass devices.

Dropout voltage is determined solely by the external PNP's V_CE(SAT), not internal circuitry: 40mV at 200mA (FZT749), 100mV at 650mA, and 0.8V at 4A. The BLIM–BASE resistor network limits base current to prevent quiescent current runaway during dropout while preserving low-V_CE(SAT) operation.

Key Specifications

Pinout & Package

MAX688CPA is housed in an 8-pin plastic DIP package (0.300" wide), with lead finish Sn/Pb, RoHS-compliant per Maxim's 1994 specification. Pin spacing is 0.100", body dimensions 0.300" × 0.400".

Key Features

Applications

Equivalent & Alternatives

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

Compared with LT1528CS8#PBF and TPS76333DBVR, the MAX688CPA uniquely combines external PNP scalability (>1A), precision PFO (170mV trip), and three-threshold SHDN control - making it irreplaceable in battery-critical applications demanding both high current and deterministic low-voltage shutdown behavior.

Availability

MAX688CPA is available at Aetrix Electronics and suitable for portable telephones, battery-powered instruments, and memory backup supplies requiring stable component supply, long-term lifecycle support, and traceable sourcing for industrial OEM programs.

Supply support for MAX688CPA 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 and mixed-signal ICs for power management, sensing, and interface applications, with emphasis on high-reliability industrial and portable systems.

The MAX687/MAX688/MAX689 product line was engineered specifically for high-accuracy, low-dropout regulation in battery-constrained equipment - delivering fixed 3.0V/3.3V outputs with external PNP flexibility, PFO monitoring, and multi-level shutdown control.

FAQ

What is the exact dropout voltage specification for MAX688CPA at 500mA load?

The MAX688CPA itself does not define a fixed dropout voltage - it depends entirely on the external PNP transistor's V_CE(SAT). With FZT749, typical dropout is 100mV at 650mA and 40mV at 200mA. At 500mA, measured data shows ~75mV using FZT749 under standard test conditions (C2 = 20µF, TA = +25°C). This value scales with PNP selection and thermal conditions.

Does MAX688CPA have automatic shutdown like MAX687CPA?

No. The MAX688CPA has no automatic output-voltage-triggered shutdown. It relies exclusively on the active-low SHDN pin for control: pulling SHDN below 1.2V enters standby mode (<25µA), and below 0.2V fully shuts down (<1µA). Unlike the MAX687CPA, it does not latch off when VOUT falls below 2.96V - that function is exclusive to MAX687.

What is the guaranteed PFO trip voltage tolerance for MAX688CPA?

The MAX688CPA PFO trips when VOUT falls 170mV below nominal 3.3V - i.e., at 3.13V - with a guaranteed tolerance of ±7mV (hysteresis), per Electrical Characteristics table. This is specified at I_BASE = 1mA and applies across the full temperature range (0°C to +70°C) and input voltage range (3.5V–11.0V).

Can MAX688CPA drive a 4A load, and what transistor is recommended?

Yes - the MAX688CPA can drive up to 4A when paired with a suitable PNP configuration. Figure 3 in the datasheet shows a pseudo-Darlington circuit using TIP42 (Q1) and 2N4403 (Q2) with BASE tied to BLIM. At 4A, dropout reaches 0.8V (VIN–VOUT), requiring thermal management. FZT749 alone supports >1A; higher currents demand compound or heatsinked solutions.

What compensation capacitor value is recommended for MAX688CPA, and why?

A 10nF non-polarized capacitor (e.g., ceramic or polyester) is recommended between CC and GND for the MAX688CPA. This value optimally balances transient response and startup overshoot suppression. Larger values (up to 100nF) reduce overshoot further but increase power-up time; aluminum/tantalum electrolytics are prohibited due to leakage current shifting output voltage and PFO thresholds.