Analog Devices Inc./Maxim Integrated MAX861ISA

Overview

MAX861ISA from Maxim Integrated is a frequency-selectable, 50mA switched-capacitor voltage inverter/doubler IC operating from +1.5V to +5.5V (inverter) or +2.5V to +5.5V (doubler), delivering up to –5.5V output or +11V output with <12Ω output resistance and 87% efficiency at 50mA load - used in portable medical instruments and handheld test equipment requiring compact, inductorless negative/positive rail generation.

For engineers reviewing the MAX861ISA datasheet, MAX861ISA pinout, MAX861ISA application, or MAX861ISA equivalent, key selection criteria include its three selectable switching frequencies (13/100/250 kHz), 1µA shutdown current, SO-8 package compatibility, and direct replacement capability for legacy ICL7660-based designs with minimal board changes.

Technical Context

The MAX861ISA implements a BiCMOS charge-pump architecture with internal flying-capacitor switches driven directly at oscillator frequency-no frequency division-enabling precise control of output polarity via LV pin configuration (GND for inverter, OUT for doubler). Its FC pin selects one of three discrete switching frequencies without external components.

It operates in two distinct modes: inverting mode delivers –V_IN with input range +1.5V to +5.5V; doubling mode delivers +2×V_IN with input range +2.5V to +5.5V. Shutdown is active-low on pin 7 (–S-H-D-N–), reducing supply current to <1µA while preserving state.

Key Specifications

Pinout & Package

MAX861ISA is housed in an 8-pin SO (Small Outline) package per outline S8-4, 21-0041, with standard 1.27mm pitch and RoHS-compliant finish.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX860ISA, the MAX861ISA provides higher-frequency options enabling smaller external capacitors and better ripple performance, while ICL7660CPA remains viable only for low-current, non-portable applications where efficiency and size are secondary.

Availability

MAX861ISA is available at Aetrix Electronics and suitable for portable medical instruments, hand-held test equipment, interface power supplies, operational-amplifier power supplies, and portable computers requiring stable component supply across industrial temperature ranges.

Supply support for MAX861ISA 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 inductor-based and legacy charge-pump solutions in space-constrained, battery-powered systems demanding efficient, compact, and flexible voltage inversion or doubling.

FAQ

What is the maximum output current specification for the MAX861ISA?

The MAX861ISA is rated for 50mA continuous output current in both inverter and doubler configurations. This rating assumes proper capacitor selection (e.g., 4.7µF–10µF low-ESR ceramics), ambient temperature ≤+85°C, and adequate PCB copper area for thermal dissipation. Peak transient current may reach 60mA briefly, but sustained operation above 50mA risks exceeding thermal limits and degrading efficiency or long-term reliability. The MAX861ISA datasheet specifies 50mA as the guaranteed continuous output under standard test conditions.

How does the FC pin configure switching frequency on the MAX861ISA?

The FC pin on the MAX861ISA selects one of three discrete switching frequencies: connecting FC to VDD sets 13kHz, to GND sets 100kHz, and to OUT sets 250kHz. These values are device-specific - the MAX861ISA differs from the MAX860ISA, which uses 6/50/130kHz. The FC pin draws negligible current (<4µA), allowing direct connection to VDD, GND, or OUT without buffering. Frequency selection directly impacts capacitor sizing, output ripple, and quiescent current - higher frequencies reduce required C1/C2 values but increase supply current.

Can the MAX861ISA operate as both an inverter and a doubler on the same board?

Yes - the MAX861ISA supports both inverter and doubler modes via the LV pin: LV = GND configures inverter mode (output = –V_IN); LV = OUT configures doubler mode (output = +2×V_IN). A single MAX861ISA cannot generate both outputs simultaneously, but two devices can be combined - one as inverter, one as doubler - to create a ±V_OUT supply. In such a combined circuit (Figure 3 of the datasheet), total load current across both outputs must not exceed 60mA, and LV pins must be correctly tied per mode to ensure stable operation of each stage.

What is the shutdown behavior of the MAX861ISA and how is it controlled?

The MAX861ISA features an active-low shutdown input (–S-H-D-N–, Pin 7) that reduces supply current to <1µA when pulled below 0.3V. During shutdown, internal switching ceases and the output floats - no active regulation or discharge path is provided. In inverter mode, loads between OUT and GND are unpowered; in doubler mode, loads between VDD and GND are unpowered. To enable normal operation, –S-H-D-N– must be pulled to VDD (inverter) or GND (doubler); leaving it floating is not permitted and may cause undefined behavior.

Is the MAX861ISA pin-compatible with the ICL7660 or MAX660?

The MAX861ISA is not fully pin-compatible with the ICL7660 or MAX660 due to functional pin reassignment: Pin 7 is –S-H-D-N– (shutdown) on MAX861ISA versus OSC (oscillator output) on ICL7660/MAX660, and Pin 1 is FC (frequency control) versus OSC (input/output) on legacy parts. However, the MAX861ISA can be socketed into existing ICL7660/MAX660 layouts with one wiring change - jumpering Pin 7 to VDD (inverter) or GND (doubler) - while retaining all other connections. No PCB redesign is needed beyond this single modification.