Analog Devices Inc. LTC690CS8#PBF

Overview

LTC690CS8#PBF from Analog Devices (formerly Linear Technology) is an 8-pin microprocessor supervisory IC integrating power-on reset, battery backup switching, power-fail warning, and watchdog timer functions. It features a 4.65V precision reset threshold, guaranteed RESET assertion down to VCC = 1V, 35ms minimum reset pulse width, and low 1.5mA max supply current. It serves as a single-chip solution for critical µP power monitoring in battery-backed CMOS RAM systems.

For engineers reviewing the LTC690CS8#PBF datasheet, LTC690CS8#PBF pinout, LTC690CS8#PBF application, or LTC690CS8#PBF equivalent, key selection criteria include guaranteed reset at ultra-low VCC, integrated NMOS/PMOS switchover for RAM backup, user-configurable power-fail detection via PFI, and watchdog timeout periods of 100ms/1.6s with internal oscillator - all in an industry-standard SO-8 package.

Technical Context

The LTC690CS8#PBF implements a bandgap-based voltage reference and three independent comparators (C1 for reset, C2 for battery switchover, C3 for power-fail detection), plus a digital watchdog timer with transition-triggered reset logic. Its charge-pumped NMOS switch delivers up to 50mA to VOUT with 5Ω typical on-resistance during main power operation, while a 125Ω PMOS switch enables low-dropout battery backup.

Reset timing is governed by an internal oscillator (fixed 50ms typical active time) or external clock/capacitor when OSC SEL is low; watchdog timeout defaults to 100ms (short) or 1.6s (long) depending on OSC IN state. All outputs - RESET, WDO, PFO, BATT ON - are open-drain with weak internal 3µA pull-ups, supporting flexible interface to µP NMI, CE, or interrupt lines.

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 MAX690ESA+ and TPS3823DBVR, the LTC690CS8#PBF uniquely integrates battery switchover, watchdog, and power-fail warning in one SO-8 device - eliminating 3–5 external components while enabling true single-chip µP supervision with RAM retention.

Availability

LTC690CS8#PBF is available at Aetrix Electronics and suitable for industrial control PLCs, medical diagnostic equipment, automotive infotainment head units, smart energy meters, and portable instrumentation requiring stable component supply across extended temperature ranges.

Supply support for LTC690CS8#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.

The LTC690 family was designed specifically for robust, integrated microprocessor supervision in mission-critical embedded systems - emphasizing guaranteed low-VCC reset, zero-component battery backup, and configurable power-fail response.

FAQ

What is the guaranteed minimum VCC level at which LTC690CS8#PBF asserts RESET?

The LTC690CS8#PBF guarantees RESET remains logic low down to VCC = 1V, with ISINK = 10µA. This ensures the microprocessor stays held in reset during deep brownout conditions where other supervisors may release prematurely, preventing undefined behavior or memory corruption. The specification is tested and guaranteed over the full 0°C to 70°C operating range.

How does LTC690CS8#PBF manage battery backup for CMOS RAM without external MOSFETs?

The LTC690CS8#PBF integrates a charge-pumped NMOS switch (M1) for main power delivery to VOUT and a PMOS switch (M2) for battery backup. When VCC drops below VBATT minus 50mV, it automatically switches VOUT to VBATT through M2, delivering up to 250µA with only 125Ω on-resistance. No external transistors or diodes are required, simplifying layout and reducing BOM count.

Can the watchdog timeout period of LTC690CS8#PBF be adjusted, and how?

Yes - the LTC690CS8#PBF supports two fixed watchdog timeout periods (100ms short, 1.6s long) selected by the logic state on OSC IN when OSC SEL is high. For custom timing, drive OSC IN with an external clock or connect a capacitor between OSC IN and GND (with OSC SEL low); nominal timeout then scales with external frequency or capacitance per the datasheet formula.

What is the function of the BATT ON pin on LTC690CS8#PBF, and how is it used?

The BATT ON pin is an open-drain logic output that goes low when VOUT is powered from VCC and high when switched to VBATT. It can sink up to 35mA and is commonly used to drive the base of an external PNP transistor, enabling higher-current RAM backup beyond the 50mA limit of the internal NMOS switch. Its state directly reflects the active power source for VOUT.

Does LTC690CS8#PBF support adjustable reset timeout, and if not, what are the alternatives?

No - the LTC690CS8#PBF has a fixed minimum reset active time of 35ms (50ms typical). Adjustable reset timing is only available on the 16-pin LTC691/LTC695 variants. For designs requiring programmable reset duration in an 8-pin package, consider the LTC690CS8#PBF's functional sibling LTC694CS8#PBF (same pinout, identical features except longer 140ms reset pulse).