Analog Devices Inc./Maxim Integrated MAX640ESA

Overview

MAX640ESA from Maxim Integrated is a 3.3V fixed-output, high-efficiency step-down DC-DC switching regulator with pulse-frequency-modulated (PFM) control, 10µA quiescent current, 225mA output capability, and -40°C to +85°C operating range. It integrates a 1A PMOS power switch and features low-battery detection for portable 9V-to-3.3V conversion in battery-powered instrumentation.

For engineers reviewing the MAX640ESA datasheet, MAX640ESA pinout, MAX640ESA application, or MAX640ESA equivalent, key selection criteria include its PFM efficiency profile across light-to-moderate loads, preset 3.3V output without external feedback resistors, SO-8 package compatibility with space-constrained PCB layouts, and integrated low-battery comparator with 1.28V threshold.

Technical Context

The MAX640ESA uses current-limiting PFM control to maintain high efficiency from 10µA to 225mA load currents-avoiding the 2–10mA quiescent draw of PWM regulators. Its internal 1A PMOS switch operates with variable on-time (t_ON = 50µs × V_IN/(V_IN − V_OUT)) and minimum off-time (t_OFF ≥ 50µs × V_IN/V_OUT) to sustain constant peak inductor current.

It supports fixed 3.3V output when VFB is grounded or adjustable output via external resistor divider, while retaining active low-battery detection (LBI/LBO) and shutdown control (SHDN) independent of regulation state-enabling system-level power management in portable devices.

Key Specifications

Pinout & Package

MAX640ESA is housed in an 8-pin SO (Small Outline) package per JEDEC MS-012, 150-mil body width, with exposed pad not connected internally.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar step-down DC-DC converter applications.

Compared with TPS62231DRYR and LT1931ES5#TRMPBF, the MAX640ESA delivers superior light-load efficiency and longer battery life in 4–11.5V input systems where 225mA and fixed 3.3V are sufficient-without demanding high-frequency magnetics or accepting higher idle power.

Availability

MAX640ESA is available at Aetrix Electronics and suitable for portable instrumentation, handheld terminals, industrial sensor nodes, and battery-powered analog front-ends requiring stable component supply with long-lifecycle support.

Supply support for MAX640ESA 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, mixed-signal, and power-management ICs for industrial, medical, and communications applications.

The MAX639/MAX640/MAX653 family was engineered specifically for high-efficiency, low-quiescent-current DC-DC conversion in portable and battery-critical systems-prioritizing PFM operation, integrated power switches, and system-level monitoring features like low-battery detection.

FAQ

What is the guaranteed output voltage accuracy of the MAX640ESA over temperature and load?

The MAX640ESA guarantees 3.3V output within ±3% (3.17V to 3.43V) across full operating conditions: -40°C to +85°C, 0–100mA load, and 4.0–11.5V input. This specification is validated per Electrical Characteristics table on page 2 of the datasheet, with typical deviation <±1% at +25°C and 100mA.

Can the MAX640ESA be used in an inverting configuration to generate a negative output voltage?

Yes-the MAX640ESA supports inverting operation per Figure 6 in the datasheet: tie the nominal output node to system ground, connect V+ to battery, and route the IC's GND pin to the negative output rail. This yields -3.3V with efficiency up to 87% at 10mA (Figure 8), provided differential voltage between V+ and VOUT stays ≤11.5V.

Does the low-battery detection circuit remain functional when the MAX640ESA is in shutdown mode?

Yes-the low-battery comparator remains fully active during shutdown. When SHDN is pulled low, the LX switch disables and VOUT collapses, but the LBI input continues monitoring battery voltage and drives LBO low if LBI falls below 1.28V. This allows host systems to detect end-of-life even when the main regulator is disabled.

What is the recommended inductor value and saturation current rating for the MAX640ESA at 225mA output?

For 225mA continuous output, use a ≥100µH inductor rated for ≥600mA peak current (4× I_{OUTMAX). Inductor series resistance should be <0.5Ω to minimize dropout and maintain efficiency. Recommended parts include Sumida CDR74-100 or Coilcraft MSS1270-104, both validated in Maxim's Typical Operating Characteristics.}

Is an external diode required for MAX640ESA operation, and what type is specified?

Yes-an external Schottky diode is mandatory. The datasheet specifies the 1N5817 (or equivalent) due to its 0.55V forward voltage and fast recovery. Signal diodes (e.g., 1N4148) suffice only below 100mA peak; general-purpose rectifiers (e.g., 1N4001) are prohibited due to slow turn-off causing excessive losses and potential IC damage.