Analog Devices Inc./Maxim Integrated MAX805LCPA

Overview

The MAX805LCPA from Maxim Integrated is a microprocessor supervisory circuit providing active-high reset, battery-backup switchover, watchdog timer, and power-fail detection for +5V systems. It asserts RESET when VCC drops below 4.65V, delivers 200ms reset pulse width, consumes 200µA supply current, and supports VBATT switchover with 40mV hysteresis. It is used in battery-powered controllers to maintain CMOS RAM integrity during brownout.

For engineers reviewing the MAX805LCPA datasheet, MAX805LCPA pinout, MAX805LCPA application, or MAX805LCPA equivalent, key selection criteria include its guaranteed active-high RESET assertion down to VCC = 1.1V, 1.25V PFI threshold accuracy, ±2% power-fail comparator tolerance (shared with MAX802L), and compatibility with Intel 80C51-style µPs requiring high-true reset signaling.

Technical Context

The MAX805LCPA integrates four independent functional blocks: a precision voltage monitor with 4.65V reset threshold and 40mV hysteresis; a 1.6s watchdog timer cleared by WDI edges; a 1.25V reference-based power-fail comparator driving PFO; and a dual-path battery switchover circuit routing VOUT to VCC or VBATT based on voltage comparison and reset state. All logic is internally synchronized to avoid metastability during transitions.

Its active-high RESET output differs from the MAX690A/MAX802L's active-low variant, enabling direct interface with µPs like the 80C51 without external inverters. The device guarantees RESET validity down to VCC = 1.1V and maintains <1µA quiescent current in full battery-backup mode when VCC < VBATT − 1V.

Key Specifications

Pinout & Package

MAX805LCPA is housed in an 8-pin plastic DIP package (0.300" wide) with standard through-hole footprint and RoHS-compliant lead finish. Pin 1 is VBATT, pin 2 is VCC, pin 3 is GND, pin 4 is PFI, pin 5 is PFO, pin 6 is WDI, pin 7 is RESET (active-high), and pin 8 is VOUT.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar microprocessor supervisory applications.

Compared with MAX802LCPA and MAX813LCPA, the MAX805LCPA uniquely delivers guaranteed active-high RESET down to VCC = 1.1V without external components-critical for 80C51-family µPs-and eliminates the need for MR or WDEN pins in fixed-function embedded monitors.

Availability

MAX805LCPA is available at Aetrix Electronics and suitable for battery-powered controllers, intelligent instrumentation, critical µP power monitoring, embedded data acquisition systems, and industrial telemetry requiring stable component supply across extended product lifecycles.

Supply support for MAX805LCPA 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 mixed-signal ICs for industrial, automotive, communications, and computing markets, with emphasis on reliability and integration.

The MAX805LCPA belongs to Maxim's microprocessor supervisory product line, engineered specifically for robust power-monitoring and battery-switchover in mission-critical embedded systems operating from +5V rails.

FAQ

What is the guaranteed minimum VCC level at which MAX805LCPA asserts RESET?

The MAX805LCPA guarantees active-high RESET assertion down to VCC = 1.1V across the 0°C to +70°C operating range. This specification ensures reliable reset signaling even during deep brownout conditions where other supervisory ICs may lose output drive capability. The MAX805LCPA maintains this guarantee while delivering full logic-level output swing referenced to the higher of VCC or VBATT, making it suitable for µPs like the Intel 80C51 that require high-true reset inputs.

How does the MAX805LCPA handle battery switchover hysteresis?

The MAX805LCPA implements 40mV hysteresis between VCC and VBATT for switchover: VBATT connects to VOUT when VCC falls 20mV below VBATT, and VCC reconnects to VOUT when it rises 20mV above VBATT. This prevents oscillatory switching during slow VCC decay, ensuring stable RAM supply. The hysteresis is built into the internal comparator and requires no external components-unlike solutions needing discrete Schmitt triggers or RC networks.

Can the MAX805LCPA monitor power supplies other than +5V?

Yes, the MAX805LCPA can monitor non-+5V supplies using its PFI input and internal 1.25V reference. By connecting a resistor divider from the target supply to PFI, users scale the monitored voltage so that the divider output equals 1.25V at the desired trip point-for example, a 12V supply failing at 10.8V would use R1/R2 = 7.6. The PFI input draws only ±25nA, minimizing divider error and enabling high-impedance sensing.

What is the maximum allowable VBATT voltage for MAX805LCPA?

The maximum allowable VBATT voltage for the MAX805LCPA is 4.80V, as specified in Maxim's Application Note and Table 2 of the datasheet. Exceeding this voltage risks forward-biasing the internal substrate diode (D1) when VCC is near its reset threshold, causing unintended current flow from VBATT to VCC. Lithium cells (3.0–3.6V) and properly sized supercapacitors remain within safe operating limits.

Does the MAX805LCPA require external components for basic reset functionality?

No, the MAX805LCPA requires no external components for core reset functionality: its 4.65V threshold, 200ms pulse width, and active-high RESET output are fully internal. External components are optional-e.g., a pull-up resistor on WDI to disable watchdog, or a voltage divider on PFI for custom power-fail thresholds. This reduces BOM cost and PCB area versus discrete reset solutions.