Analog Devices Inc. LTC694CS8-3.3#PBF

Overview

LTC694CS8-3.3#PBF from Analog Devices (formerly Linear Technology) is a 3.3V microprocessor supervisory circuit integrating power-on reset, battery back-up switching, RAM write protection, power-fail warning, and watchdog timing in an 8-pin SOIC package. It asserts RESET below 2.90V threshold, maintains logic-low RESET down to VCC = 1V, delivers up to 50mA from VOUT via charge-pumped NMOS switch, and draws only 0.6mW typical operating power - enabling robust system monitoring in space-constrained 3.3V embedded controllers and battery-backed memory systems.

For engineers reviewing the LTC694CS8-3.3#PBF datasheet, LTC694CS8-3.3#PBF pinout, LTC694CS8-3.3#PBF application, or LTC694CS8-3.3#PBF equivalent, key selection criteria include guaranteed reset assertion at 1V supply, 2.90V precision voltage monitor with 40mV hysteresis, 200μA typical supply current, fast 30ns CE IN-to-CE OUT propagation delay for RAM write gating, and compatibility with 3.3V-only systems requiring minimal external components.

Technical Context

The LTC694CS8-3.3#PBF implements dual comparator-based supervision: C1 monitors VCC against a 2.90V bandgap reference with 40mV hysteresis to generate RESET/LOW_LINE, while C3 compares PFI to a 1.3V internal reference for programmable power-fail detection. Its charge-pumped NMOS VOUT switch enables low-dropout (VCC – VOUT ≤ 0.1V at 1mA), low-quiescent-current operation, and seamless switchover to VBATT when VCC falls 50mV below VBATT.

Watchdog functionality uses an internal oscillator (100ms/1.6s timeout periods) or external clock input (OSC IN) with WDI transition detection; CE IN/CE OUT provides hardware-level RAM write protection by forcing CE OUT high during brownout. The device operates over 0°C to 70°C and features thermal limiting with shutdown at ~155°C.

Key Specifications

Pinout & Package

Package: 8-Lead Plastic SO (S8), RoHS-compliant, JEDEC MS-012AC, 3.9mm × 4.9mm body, 1.27mm pitch.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6326US33D3+ and TPS3808G33DBVR, the LTC694CS8-3.3#PBF uniquely integrates VOUT power switching, CE-based RAM write protection, and PFI/PFO early-warning capability in one 8-pin SOIC - eliminating four discrete components and reducing design risk in safety-critical 3.3V systems.

Availability

LTC694CS8-3.3#PBF is available at Aetrix Electronics and suitable for industrial PLC controllers, medical patient monitors, automotive telematics units, and smart energy meters requiring stable component supply with long-term lifecycle assurance.

Supply support for LTC694CS8-3.3#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. (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors for precision instrumentation, industrial automation, and power management.

The LTC694-3.3 family was designed specifically for 3.3V microprocessor systems needing integrated power supervision, battery backup, and memory protection - addressing reliability gaps in legacy 5V supervisors adapted for lower-voltage domains.

FAQ

What is the guaranteed minimum VCC level at which LTC694CS8-3.3#PBF asserts RESET?

The LTC694CS8-3.3#PBF guarantees RESET remains logic-low down to VCC = 1V, ensuring microprocessor reset integrity even during deep brownout conditions where other supervisors fail. This specification is tested and guaranteed over the full 0°C to 70°C operating temperature range, enabling robust operation in automotive and industrial environments with wide supply variation.

Does LTC694CS8-3.3#PBF support battery-backed RAM write protection?

Yes, the LTC694CS8-3.3#PBF provides hardware-level RAM write protection through its CE IN and CE OUT pins. When VCC falls below 2.90V or VBATT, CE OUT is forced high independently of CE IN, blocking write operations to CMOS RAM. This feature is implemented with a 30ns typical propagation delay, ensuring real-time protection without software overhead or timing uncertainty.

Can LTC694CS8-3.3#PBF monitor both main supply and backup battery voltage simultaneously?

No - the LTC694CS8-3.3#PBF monitors VCC (main 3.3V supply) with its internal 2.90V comparator and VBATT (backup battery) only for switchover control. It does not provide direct battery voltage measurement. However, the PFI input can be configured with an external resistor divider to monitor battery voltage indirectly, generating a PFO interrupt when battery voltage drops below a user-defined threshold relative to the 1.3V internal reference.

What is the maximum load current supported by the VOUT pin of LTC694CS8-3.3#PBF?

The VOUT pin of LTC694CS8-3.3#PBF supports up to 50mA continuous output current when powered from VCC via its internal charge-pumped NMOS switch. At 1mA load, dropout is typically VCC − 0.1V; at 50mA, dropout increases to VCC − 0.8V. For loads exceeding 50mA, external circuitry (e.g., Schottky diode from VCC to VOUT) is required, as the LTC694CS8-3.3#PBF lacks the BATT ON output found on the 16-pin LTC695 variant.

How does the watchdog timer in LTC694CS8-3.3#PBF operate without external components?

The LTC694CS8-3.3#PBF incorporates an internal oscillator that generates two fixed watchdog timeout periods: 100ms (short) and 1.6s (long), selected via the OSC SEL pin. No external capacitor or clock source is needed - toggling WDI within the selected timeout period prevents RESET assertion. If WDI remains static (high or low) beyond the timeout, both RESET and WDO go low, forcing system reset. Floating WDI disables the watchdog entirely.