Analog Devices Inc. LTC2938IMS#PBF

Overview

LTC2938IMS#PBF from Analog Devices (formerly Linear Technology) is a configurable 4-supply voltage monitor IC with integrated watchdog timer, reset output, and programmable threshold selection via VPG pin. It monitors up to four independent supply rails (e.g., 5V, 3.3V, 2.5V, 1.8V), provides ±1.5% threshold accuracy over temperature, supports adjustable reset (2–4 ms/nF) and watchdog (20–40 ms/nF) timeouts, and operates down to VCC = 1V. It is used in multivoltage embedded systems requiring reliable power-on reset and software supervision.

For engineers reviewing the LTC2938IMS#PBF datasheet, LTC2938IMS#PBF pinout, LTC2938IMS#PBF application, or LTC2938IMS#PBF equivalent, key selection criteria include guaranteed RST assertion at VCC ≥ 1V, 12-lead MSOP package compatibility, ±1.5% voltage threshold accuracy, 80μA typical supply current, and support for both positive and negative adjustable inputs (–ADJ mode on V4).

Technical Context

The LTC2938IMS#PBF implements six high-impedance comparator inputs (V1–V4) with user-selectable thresholds via a 1% resistive divider on VPG, enabling 16 preset combinations of 5V/3.3V/2.5V/1.8V/1.5V/1.2V or ADJ/–ADJ modes. Its internal bandgap reference (1.210V ±18mV) feeds VREF and enables precise threshold scaling.

Reset and watchdog timing are capacitor-programmed: CRT sets tRST (2 ms/nF), CWT sets tWD (20 ms/nF); both tolerate leakage-sensitive ceramic capacitors. The RST and WDO outputs feature weak 6μA pull-ups to V2, requiring external pull-ups when V2 ≤ 2.5V to meet VOH requirements of downstream logic.

Key Specifications

Pinout & Package

Package: 12-Lead Plastic MSOP (MS package), 3.0 mm × 3.0 mm body, exposed pad optional, θJA = 130°C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6361AUK+T and TPS3808G33DBVR, the LTC2938IMS#PBF delivers unique value through single-chip 4-rail configurability, ±1.5% accuracy, and integrated watchdog - reducing component count, improving system-level reliability, and enabling field-upgradable voltage monitoring without hardware changes.

Availability

LTC2938IMS#PBF is available at Aetrix Electronics and suitable for desktop computers, telecom equipment, and network servers requiring stable component supply, long-term obsolescence management, and industrial-grade temperature performance.

Supply support for LTC2938IMS#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, serving industrial, automotive, communications, and healthcare markets.

The LTC2938 belongs to ADI's precision power monitoring product line, designed specifically for multivoltage systems needing accurate, configurable, and watchdog-enabled reset supervision in space-constrained and thermally demanding environments.

FAQ

What is the minimum VCC voltage required for guaranteed RST output behavior in the LTC2938IMS#PBF?

The LTC2938IMS#PBF guarantees correct RST logic state down to VCC = 1V. This means RST will remain asserted (low) as V1 or V2 drops below operating range, ensuring fail-safe reset during brownout conditions. Below 1V, internal circuitry may become indeterminate, but the 1V guarantee covers most real-world power collapse scenarios encountered in industrial and computing applications using the LTC2938IMS#PBF.

How does the VPG pin configure the voltage monitoring thresholds on the LTC2938IMS#PBF?

The VPG pin accepts a resistive divider between VREF (1.210V) and GND to select one of 16 predefined threshold combinations for V1–V4. For example, connecting VPG to 0.156×VREF configures the LTC2938IMS#PBF to monitor 3.3V, 2.5V, ADJ, and ADJ rails. The part samples VPG during a 150μs power-up window - no external capacitance is permitted on VPG to avoid configuration errors in the LTC2938IMS#PBF.

Can the LTC2938IMS#PBF monitor negative supply voltages?

Yes - the LTC2938IMS#PBF supports negative rail monitoring via the –ADJ mode on V4. In this mode, VREF (1.210V) serves as a level-shift reference: an external resistor divider between the negative supply and VREF connects to V4, enabling accurate trip-point setting (e.g., –5V ±5%). This eliminates need for external op-amps or charge pumps in designs using the LTC2938IMS#PBF for dual-polarity systems.

What is the purpose of the CRT and CWT pins on the LTC2938IMS#PBF?

CRT sets the reset timeout period (tRST = 2 ms/nF) - the duration RST remains low after all supplies exceed thresholds. CWT sets the watchdog timeout period (tWD = 20 ms/nF) - the maximum interval between WDI transitions before WDO and RST assert. Both pins connect to GND via external capacitors; leaving them unconnected yields minimum delays (~20μs and ~200μs respectively), while grounding CWT disables the watchdog entirely in the LTC2938IMS#PBF.

Does the LTC2938IMS#PBF require external pull-up resistors on RST and WDO?

Yes - when V2 monitors 2.5V or lower (e.g., 1.8V, 1.2V), the internal 6μA pull-up to V2 cannot ensure VOH exceeds typical VIH thresholds (e.g., 2.0V for 3.3V logic). External pull-up resistors to the target interface supply (e.g., 3.3V) are mandatory to guarantee valid high-level signaling. This requirement is explicitly documented in the LTC2938IMS#PBF datasheet for reliable interoperation with downstream FPGAs, MCUs, or ASICs.