Analog Devices Inc./Maxim Integrated MAX813LCUA+

Overview

MAX813LCUA+ from Maxim Integrated is a low-cost microprocessor supervisory circuit providing active-high reset output, watchdog timer, power-fail comparator, and manual-reset input in an 8-pin µMAX package. It asserts RESET when VCC drops below 4.65V, monitors external supplies via PFI (1.25V threshold), and delivers a guaranteed 200ms reset pulse width - used in embedded controllers and industrial instrumentation for reliable power-up/down sequencing.

For engineers reviewing the MAX813LCUA+ datasheet, MAX813LCUA+ pinout, MAX813LCUA+ application, or MAX813LCUA+ equivalent, key selection criteria include its 4.65V reset threshold, 1.6s watchdog timeout, guaranteed RESET validity down to VCC = 1.1V, and compatibility with TTL/CMOS logic interfaces in space-constrained designs.

Technical Context

The MAX813LCUA+ integrates four core supervisory functions: a precision voltage monitor with 4.65V ±1.5% reset threshold and 40mV hysteresis; a watchdog timer that triggers WDO low after 1.6s of no WDI edge transition; a 1.25V reference-based power-fail comparator (PFI/PFO); and a debounced active-low manual-reset input (MR) with 250µA internal pull-up.

Its RESET output is active-high and valid down to VCC = 1.1V, while WDO provides independent watchdog status. Unlike MAX705/MAX706, it omits active-low RESET but retains full watchdog functionality - making it suitable for µPs requiring active-high reset (e.g., Intel 80C51) without redundant reset polarity support.

Key Specifications

Pinout & Package

MAX813LCUA+ is housed in an 8-pin µMAX package (package code U8+1, outline 21-0036), measuring 3.0mm × 3.0mm × 0.8mm with exposed pad for thermal enhancement. The package is RoHS-compliant and lead(Pb)-free, indicated by the '+' suffix.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX705CUA+, MAX813LCUA+ eliminates need for external inverters in active-high reset systems; versus TPS3808G125DBVR, it integrates watchdog and power-fail comparator - reducing component count and PCB area in complex embedded controllers.

Availability

MAX813LCUA+ is available at Aetrix Electronics and suitable for industrial control systems, medical instrumentation, automotive body electronics, and smart metering applications requiring stable component supply and long-term lifecycle support.

Supply support for MAX813LCUA+ 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 semiconductor company specializing in analog and mixed-signal ICs for power, sensing, connectivity, and security applications.

The MAX813L family was designed specifically for cost-sensitive microprocessor supervisory needs in industrial and embedded systems - integrating reset, watchdog, and power-fail monitoring in minimal footprint without sacrificing accuracy or reliability.

FAQ

What is the reset threshold voltage for MAX813LCUA+ and how tightly is it specified?

The MAX813LCUA+ has a nominal reset threshold of 4.65V with a tolerance of ±1.5%, meaning the actual trip point falls between 4.58V and 4.72V over temperature and supply variations. This specification is guaranteed across the full operating range (0°C to +70°C) and ensures consistent reset behavior in +5V systems before brownout affects microprocessor stability. The MAX813LCUA+ uses an internal bandgap reference to maintain this accuracy without external calibration.

Can MAX813LCUA+ monitor a 3.3V supply, and if so, how?

Yes, MAX813LCUA+ can monitor a 3.3V supply using its PFI input and internal 1.25V comparator reference. Connect the 3.3V rail to PFI through a resistor divider (e.g., 100kΩ top, 62kΩ bottom) to scale it to ~1.25V. When the 3.3V rail drops below ~3.25V, PFI falls below 1.25V and PFO goes low - triggering an interrupt or initiating shutdown. The MAX813LCUA+ datasheet confirms PFI input current is ±25nA, ensuring minimal loading on the divider network.

Does MAX813LCUA+ provide both active-high and active-low reset outputs?

No, MAX813LCUA+ provides only an active-high RESET output. Unlike the MAX707/MAX708, it does not include a complementary active-low RESET pin. The MAX813LCUA+ is functionally identical to MAX705 except for substituting RESET for RESET - making it ideal for microprocessors requiring active-high reset (e.g., Intel 80C51) without redundant output polarity. Its WDO pin remains active-low and separate.

What is the minimum VCC required for MAX813LCUA+ to assert a valid RESET output?

The MAX813LCUA+ guarantees valid RESET output down to VCC = 1.1V, as confirmed in the Electrical Characteristics table under "RESET Output Voltage" test condition (MAX813LC, ISOURCE = 4μA, VCC = 1.1V). At this voltage, RESET remains a strong logic high (>0.8V), enabling reliable reset assertion during battery backup or deep brownout scenarios - a key differentiator from competitors with higher minimum VCC requirements.

How does the watchdog timer in MAX813LCUA+ get cleared, and what triggers a timeout?

The MAX813LCUA+ watchdog timer clears on any rising or falling edge at WDI, when RESET is asserted, or when WDI is three-stated (high-impedance). A timeout occurs if WDI remains static (high or low) for 1.6 seconds ±40%, causing WDO to go low. Pulses as short as 50ns are detected, allowing robust firmware servicing even during tight interrupt latency windows. The MAX813LCUA+ datasheet specifies tWD = 1.00–2.25s under full temperature and voltage range.