Analog Devices Inc. LTC690MJ8

Overview

LTC690MJ8 from Analog Devices (formerly Linear Technology) is an 8-pin microprocessor supervisory IC providing guaranteed reset assertion down to VCC = 1V, 4.65V precision power supply monitoring, battery backup switching, power-fail warning, and watchdog timing. It integrates NMOS/PMOS switchover for CMOS RAM backup, delivers up to 50mA from VOUT, and supports 35ms minimum reset pulse width - used in embedded controllers requiring fail-safe power sequencing and nonvolatile memory protection.

For engineers reviewing the LTC690MJ8 datasheet, LTC690MJ8 pinout, LTC690MJ8 application, or LTC690MJ8 equivalent, this page delivers verified functional identity, confirmed pin roles (including RESET, VBATT, PFI, WDI), exact voltage thresholds (4.65V ±50mV), battery switchover hysteresis (20mV), and real-world use cases in automotive ECUs and battery-powered instrumentation.

Technical Context

The LTC690MJ8 implements a bandgap-referenced comparator (C1) with 40mV hysteresis to monitor VCC against a 4.65V threshold, ensuring glitch immunity during transient load events. Its internal charge-pump NMOS switch (M1) provides low-dropout VOUT regulation (5Ω typical R_DS(on)) during main power operation, while a PMOS switch (M2) enables battery backup with 125Ω effective resistance and ≤1µA standby current.

Watchdog timeout is configurable via OSC SEL: internal oscillator yields 1.6s long or 100ms short period (typical), with reset pulse generation triggered on WDI stall or VCC undervoltage. Power-fail detection uses a dedicated 1.3V reference comparator (C3) with <2µs response time and no built-in hysteresis - external resistor networks enable user-defined trip points.

Key Specifications

Pinout & Package

Package: 8-lead CERDIP (J8), hermetically sealed ceramic dual in-line package rated for –40°C to 85°C operation, with θ_JA = 130°C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX690ACPE+ and TPS3823DBVR, the LTC690MJ8 uniquely integrates battery switchover, power-fail warning, and watchdog timer in a single 8-pin CERDIP package - eliminating four external components while supporting full fail-safe sequencing in mission-critical embedded systems.

Availability

LTC690MJ8 is available at Aetrix Electronics and suitable for automotive engine control units, industrial programmable logic controllers, portable medical instrumentation, and smart meter data loggers requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LTC690MJ8 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 acquired Linear Technology in 2017 and maintains its legacy precision analog product lines, including supervisory ICs designed for high-reliability industrial and automotive applications.

The LTC690 family was engineered specifically for microprocessor systems needing coordinated reset, battery backup, power-fail warning, and watchdog functions - targeting applications where data integrity and deterministic power sequencing are non-negotiable.

FAQ

What is the guaranteed minimum VCC level at which LTC690MJ8 asserts RESET?

The LTC690MJ8 guarantees RESET remains logic low down to VCC = 1V with ISINK = 10µA, ensuring microprocessor hold in valid reset state during deep brownout. This specification is tested and guaranteed across the full –40°C to 85°C operating range, making LTC690MJ8 suitable for automotive and industrial environments with unstable power rails.

How does LTC690MJ8 handle battery switchover between VCC and VBATT?

LTC690MJ8 uses comparator C2 to monitor VCC–VBATT differential: it connects VOUT to VCC when VCC exceeds VBATT by ≥70mV (power-up), and switches to VBATT when VCC falls ≤50mV below VBATT (power-down), with 20mV hysteresis. The NMOS switch (M1) delivers up to 50mA from VCC; the PMOS switch (M2) supplies standby current ≤1µA from VBATT - all implemented internally in LTC690MJ8.

Can LTC690MJ8 generate a power-fail interrupt before RESET assertion?

Yes. LTC690MJ8 provides dedicated PFI and PFO pins: PFI accepts a voltage divider from the monitored supply, and PFO asserts low when PFI falls below the internal 1.3V reference - typically configured to trigger 5–10ms before VCC reaches the 4.65V reset threshold. This gives the microprocessor time to execute shutdown routines before RESET forces hardware reset.

What is the function of the WDI pin on LTC690MJ8 and how is it timed?

The WDI (Watchdog Input) pin on LTC690MJ8 resets the internal watchdog timer on every high-to-low or low-to-high transition. If WDI remains static longer than the selected timeout (100ms short or 1.6s long, set by OSC SEL), LTC690MJ8 forces RESET and WDO low. Floating WDI disables the watchdog. Minimum pulse width is 200ns, and timing is derived from the internal oscillator - no external clock required for basic operation.

Does LTC690MJ8 require external components for basic reset functionality?

No. LTC690MJ8 operates as a complete supervisory solution with only two mandatory external components: a 0.1µF bypass capacitor on VCC and another on VOUT. All core functions - reset generation, battery switchover, power-fail detection, and watchdog timing - are self-contained. External resistors are optional only for PFI voltage division or hysteresis enhancement, not for baseline operation.