Analog Devices Inc. LTC694IS8-3.3#PBF

Overview

LTC694IS8-3.3#PBF from Analog Devices (formerly Linear Technology) is an 8-pin SOIC supervisory IC for 3.3V microprocessor systems, providing guaranteed reset assertion down to VCC = 1V, 2.90V precision supply monitoring, battery-backed RAM power switching, and integrated watchdog timing. It delivers 50mA VOUT from VCC via charge-pumped NMOS switch (typ. 5Ω R_DS(on)) and switches to VBATT (1.5–2.75V) with 50mV switchover hysteresis for low-power CMOS RAM backup.

For engineers reviewing the LTC694IS8-3.3#PBF datasheet, LTC694IS8-3.3#PBF pinout, LTC694IS8-3.3#PBF application, or LTC694IS8-3.3#PBF equivalent, key selection criteria include guaranteed reset at 1V VCC, 1μA max battery-backup current, 30ns CE IN→CE OUT propagation delay, and compatibility with industrial temperature range (–40°C to +85°C).

Technical Context

The LTC694IS8-3.3#PBF integrates four functional blocks: a precision 2.90V reset comparator (C1) with 40mV hysteresis and 10ms response; a battery switchover circuit (C2) using NMOS/PMOS switches with 70mV/50mV thresholds and 20μs response; a 1.3V-referenced power-fail comparator (C3); and a dual-mode watchdog timer supporting internal oscillator (100ms/1.6s timeout) or external clock input. All logic outputs (RESET, RESET, PFO, WDO, LOW_LINE, BATT ON, CE OUT) are push-pull with defined sink/source specs.

It operates across –40°C to +85°C, draws 200μA typical supply current at 3.6V, and reduces to 1μA max in battery-backup mode (VCC = 0V, VBATT = 2V). The device implements thermal limiting (~155°C shutdown) and short-circuit protection on VOUT (200mA limit), with no substrate injection current-critical for lithium battery safety.

Key Specifications

Pinout & Package

Package: 8-lead plastic SO (S8), 1.27mm pitch, JEDEC MS-012AC, θ_JA = 180°C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6326US31D3+T and TPS3808G33DBVR, the LTC694IS8-3.3#PBF uniquely integrates reset, battery switchover, power-fail detection, watchdog, and CE gating in one 8-pin SOIC-reducing BOM count, PCB area, and validation effort for 3.3V industrial systems requiring full power supervision.

Availability

LTC694IS8-3.3#PBF is available at Aetrix Electronics and suitable for industrial PLC controllers, automotive telematics units, medical portable monitors, and smart energy meters requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LTC694IS8-3.3#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 leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, formed through the acquisition of Linear Technology in 2017.

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

FAQ

What is the guaranteed minimum VCC voltage at which LTC694IS8-3.3#PBF asserts RESET?

The LTC694IS8-3.3#PBF guarantees RESET remains logic-low down to VCC = 1V with ISINK = 10μA, ensuring microprocessor stability during deep brownout events. This specification is tested and guaranteed over the full –40°C to +85°C operating temperature range and is independent of VBATT voltage. The LTC694IS8-3.3#PBF achieves this via dedicated low-voltage biasing in its internal reset comparator and output driver stages.

Does LTC694IS8-3.3#PBF support battery-backed RAM power switching, and what are the voltage limits?

Yes, the LTC694IS8-3.3#PBF supports automatic battery-backed RAM power switching via its VOUT pin. It accepts VBATT input from 1.5V to 2.75V and switches VOUT from VCC to VBATT when VCC falls 50mV below VBATT. In battery-backup mode, VOUT delivers power with ≤1μA supply current and maintains regulation within VBATT − 0.1V (min) to VBATT − 0.02V (typ). The LTC694IS8-3.3#PBF uses a PMOS switch for this path, optimized for low dropout in standby CMOS RAM applications.

How does the watchdog timer on LTC694IS8-3.3#PBF operate, and can it be disabled?

The watchdog timer on the LTC694IS8-3.3#PBF is enabled by toggling the WDI pin and offers two timeout periods: 100ms (short) or 1.6s (long), selected via OSC SEL. It resets on every WDI transition and forces RESET and WDO low if no transition occurs within the timeout window. The timer is fully disabled when WDI is left floating-no external pull-up/down required. This behavior is guaranteed across temperature and supply voltage, and the LTC694IS8-3.3#PBF datasheet specifies ±20% timeout accuracy under nominal conditions.

What is the purpose of the CE IN and CE OUT pins on LTC694IS8-3.3#PBF, and how do they protect memory?

The CE IN and CE OUT pins on the LTC694IS8-3.3#PBF implement hardware write protection for battery-backed RAM. CE IN accepts a chip-enable signal from the microprocessor; CE OUT replicates it with 30ns typical delay when VCC is valid, but forces high (logic-inactive) whenever VCC falls below 2.90V or VBATT. This blocks write operations during power instability, preventing data corruption. The LTC694IS8-3.3#PBF's CE OUT drives CMOS RAM CE/CS inputs directly and is rated for 800μA sink current.

Can LTC694IS8-3.3#PBF monitor an external power rail for early failure warning, and how is it configured?

Yes, the LTC694IS8-3.3#PBF monitors external rails via the PFI pin, comparing it to an internal 1.3V reference. A resistor divider (e.g., 51kΩ/16kΩ from 5V input) sets the trip point-typically adjusted so PFO asserts 10–15ms before RESET activates. PFO is an active-low, push-pull output compatible with μP interrupt lines. Hysteresis can be added externally using feedback resistors, and the LTC694IS8-3.3#PBF's PFI input draws only ±25nA, minimizing divider loading error.