Analog Devices Inc. ADM690AN

ADM690AN Product Summary

The ADM690AN from Analog Devices Inc. is a robust single-channel supervisory integrated circuit, engineered specifically for microprocessor systems requiring reliable power monitoring, reset control, and data retention during power interruptions. Packaged in an industry-standard 8-pin DIP, the ADM690AN integrates key monitoring and backup functions, minimizing the IC count in designs and delivering essential reliability in mission-critical applications. Part of the ADM690–ADM695 supervisory family, this device is deployed extensively in computers, controllers, intelligent instruments, and automotive electronics to ensure safe operation and preserve system integrity during transient and sustained power events.

Essential Operating Characteristics of the ADM690AN

The ADM690AN excels in providing comprehensive microprocessor supervision capabilities. Key functional highlights include:

Superior low-voltage monitoring, with reset assertion guaranteed down to V_CC as low as 1 V, ensuring systems are held in a safe state even during severe brownouts.

Precision voltage detection that triggers reset outputs when supply voltages fall outside preset thresholds, supporting nominal 5 V systems (reset threshold typically at 4.65 V).

Push-pull, totem pole reset outputs for standard logic compatibility, with a 50 ms reset pulse width after voltage recovery to accommodate microprocessor clock stabilization.

A watchdog timer that outputs a RESET pulse if it is not toggled within 1.6 seconds, protecting against software lockup and system stalls. The watchdog can be disabled simply by leaving WDI unconnected.

Integrated automatic battery backup switching between a primary supply (V_CC) and a backup battery (V_BATT), with extremely fast gating and low switch-on-resistance (1.5 Ω normal, 20 Ω backup path).

Standby currents as low as 600 nA to conserve battery energy during backup.

High current drive capability up to 100 mA at the V_OUT terminal, supporting memory banks and other peripherals requiring seamless power transitions.

Dedicated power-fail comparator, with a 1.3 V precision reference for monitoring secondary supply rails or battery levels, providing critical early warnings before an impending power loss.

ADM690AN Pin Descriptions and Package Details

Housed in an 8-pin DIP, the ADM690AN’s pinout is optimized for microprocessor monitoring roles:

V_CC: Main system supply input.

V_BATT: Backup battery input, facilitating automatic switchover for memory retention.

V_OUT: Output to the system RAM or critical circuit, switched between V_CC and V_BATT.

GND: Ground reference.

RESET: Active-low reset output, acting as the primary microprocessor reset signal.

WDI: Watchdog input pin, monitored for activity to guard against processor malfunctions.

PFI: Power fail input for auxiliary supply or line monitoring.

PFO: Power fail output, signaling to the system when monitored voltage falls below threshold.

The DIP-8 format allows easy integration in both through-hole prototyping and mature PCB production flows, accommodating direct replacement scenarios or straightforward new designs.

ADM690AN Electrical and Environmental Parameters

The ADM690AN is engineered for demanding operational environments:

Absolute maximum supply voltages: V_CC and V_BATT each rated from -0.3 V to +6 V.

Operating temperature range (Industrial A version): -40°C to +85°C, supporting deployment in industrial and automotive settings.

Power dissipation: 400 mW for 8-pin DIP, with thermal impedance of 120°C/W, ensuring stable performance under typical load conditions.

Input currents: Main supply up to 200 mA; battery backup input supports up to 50 mA, aligning with typical lithium coin cell and capacitor-based designs.

Digital outputs and logic: Drive currents rated at 20 mA (per output).

ESD tolerance: Advanced CMOS process and proprietary protection provide resilience, though standard ESD precautions must be observed.

Storage temperature: -65°C to +150°C, suitable for extended logistical and pre-installation storage cycles.

Battery Backup and Switching Mechanism of the ADM690AN

A defining strength of the ADM690AN is its seamless automatic battery switchover circuit. The device monitors the difference between V_CC and V_BATT and connects V_OUT to whichever is higher, switching with 20 mV hysteresis to prevent chatter during marginal conditions. An internal PMOS pass transistor (1.5 Ω typical on-resistance) is engaged when V_CC exceeds V_BATT; when primary supply drops below V_BATT, a MOSFET switch (20 Ω) connects the backup source, minimizing voltage drop for CMOS RAM and low-power logic.

Output current for V_OUT is rated at 100 mA, with advice to employ a 0.1 μF or larger capacitor locally at V_OUT to handle transient demands. The backup system is compatible with battery voltages from 2.0 V to 4.25 V, making it suitable for lithium cells, supercapacitors, or rechargeable options. The ADM690AN also features a small trickle charge current (10 nA typical, max 0.1 μA) for maintaining rechargeable backup cells.

For systems requiring higher current or lower voltage drop, an external PNP transistor can be added, further increasing output capacity by taking its drive signal from the ADM690AN family’s auxiliary output pins (in other package variants).

Power Failure Monitoring and Reset System in the ADM690AN

Ensuring that microprocessors never execute code with unreliable or slowly decaying supply voltages, the ADM690AN integrates a precision threshold detector and logic for multiple reset scenarios:

On power-down, if V_CC falls below the nominal 4.65 V threshold, a RESET output is asserted (held low) and persists down to V_CC as low as 1 V, securing the processor in a well-defined state.

Upon supply recovery, RESET remains low for a fixed interval (50 ms), allowing both the power source and microprocessor clock to stabilize before normal execution resumes.

The ADM690AN’s reset comparator is characterized by fast response (<1 μs) and about 50 mV hysteresis for noise immunity.

An auxiliary power-fail input (PFI) accepts an externally scaled supply or battery-derived voltage divider, compared to a 1.3 V internal reference. If PFI falls below this reference, the PFO output informs the processor an impending failure is expected, supporting preemptive housekeeping or data storage prior to full power loss.

ADM690AN Watchdog Timer Feature

System reliability is further bolstered by the ADM690AN’s integrated watchdog circuit:

Engineers can connect a microprocessor I/O line to the WDI pin, writing firmware to toggle this signal regularly (timeout fixed at 1.6 s).

If WDI does not transition within this window, the ADM690AN autonomously issues a RESET, bootstrapping the microprocessor back to a known state.

This mechanism protects against firmware stalls, infinite loops, or clock anomalies that risk keeping the microprocessor in an unresponsive state.

The watchdog can be readily disabled in systems where it is not required, or enabled/disabled under software control using external logic.

ADM691/ADM693/ADM695 variants offer adjustable watchdog timing via external capacitors or oscillators; for ADM690AN, the timing remains fixed for simplicity and predictability.

ADM690AN Typical Applications

The ADM690AN is widely used across microprocessor-based systems demanding secure data retention, clean power-up and power-down sequences, and autonomous fault detection. Key use cases include:

Computers and embedded controllers requiring protected RAM or EEPROM write operations during supply transitions.

Industrial or automotive systems needing to safeguard high-value data/logging through brief brownouts, switchovers to standby, or controlled shutdown upon detecting primary supply instability.

Intelligent instrumentation where early warning of power fail and automatic backup power engagement prevents data loss and system corruption.

Scenarios where engineering logic dictates that only a single IC oversees reset, voltage monitoring, battery switch, and watchdog tasks—minimizing PCB footprint, power consumption, and BOM complexity.

Alternative or Substitute Devices for the ADM690AN

For engineers and procurement personnel evaluating alternatives or complementary models, the ADM690AN belongs to a comprehensive family with related devices:

ADM691, ADM693, ADM695: Available in 16-pin DIP or SOIC, these add features such as RAM write protection, active high RESET outputs, adjustable reset and watchdog times, and additional status outputs (e.g., battery-on indication).

ADM692, ADM694: Other 8-pin DIP models with minor differences in voltage thresholds and reset timings, suitable for +5 V ±10% or +5 V +10%/–5% tolerance systems respectively.

Devices from the MAX690–MAX695 family (by Maxim Integrated) are considered compatible or baseline alternatives, but careful comparison of voltage thresholds, timing parameters, and package selections is essential for drop-in replacement.

Custom requirements (e.g., adjustable watchdog via capacitor, write buffering, specific output drive) should guide the choice among family variants or competitor equivalents.

Conclusion

on the ADM690AN’s selection value

The ADM690AN stands out as a fully integrated solution for safeguarding microprocessor-based systems from data corruption, improper code execution during power events, and loss of critical system state. Its precise supply monitoring, battery backup capability, low power footprint, and seamless interface with both modern and legacy microprocessor architectures make it a dependable selection for demanding embedded and industrial engineering projects. When selecting a supervisory IC for robust, fail-safe operation in harsh environments or data-sensitive platforms, the ADM690AN provides an optimal blend of technical capability, application-proven design, and straightforward integration.