Analog Devices Inc./Maxim Integrated MAX687CSA+T

Overview

The MAX687CSA+T from Maxim Integrated is a precision 3.3V fixed-output, low-dropout linear regulator IC that controls an external PNP pass transistor to deliver up to 1A output current. It features automatic latched shutdown at 2.96V output voltage, integrated power-fail monitoring (PFO), and 10mA base-drive capability-designed for battery-powered portable telephones and memory backup supplies where deep-discharge prevention is critical.

For engineers reviewing the MAX687CSA+T datasheet, MAX687CSA+T pinout, MAX687CSA+T application, or MAX687CSA+T equivalent, this page delivers verified technical context, exact pin functions, real-world dropout behavior (40mV @ 200mA), confirmed shutdown hysteresis (70mV), and validated alternatives with documented functional differences-not generic timing or power management claims.

Technical Context

The MAX687CSA+T implements a precision bandgap reference and dual comparators: one for power-fail detection (trip at 3.13V nominal −170mV = 2.96V) and another for latched shutdown. Its ON input requires a high pulse to initiate startup and remains active until VOUT exceeds 3.13V, ensuring reliable turn-on under marginal input conditions.

Base drive is delivered via the BASE pin with current limiting set by an external resistor between BASE and BLIM (IBASE ≤ 0.1V / (RB + 5Ω)). The PFO output actively sources and sinks current (not open-drain), enabling direct interface with logic-level reset circuits without pull-up resistors.

Key Specifications

Pinout & Package

MAX687CSA+T 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 low-dropout linear regulator applications.

Compared with MAX688CSA+T, the MAX687CSA+T provides autonomous battery-safe shutdown without firmware involvement; compared with LT1528CS8#PBF, it integrates PFO and latched control in a lower-dropout, lower-quiescent solution optimized for portable 3.3V systems.

Availability

MAX687CSA+T is available at Aetrix Electronics and suitable for portable telephones, battery-backed memory systems, and medical handheld devices requiring stable component supply across extended production lifecycles.

Supply support for MAX687CSA+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 and mixed-signal ICs for power, sensing, and communication applications.

The MAX687CSA+T belongs to Maxim's precision low-dropout linear regulator family, designed specifically for battery-powered equipment requiring autonomous power supervision, minimal quiescent current, and tight output voltage regulation without external feedback.

FAQ

What is the exact shutdown threshold voltage for the MAX687CSA+T?

The MAX687CSA+T enters latched shutdown when its regulated output falls to 2.96V. This threshold is guaranteed across temperature and load, with 70mV hysteresis to prevent chatter. The device remains off until the ON pin receives a clean high pulse-ensuring definitive, repeatable cutoff behavior critical for battery protection in portable telephones and memory backup systems using the MAX687CSA+T.

Does the MAX687CSA+T require an external PNP transistor, and which one is recommended?

Yes, the MAX687CSA+T requires an external PNP pass transistor to deliver load current. The Zetex FZT749 is the manufacturer-recommended device-guaranteeing ≥100 hFE and enabling >1A output with the MAX687CSA+T's 10mA base drive. Other qualified options include the 2N2907A and TIP42, but FZT749 delivers optimal dropout (40mV @ 200mA) and thermal performance in the MAX687CSA+T reference design.

How does the PFO output of the MAX687CSA+T differ from MAX688/MAX689 versions?

The MAX687CSA+T PFO is a push-pull output that both sources and sinks current, eliminating the need for an external pull-up resistor. In contrast, MAX688CSA+T and MAX689CSA+T use open-drain PFO outputs requiring external pull-ups. This active drive enables direct connection to microcontroller reset inputs or logic gates-simplifying circuit design and improving noise immunity in battery-powered applications using the MAX687CSA+T.

What is the minimum output capacitance required for stable operation of the MAX687CSA+T?

The MAX687CSA+T requires a minimum 10µF output capacitor (C2) for loads up to 100mA. For higher currents, the datasheet specifies 1µF per 10mA (e.g., 68µF for 500mA). Low-ESR capacitors-such as Sanyo OS-CON or Nichicon F95 series-are mandatory to ensure stability and transient response. Using undersized or high-ESR C2 risks oscillation and poor load-step recovery in the MAX687CSA+T circuit.

Can the MAX687CSA+T operate with input voltages below 3.3V?

No-the MAX687CSA+T cannot regulate at input voltages below its 3.3V output plus dropout voltage. With the FZT749 transistor, minimum VIN is 3.34V at 200mA (40mV dropout). At 1A, dropout rises to ~100mV, requiring VIN ≥ 3.4V. Below these thresholds, the output follows VIN minus VCE(SAT) of the PNP-so the MAX687CSA+T only delivers regulated 3.3V when VIN exceeds the dropout-dependent minimum.