Analog Devices Inc. LTC694IN8-3.3#PBF

Overview

LTC694IN8-3.3#PBF from Analog Devices (formerly Linear Technology) is an 8-pin PDIP-packaged 3.3V microprocessor supervisory circuit with integrated battery backup switchover, RAM write protection, power-fail warning, and watchdog timing. It asserts reset down to VCC = 1V, monitors supply at 2.90V threshold, delivers up to 50mA from VOUT via charge-pumped NMOS switch, and consumes only 0.6mW typical operating power - enabling reliable power management in battery-backed embedded controllers.

For engineers reviewing the LTC694IN8-3.3#PBF datasheet, LTC694IN8-3.3#PBF pinout, LTC694IN8-3.3#PBF application, or LTC694IN8-3.3#PBF equivalent, key selection criteria include guaranteed reset assertion below 1V, 2.90V precision voltage monitoring, fast 30ns CE gating, 1μA max battery-backup current, and compatibility with industrial temperature range (–40°C to +85°C) designs requiring long-term data retention and fail-safe shutdown.

Technical Context

The LTC694IN8-3.3#PBF integrates five core functions in a single IC: a precision 2.90V reset comparator with 40mV hysteresis, a charge-pumped NMOS VOUT switch (5Ω typical R_DS(on), 50mA max), a PMOS battery switchover path (20mV hysteresis, 50mV switchover threshold), a 1.3V-referenced power-fail comparator (PFI/PFO), and a dual-mode watchdog timer (internal oscillator or external clock input). All functions operate across –40°C to +85°C with full specification.

It implements conditional battery backup: when VCC drops below VBATT by ≥50mV, VOUT automatically switches to VBATT through a low-dropout PMOS switch; during normal operation, VOUT is sourced from VCC via a low-quiescent-current NMOS switch. The RESET output remains valid down to VCC = 1V, and CE IN/CE OUT provide hardware-enforced RAM write protection with 30ns propagation delay.

Key Specifications

Pinout & Package

Package: 8-lead PDIP (N8), body size 0.300" × 0.400", lead pitch 0.100", JEDEC MS-001-AB compliant. RoHS-compliant lead-free finish (#PBF).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX691ACPE+ and TPS3808G33DBVR, the LTC694IN8-3.3#PBF uniquely integrates battery switchover, RAM write protection, and programmable power-fail warning in an industrial-temp 8-pin PDIP - making it irreplaceable for data-critical, battery-backed embedded systems requiring full supervision functionality.

Availability

LTC694IN8-3.3#PBF is available at Aetrix Electronics and suitable for industrial data loggers, automotive telematics units, medical portable monitors, and smart utility meters requiring stable component supply across extended temperature ranges and long product lifecycles.

Supply support for LTC694IN8-3.3#PBF 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

Analog Devices, Inc. (ADI) is a global semiconductor leader specializing in high-performance analog, mixed-signal, and digital signal processing technologies for precision instrumentation, industrial automation, and mission-critical systems.

The LTC694-3.3 family was designed specifically for robust 3.3V microprocessor supervision in harsh environments - delivering guaranteed reset down to 1V, ultra-low battery-backup current, and integrated memory protection without external components.

FAQ

What is the guaranteed minimum VCC level at which LTC694IN8-3.3#PBF asserts RESET?

The LTC694IN8-3.3#PBF guarantees RESET remains active low down to VCC = 1V with ISINK = 10μA, ensuring microprocessor hold-down during severe brownout conditions. This specification is fully tested over the –40°C to +85°C industrial temperature range and is independent of VBATT voltage. The internal reset comparator and output driver maintain logic integrity even as VCC collapses, preventing spurious release that could cause system instability. This capability is explicitly documented in the Absolute Maximum Ratings and Electrical Characteristics tables of the LTC694-3.3/LTC695-3.3 datasheet.

Does LTC694IN8-3.3#PBF support battery-backed RAM write protection, and how is it implemented?

Yes, the LTC694IN8-3.3#PBF supports hardware-enforced RAM write protection via its CE IN and CE OUT pins. When VCC falls below the 2.90V reset threshold or VBATT, CE OUT is forced high regardless of CE IN state - disabling chip enable to CMOS RAM and preventing writes during invalid supply conditions. This function operates with 30ns typical propagation delay and is fully specified over temperature. Unlike software-based protection, this hardware gating ensures deterministic behavior during transients. The LTC694IN8-3.3#PBF implements this using internal comparators and logic, requiring no external components beyond standard decoupling capacitors.

What is the maximum continuous output current capability of the VOUT pin on LTC694IN8-3.3#PBF?

The VOUT pin on the LTC694IN8-3.3#PBF delivers up to 50mA continuously when powered from VCC via its internal charge-pumped NMOS switch, with a typical on-resistance of 5Ω. This rating applies across the full –40°C to +85°C operating range and includes short-circuit protection. In battery backup mode (VCC < VBATT), VOUT is sourced from VBATT through a PMOS switch rated for lower current but optimized for ultra-low dropout and 1μA max standby draw. The 50mA capability eliminates need for external regulators in most SRAM and low-power logic applications, as confirmed in the Electrical Characteristics table under "VOUT Output Voltage" and "VOUT Output Current" parameters.

Can LTC694IN8-3.3#PBF generate an early warning signal before system reset occurs?

Yes, the LTC694IN8-3.3#PBF provides early power-fail warning via its PFI/PFO interface. By connecting PFI to a resistor divider from the 3.3V rail (e.g., 51kΩ/16kΩ), the internal 1.3V comparator triggers PFO low when input voltage drops below ~1.3V - typically 10–15ms before VCC reaches the 2.90V reset threshold. This allows the microprocessor to execute controlled shutdown, save critical data, or enter low-power mode. The PFI comparator has no built-in hysteresis, but external hysteresis can be added using a feedback resistor from PFO to PFI, as detailed in the Applications Information section. This feature is unique to the LTC694-3.3/LTC695-3.3 family and not present in basic reset supervisors.

What is the operating temperature range qualification for LTC694IN8-3.3#PBF?

The LTC694IN8-3.3#PBF is qualified for industrial operation from –40°C to +85°C, as indicated by the "I" suffix in the part number and confirmed in the Order Information table. All electrical specifications - including reset threshold (2.90V ±0.1V), supply current (0.6mW typical), battery backup current (1μA max), and CE propagation delay (30ns) - are guaranteed across this full range. Thermal shutdown activates at ~155°C with 10°C hysteresis to prevent oscillation. This qualification makes the LTC694IN8-3.3#PBF suitable for under-hood automotive, factory-floor industrial, and outdoor infrastructure applications where ambient temperatures exceed commercial-grade limits.