Analog Devices Inc./Maxim Integrated MAX861CSA

Overview

MAX861CSA from Maxim Integrated is a frequency-selectable switched-capacitor voltage converter that inverts +1.5V to +5.5V inputs to negative outputs or doubles +2.5V to +5.5V inputs to positive outputs, delivering up to 50mA with 12Ω output resistance and 87% efficiency at full load - used in portable medical instruments and handheld interface power supplies.

For engineers reviewing the MAX861CSA datasheet, MAX861CSA pinout, MAX861CSA application, or MAX861CSA equivalent, key selection criteria include switching-frequency configurability (13/100/250 kHz), shutdown current <1µA, low-quiescent operation (200µA typical), and SO-8 package compatibility with legacy ICL7660/MAX660 footprints.

Technical Context

The MAX861CSA implements a charge-pump topology with direct oscillator-driven switches (no frequency division), enabling selectable fundamental switching frequencies of 13kHz, 100kHz, or 250kHz via the FC pin. Its LV pin configures mode: grounded for inversion, connected to OUT for doubling.

Output regulation is unregulated but load-stable due to 12Ω effective source resistance (including 8Ω internal switch resistance and capacitor ESR contributions). Shutdown disables all active circuitry, reducing supply current to <1µA while preserving reverse-current paths depending on load connection.

Key Specifications

Pinout & Package

MAX861CSA is housed in an 8-pin SOIC package (3.9mm × 4.9mm, 1.27mm pitch), RoHS-compliant and compatible with standard SO-8 reflow profiles.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX860CSA and MAX660CPA, the MAX861CSA offers the highest switching frequency option (250kHz) for minimal capacitor size, maintains identical SO-8 packaging for drop-in replacement in space-constrained layouts, and provides finer frequency granularity than the MAX660's dual-frequency architecture.

Availability

MAX861CSA is available at Aetrix Electronics and suitable for portable medical instruments, hand-held test equipment, interface power supplies, and operational-amplifier power supplies requiring stable component supply across industrial temperature ranges and long production lifecycles.

Supply support for MAX861CSA 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 and power management ICs for demanding industrial, medical, and communications applications.

The MAX860/MAX861 product line delivers inductorless voltage conversion for space- and noise-sensitive portable systems, targeting applications where traditional switching regulators introduce unacceptable EMI or board-area penalties.

FAQ

What is the maximum output current specification for the MAX861CSA?

The MAX861CSA is rated for a continuous output current of 50mA. This value is confirmed across inverter and doubler modes under specified conditions (e.g., VDD = +5V, FC = GND, C1 = C2 = 10µF, TA ≤ +85°C). At 50mA load, output voltage droop is defined by the 12Ω output resistance - for example, −4.4V output from a +5V input in inverter mode. Exceeding 50mA risks thermal overload and reduced efficiency, and absolute maximum rating limits output short-circuit duration to 1 second.

How does the FC pin configure switching frequency on the MAX861CSA?

The FC pin on the MAX861CSA selects one of three nominal switching frequencies: FC = VDD or open → 13kHz; FC = GND → 100kHz; FC = OUT → 250kHz. These values are device-specific - the MAX861CSA differs from the MAX860CSA (6/50/130kHz). The oscillator and charge-pump frequencies are identical (no internal division), and frequency choice directly impacts capacitor sizing, supply current, and noise spectrum placement. For instance, 250kHz allows use of 2.2µF flying capacitors instead of 47µF at 13kHz.

Can the MAX861CSA replace the ICL7660 in an existing design?

Yes, the MAX861CSA can replace the ICL7660 in most SO-8 socketed designs with minimal modification: pin-for-pin compatible except that the ICL7660's OSC pin maps to the MAX861CSA's FC pin, and the ICL7660's unused pin 7 (NC) maps to the MAX861CSA's SHDN pin, which must be tied to VDD for permanent enable. No changes to C1/C2 values are needed, though higher MAX861CSA frequencies may allow smaller capacitors. Efficiency improves from ~70% (ICL7660) to 87%, and output current rises from 10mA to 50mA.

What is the role of the LV pin on the MAX861CSA?

The LV pin on the MAX861CSA determines operating mode: LV = GND configures the device as a voltage inverter (VOUT ≈ −VDD); LV = OUT configures it as a voltage doubler (VOUT ≈ +2×VDD). LV must not be left floating - in inverter mode, grounding LV ensures correct internal switch timing; in doubler mode, connecting LV to OUT enables the proper charge-transfer sequence. Incorrect LV connection causes malfunction or failure to start, and compatibility with MAX660/MAX665 requires LV reconnection per mode.

Does the MAX861CSA require external components to operate?

Yes, the MAX861CSA requires two external capacitors: C1 (flying capacitor) and C2 (output reservoir capacitor). Typical values are 10µF each for general-purpose use, though Table 3 in the datasheet recommends 4.7µF at 100kHz and 2.2µF at 250kHz. Low-ESR types (e.g., tantalum or ceramic) are mandatory - aluminum electrolytics must have ESR <0.2Ω. A 0.1µF bypass capacitor on VDD is also recommended when loading from VDD to OUT, while larger (≥10µF) bypassing is advised for VDD-to-GND loads to suppress supply ripple.