Analog Devices Inc./Maxim Integrated MAX861ESA+

Overview

MAX861ESA+ from Maxim Integrated is a frequency-selectable, 50mA switched-capacitor voltage converter that inverts +1.5V to +5.5V inputs or doubles +2.5V to +5.5V inputs. It operates at three user-selectable switching frequencies (13/100/250 kHz), delivers 87% efficiency at 50mA load, and features 12Ω output resistance and 1µA shutdown current. It serves as a compact, inductorless power supply for portable medical instruments and handheld test equipment.

For engineers reviewing the MAX861ESA+ datasheet, MAX861ESA+ pinout, MAX861ESA+ application, or MAX861ESA+ equivalent, key selection criteria include its -40°C to +85°C operating range, SO-8 package compatibility, inverter/doubler mode flexibility via LV pin, and trade-offs between capacitor size, quiescent current, and EMI sensitivity across its three FC-selectable frequencies.

Technical Context

The MAX861ESA+ implements a BiCMOS charge-pump architecture with direct oscillator-to-switch coupling (no frequency division), enabling precise control of switching frequency via the FC pin. Its internal switch resistance (~8Ω) combines with external capacitor ESR to determine total output resistance (typically 12Ω with 0.2Ω ESR caps).

Operation supports two distinct configurations: inverter mode (LV = GND) delivering –VIN output, and doubler mode (LV = OUT) delivering +2VIN output. Shutdown is active-low on the SHDN pin, reducing supply current to <1µA while preserving stateless operation-no sequencing or biasing required for wake-up.

Key Specifications

Pinout & Package

MAX861ESA+ is housed in an 8-pin SO (Small Outline) package per outline S8-4, RoHS-compliant, with 1.27mm pitch and standard JEDEC MS-012AC footprint.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX860ESA+, MAX861ESA+ offers higher base switching frequencies for smaller capacitors and better EMI management, while MAX660CPA+ provides greater output current and lower output resistance at the cost of fixed frequency and larger solution size.

Availability

MAX861ESA+ is available at Aetrix Electronics and suitable for portable medical instruments, hand-held test equipment, operational-amplifier power supplies, and interface power supplies requiring stable component supply across extended temperature ranges.

Supply support for MAX861ESA+ 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, mixed-signal, and power-management ICs for industrial, medical, and communications applications.

The MAX860/MAX861 product line was designed specifically to replace legacy charge pumps like the ICL7660 with higher efficiency, wider input range, and flexible frequency control-targeting space- and power-constrained portable electronics.

FAQ

What are the valid switching frequencies for MAX861ESA+ and how are they selected?

The MAX861ESA+ supports three nominal switching frequencies: 13kHz (FC = VDD), 100kHz (FC = GND), and 250kHz (FC = OUT). These values are confirmed in Table 1 of the datasheet and apply specifically to the MAX861 variant. Selection is made by hard-wiring the FC pin to the appropriate voltage node-no external clock or configuration register is involved. Each frequency directly impacts capacitor sizing, quiescent current, and EMI profile.

Can MAX861ESA+ be used as a voltage doubler, and what is required to configure it?

Yes, MAX861ESA+ can operate as a positive voltage doubler. To configure it, connect the LV pin to the OUT pin (not GND). In this mode, the device accepts +2.5V to +5.5V input and delivers approximately +2×VIN at the OUT pin. The electrical characteristics-including output current, efficiency, and frequency behavior-remain consistent with inverter mode except for the expanded input voltage range and slightly higher no-load supply current.

What is the output resistance of MAX861ESA+ and how does it affect load regulation?

The MAX861ESA+ has a typical output resistance of 12Ω, as specified in the Electrical Characteristics table under "Output Resistance" (ROUT). This value includes internal switch resistance (~8Ω) and contributions from external capacitor ESR. At 50mA load, this results in ~0.6V output droop from the ideal inverted or doubled voltage-e.g., –5.0V becomes –4.4V. Designers must account for this linear drop when specifying output voltage tolerances.

Is MAX861ESA+ pin-compatible with the ICL7660 or MAX660, and what modifications are needed?

MAX861ESA+ is footprint-compatible with the ICL7660 and MAX660 in SO-8 packages, but pin functions differ: Pin 7 is SHDN (not OSC), and Pin 6 is LV (not NC). To retrofit, tie SHDN to VDD (not float), and connect LV to GND (inverter) or OUT (doubler). FC (Pin 1) may remain unconnected (defaults to 13kHz) or be wired to select frequency-no changes needed for basic operation.

What is the minimum input voltage required for MAX861ESA+ in inverter mode?

The minimum input voltage for MAX861ESA+ in inverter mode is +1.5V, as explicitly stated in the General Description and Electrical Characteristics tables. Operation below this voltage is not guaranteed and may result in failure to start or unstable output. This 1.5V lower limit enables use with single-cell alkaline or NiMH batteries, distinguishing it from the MAX660 (2.0V min) and ICL7660 (1.5V min but only 10mA output).