Analog Devices Inc. LTC694IS8-3.3#TRPBF

Overview

LTC694IS8-3.3#TRPBF 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. It is used in battery-backed embedded controllers requiring guaranteed low-voltage reset assertion and seamless switchover to auxiliary power.

For engineers reviewing the LTC694IS8-3.3#TRPBF datasheet, LTC694IS8-3.3#TRPBF pinout, LTC694IS8-3.3#TRPBF application, or LTC694IS8-3.3#TRPBF equivalent, key selection criteria include guaranteed reset assertion at VCC = 1V, 2.90V precision voltage monitor with 40mV hysteresis, 200μA typical supply current, fast 30ns CE IN-to-CE OUT propagation delay, and thermal limiting for safe-area operation under overload.

Technical Context

The LTC694IS8-3.3#TRPBF implements three independent comparators: C1 monitors VCC against a 2.90V bandgap reference for reset generation with 40mV hysteresis; C2 compares VCC and VBATT to control NMOS/PMOS power switches for automatic switchover with 70mV/50mV thresholds and 20mV hysteresis; C3 compares PFI against a 1.3V internal reference for power-fail detection without hysteresis. All comparators operate across –40°C to +85°C.

It integrates a programmable watchdog timer with two timeout periods (100ms/1.6s typical) selectable via OSC SEL, and a gated chip-enable output (CE OUT) that forces high during reset to protect RAM writes. The device uses internal charge-pump circuitry to drive the NMOS VOUT switch, achieving low dropout (VCC – VOUT ≤ 0.1V at 1mA) and eliminating substrate injection current into VBATT - critical for lithium battery safety.

Key Specifications

Pinout & Package

Package: 8-lead plastic SOIC (S8), JEDEC MS-012AC, 3.9mm × 4.9mm body, 1.27mm pitch, thermal resistance θ_JA = 180°C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6326US31D3+ and TPS3808G33DBVR, the LTC694IS8-3.3#TRPBF uniquely integrates battery switchover, RAM write protection, and power-fail warning in a single 8-pin SOIC - eliminating external components and PCB area while enabling robust data retention in brownout conditions.

Availability

LTC694IS8-3.3#TRPBF is available at Aetrix Electronics and suitable for industrial PLCs, medical handhelds, automotive BCMs, and smart energy meters requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LTC694IS8-3.3#TRPBF 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 reliability-critical systems.

The LTC694-3.3 product line was designed specifically for 3.3V microprocessor systems needing integrated power supervision, battery-backed memory management, and fail-safe watchdog timing - with emphasis on low power, wide temperature operation, and lithium-battery-safe architecture.

FAQ

What is the guaranteed minimum VCC level at which LTC694IS8-3.3#TRPBF asserts RESET?

The LTC694IS8-3.3#TRPBF guarantees RESET remains logic-low down to VCC = 1V, ensuring reliable microprocessor hold-down during deep brownout events. This specification is tested and guaranteed over the full –40°C to +85°C operating temperature range, enabling robust operation in harsh environments where supply rails may sag significantly before complete failure.

Does LTC694IS8-3.3#TRPBF support battery switchover, and what are the thresholds?

Yes, the LTC694IS8-3.3#TRPBF supports automatic battery switchover between VCC and VBATT. It connects VOUT to VCC when VCC exceeds VBATT by 70mV (power-up threshold) and switches to VBATT when VCC falls within 50mV of VBATT (power-down threshold), with 20mV hysteresis to prevent chatter. This enables seamless transition to backup power without external circuitry.

How does LTC694IS8-3.3#TRPBF protect RAM during power failure?

The LTC694IS8-3.3#TRPBF protects RAM using dual mechanisms: first, it forces CE OUT high whenever VCC drops below 2.90V or VBATT, disabling chip enable signals to prevent writes; second, its 30ns typical CE IN-to-CE OUT propagation delay ensures near-instantaneous gating. This preserves data integrity in CMOS RAM, EEPROM, and NOVRAM during supply instability.

What is the purpose of the PFI and PFO pins on LTC694IS8-3.3#TRPBF?

The PFI (Power-Fail Input) pin accepts a divided-down version of the main supply to feed comparator C3, which references an internal 1.3V bandgap. When PFI falls below 1.3V, the PFO (Power-Fail Output) pin goes low - providing an early warning interrupt to the microprocessor 10–15ms before RESET activates, allowing time for controlled data save and system shutdown.

Can LTC694IS8-3.3#TRPBF drive external circuitry beyond its 50mA VOUT limit?

No - the LTC694IS8-3.3#TRPBF's VOUT is rated for 50mA maximum due to its internal NMOS switch. For higher currents, use the LTC695-3.3 variant which provides a BATT ON output to drive an external PNP transistor. Attempting to exceed 50mA on LTC694IS8-3.3#TRPBF triggers thermal shutdown at ~155°C, protecting the device but disrupting operation.