Analog Devices Inc./Maxim Integrated MAX688CSA

Overview

MAX688CSA from Maxim Integrated is a precision 3.3V fixed-output, low-dropout linear regulator requiring an external PNP pass transistor; it delivers up to 1A output current with 40mV dropout at 200mA (FZT749), features active-low shutdown control (SHDN), power-fail monitoring (PFO), and operates from 2.7V to 11.0V input; used in portable telephones and battery-powered instrumentation where regulated 3.3V supply with early voltage warning is critical.

For engineers reviewing the MAX688CSA datasheet, MAX688CSA pinout, MAX688CSA application, or MAX688CSA equivalent, this page provides verified technical context, confirmed pin functions, real-world dropout behavior, PFO threshold accuracy (170mV below nominal), and validated alternative options for 3.3V low-dropout regulator designs with external pass transistors.

Technical Context

The MAX688CSA implements a precision bandgap reference and dual comparators: one monitors VOUT for PFO assertion at 170mV below 3.3V (VPFT = 3.13V), and another controls SHDN transitions with ±2% threshold accuracy (1.25V ON, 1.2V standby entry, 0.2V full shutdown). Its base-drive circuit delivers ≥10mA to the external PNP, enabling >1A output when β > 100.

Shutdown is three-level: normal operation (SHDN > 1.25V), standby (<1.2V, I_IN < 25µA), and full shutdown (<0.2V, I_IN < 1µA); PFO is open-drain and sinks current only; compensation is set via CC pin with 10nF–100nF non-polarized capacitor to stabilize loop response and suppress start-up overshoot.

Key Specifications

Pinout & Package

MAX688CSA is housed in an 8-pin SO (Small Outline) package, 3.9mm × 4.9mm body, 1.27mm pitch, RoHS-compliant, rated for 0°C to +70°C operation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 3.3V low-dropout regulator applications.

Compared with LT1528CS8#PBF and TPS76333DBVR, the MAX688CSA uniquely combines external PNP scalability (>1A), precision PFO (3.13V trip), and three-level SHDN for battery-aware power sequencing-making it optimal for portable systems demanding both high current and intelligent voltage supervision.

Availability

MAX688CSA is available at Aetrix Electronics and suitable for portable telephones, battery-powered instruments, and memory backup supplies requiring stable component supply with guaranteed long-term sourcing and industrial temperature-grade alternatives.

Supply support for MAX688CSA 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 MAX687/MAX688/MAX689 family was designed specifically for high-accuracy, low-dropout linear regulation in battery-powered equipment, emphasizing external PNP flexibility, precision voltage monitoring, and ultra-low shutdown current.

FAQ

What is the maximum output current supported by the MAX688CSA?

The MAX688CSA itself does not deliver output current directly-it drives an external PNP pass transistor. With a high-gain transistor like the FZT749 (β > 100), the MAX688CSA's ≥10mA base drive enables >1A output current. Actual maximum depends on the selected PNP's β, power dissipation rating, and heatsinking; the datasheet confirms 650mA with 100mV dropout and 4A capability in pseudo-Darlington configurations.

Does the MAX688CSA have automatic shutdown like the MAX687?

No, the MAX688CSA does not feature automatic latched shutdown. Unlike the MAX687-which shuts down when VOUT drops below 2.96V-the MAX688CSA relies solely on its active-low SHDN pin for control. It offers three distinct states: normal operation (SHDN > 1.25V), standby (<1.2V, I_IN < 25µA), and full shutdown (<0.2V, I_IN < 1µA), all user-controllable without voltage-dependent latching.

What is the function of the CC pin on the MAX688CSA?

The CC pin on the MAX688CSA is the compensation capacitor terminal. A 10nF–100nF non-polarized capacitor (e.g., ceramic or polyester) must be connected from CC to GND to stabilize the control loop, prevent oscillation, and eliminate start-up overshoot. Aluminum or tantalum electrolytics are unsuitable due to leakage current, which shifts output voltage and PFO thresholds.

Can the MAX688CSA be used with a P-channel MOSFET instead of a PNP transistor?

No, the MAX688CSA is designed exclusively for NPN-driven PNP pass transistors. Its BASE pin sinks current to turn on the PNP's base-emitter junction. A P-channel MOSFET requires gate-source voltage control (V_GS) and lacks the bipolar current-driving architecture needed for the MAX688CSA's base-current-limiting scheme (BLIM/BASE resistor network). Using a PMOS would require external level-shifting and gate drivers incompatible with the MAX688CSA's topology.

What is the PFO output configuration on the MAX688CSA?

The PFO output on the MAX688CSA is an open-drain structure that only sinks current. It asserts low when VOUT falls 170mV below nominal (i.e., at 3.13V for 3.3V output) and remains low during shutdown. An external pull-up resistor is required to generate a logic-high signal when PFO is inactive. This differs from the MAX687, which sources and sinks current on PFO.