Analog Devices Inc. LTC690CN8#PBF

Overview

LTC690CN8#PBF 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 a charge-pumped NMOS VOUT switch (50mA, 5Ω typical R_DS(on)), internal 1.3V reference for PFI comparator, and fixed 35ms minimum reset active time. Used in battery-backed CMOS RAM systems requiring stable low-dropout auxiliary power and early power-fail detection.

For engineers reviewing the LTC690CN8#PBF datasheet, LTC690CN8#PBF pinout, LTC690CN8#PBF application, or LTC690CN8#PBF equivalent, this page delivers verified circuit role, exact pin functions, confirmed reset threshold hysteresis (40mV), battery switchover thresholds (70mV up / 50mV down), and real-world timing behavior under VCC decay and VBATT transition.

Technical Context

The LTC690CN8#PBF implements a dual-path power management architecture: a precision bandgap-referenced voltage comparator (C1) monitors VCC against 4.65V nominal threshold with 40mV hysteresis, while a separate comparator (C2) controls automatic switchover between VCC and VBATT using 70mV/50mV thresholds and 20mV hysteresis. Its internal oscillator sets fixed 35ms min reset pulse width and 1.6s/100ms watchdog timeout periods.

It features a charge-pumped NMOS VOUT switch delivering up to 50mA at ≤5Ω on-resistance during main power operation, and a 125Ω PMOS switch enabling <1µA standby current in battery-backup mode. The RESET output remains logic-low down to VCC = 1V, ensuring reliable µP hold-down during brownout.

Key Specifications

Pinout & Package

Package: 8-lead PDIP (N8), 0°C to 70°C operating range, 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 MAX690CPA+ and TPS3823DBVR, the LTC690CN8#PBF provides integrated battery switchover, guaranteed 1V reset hold, and power-fail warning in a single 8-pin package - eliminating 3–5 external components required by alternatives to achieve equivalent system-level functionality.

Availability

LTC690CN8#PBF is available at Aetrix Electronics and suitable for industrial control PLCs, medical portable monitors, automotive infotainment head units, point-of-sale terminals, and battery-backed data loggers requiring stable component supply across extended production lifecycles.

Supply support for LTC690CN8#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 (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 microprocessor-based systems needing integrated power monitoring, battery backup, power-fail warning, and watchdog timing - consolidating functions previously requiring 4–6 discrete ICs into one compact solution.

FAQ

What is the guaranteed minimum reset assertion voltage for LTC690CN8#PBF?

The LTC690CN8#PBF guarantees RESET remains logic-low down to VCC = 1V, ensuring the microprocessor stays in a known reset state even during severe brownout conditions. This specification is tested and guaranteed over the full 0°C to 70°C operating temperature range, and is independent of load or VBATT voltage. The LTC690CN8#PBF achieves this via dedicated low-voltage reset circuitry that operates below standard CMOS logic thresholds.

Does LTC690CN8#PBF support adjustable reset timeout periods?

No, the LTC690CN8#PBF has a fixed minimum reset active time of 35ms, determined by its internal oscillator. Adjustable reset timing is only available on the 16-pin LTC691 and LTC695 variants, which include OSC SEL and OSC IN pins for external clock or capacitor configuration. The LTC690CN8#PBF uses the internal oscillator exclusively and does not provide external adjustment capability.

Can LTC690CN8#PBF drive CMOS RAM directly without external components?

Yes, the LTC690CN8#PBF can drive CMOS RAM directly via its VOUT pin, which delivers up to 50mA with ≤5Ω typical on-resistance from the charge-pumped NMOS switch. When VCC is present, VOUT tracks VCC minus small dropout; during battery backup, it connects to VBATT through a 125Ω PMOS switch. No external pass transistor or diode is required for standard RAM loads, though heavy transient currents (>50mA) require the LTC691/LTC695 or external boost.

What is the function of the PFI and PFO pins on LTC690CN8#PBF?

The PFI (Power-Fail Input) pin accepts a user-defined voltage divider signal referenced to the LTC690CN8#PBF's internal 1.3V comparator threshold. When PFI falls below 1.3V, the PFO (Power-Fail Output) pin goes low to signal impending supply failure - typically used to trigger µP interrupts for controlled shutdown. PFO is open-drain and requires an external pull-up; it is forced low when VCC drops below VBATT, disabling false warnings during battery backup mode.

How does LTC690CN8#PBF handle battery switchover between VCC and VBATT?

The LTC690CN8#PBF uses comparator C2 to monitor the VCC–VBATT differential. When VCC rises to 70mV above VBATT, VOUT connects to VCC via the NMOS switch; when VCC falls to 50mV above VBATT, VOUT switches to VBATT via the PMOS switch. This 20mV hysteresis prevents chatter near the switchover point. In battery-backup mode, supply current drops to ≤1µA, and all outputs except RESET, RESET, and WDO assume defined states per Table 1 in the datasheet.