Analog Devices Inc./Maxim Integrated MAX1681ESA+

Overview

MAX1681ESA+ from Maxim Integrated is a frequency-selectable switched-capacitor voltage converter configured as an inverting or doubling charge pump IC, delivering up to 125mA output current with 3.5Ω typical output resistance, 500kHz/1MHz selectable switching frequencies, and operation from +2.0V to +5.5V input - used for local negative supplies in op-amp biasing and interface power rails.

For engineers reviewing the MAX1681ESA+ datasheet, MAX1681ESA+ pinout, MAX1681ESA+ application, or MAX1681ESA+ equivalent, key selection considerations include its dual-mode configuration (inverter/doubler), low-quiescent shutdown (<1µA), SO-8 package compatibility, and capacitor-size optimization via FSEL-controlled frequency selection.

Technical Context

The MAX1681ESA+ implements a two-phase, non-regulated switched-capacitor topology with internal CMOS switches and no inductor. Its output polarity and gain are determined by external pin strapping: LV = GND enables inverter mode (VOUT ≈ –VIN); LV = OUT enables doubler mode (VOUT ≈ +2VIN).

Frequency selection is implemented via the FSEL pin: logic-low selects 1MHz (inverter) or 1MHz (doubler); logic-high selects 500kHz. The device lacks internal feedback regulation, so output voltage accuracy depends on load, input voltage, capacitor ESR, and switching frequency - all directly reflected in its 440mV drop at 125mA.

Key Specifications

Pinout & Package

MAX1681ESA+ is housed in an 8-pin SOIC (SO) package with standard 1.27mm pitch, JEDEC MS-012AC compliant, and rated for surface-mount reflow.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar switched-capacitor voltage converter applications.

Compared with MAX1680ESA+, the MAX1681ESA+ trades lower-light-load efficiency for 2.5× higher output current and 1µF capacitor support; versus MAX861ESA+, it adds shutdown, dual-mode flexibility, and 2.5× current capacity at the cost of larger SO-8 packaging.

Availability

MAX1681ESA+ is available at Aetrix Electronics and suitable for local negative supplies, interface power supplies, and op-amp power supplies requiring stable component supply across industrial temperature ranges and long-lifecycle production programs.

Supply support for MAX1681ESA+ 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, communications, and consumer applications.

The MAX1680/MAX1681 product line delivers high-current, capacitor-based DC-DC conversion for space-constrained systems needing inductor-free voltage inversion or doubling - targeting portable instrumentation, sensor interfaces, and embedded analog subsystems.

FAQ

What configuration modes does the MAX1681ESA+ support?

The MAX1681ESA+ supports two configuration modes: inverter mode (VOUT ≈ –VIN) when LV is strapped to GND, and doubler mode (VOUT ≈ +2VIN) when LV is strapped to OUT. Both modes use the same external capacitor network but differ in output polarity and gain. The MAX1681ESA+ does not support regulated output or adjustable voltage - output is determined solely by input voltage and topology.

How does the FSEL pin affect MAX1681ESA+ performance?

The FSEL pin on the MAX1681ESA+ selects between 500kHz (FSEL = high) and 1MHz (FSEL = low). At 1MHz, the MAX1681ESA+ achieves lower output impedance with smaller 1µF capacitors and reduced board area, but draws higher supply current. At 500kHz, it consumes less quiescent power and generates less high-frequency noise - ideal for noise-sensitive analog sections. The choice directly impacts capacitor size, efficiency, and EMI profile.

Can MAX1681ESA+ be used in shutdown mode during doubler operation?

No - shutdown mode is not functional in doubler configuration for the MAX1681ESA+. When LV = OUT (doubler mode), driving SHDN high does not disable the charge pump; the device remains active. To achieve low-power state in doubler applications, external enable control of the input supply or use of a different topology is required. Shutdown is fully supported only in inverter mode (LV = GND), where SHDN high pulls OUT to GND.

What is the maximum output current capability of MAX1681ESA+ under real-world conditions?

The MAX1681ESA+ delivers up to 125mA continuous output current in both inverter and doubler configurations, verified at TA = +25°C with 1µF low-ESR capacitors and VIN = 5V. At full load, output voltage drops by ~440mV due to its 3.5Ω typical output resistance. Derating applies at elevated temperatures or with higher-ESR capacitors - actual usable current may fall to ~100mA at +85°C with 2.2µF capacitors per the datasheet's thermal limits.

Is MAX1681ESA+ pin-compatible with MAX861ESA+?

No - MAX1681ESA+ is not pin-compatible with MAX861ESA+. Although both are 8-pin charge pumps, MAX861ESA+ uses a µMAX-8 package with different pinout (e.g., no LV or FSEL pins), lacks shutdown functionality, and delivers only 50mA. The MAX1681ESA+ uses SO-8 packaging and features dedicated FSEL, LV, and SHDN pins absent in MAX861ESA+. Direct replacement would require PCB redesign and firmware updates for control logic.