Analog Devices Inc. LTC2938HMS#PBF

Overview

LTC2938HMS#PBF from Analog Devices (formerly Linear Technology) is a configurable 4-supply voltage monitor IC with integrated watchdog timer, reset output, and ±1.5% threshold accuracy over temperature. It supports up to four user-selectable supply voltages (e.g., 5V, 3.3V, 2.5V, 1.8V, ADJ, –ADJ), adjustable reset (2–4 ms/nF) and watchdog (20–40 ms/nF) timeouts via external capacitors, and operates from –40°C to 125°C. It is used in multivoltage embedded systems requiring reliable power-up/power-down supervision and software fault detection.

For engineers reviewing the LTC2938HMS#PBF datasheet, LTC2938HMS#PBF pinout, LTC2938HMS#PBF application, or LTC2938HMS#PBF equivalent, key selection criteria include guaranteed RST assertion down to VCC = 1V, 80μA typical supply current, glitch-immune comparators, 12-lead MSOP package, and support for both positive and negative adjustable thresholds via VPG programming.

Technical Context

The LTC2938HMS#PBF implements six independent high-impedance voltage comparators - four inputs (V1–V4) with programmable thresholds selected via a 1% resistive divider on VPG - and uses the greater of V1 or V2 as its internal VCC supply. Its bandgap reference (1.210V ±18mV) feeds both the VPG interface and the –ADJ mode level shift, enabling accurate negative rail monitoring.

Reset and watchdog timing are capacitor-controlled: CRT sets tRST (2ms/nF), CWT sets tWD (20ms/nF); both outputs (RST, WDO) feature weak 6μA pull-ups to V2, with external pull-up required when V2 ≤ 2.5V to meet VOH requirements of downstream logic. The device enters configuration mode for ~150μs at power-up to sample VPG before enabling monitoring.

Key Specifications

Pinout & Package

Package: 12-Lead Plastic MSOP (3mm × 4.4mm, 0.65mm pitch), exposed pad optional for thermal enhancement. Pin count and layout match LTC2938 family; not compatible with LTC2939's 16-lead MSOP.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6369ESA+ and TPS3808G33DBVR, the LTC2938HMS#PBF uniquely combines 4-rail configurability, ±ADJ threshold flexibility, integrated watchdog, and H-grade temperature range in a compact MSOP - making it irreplaceable for space-constrained, multirail industrial and automotive systems requiring coordinated reset and software fault recovery.

Availability

LTC2938HMS#PBF is available at Aetrix Electronics and suitable for desktop computers, automotive ECUs, and telecom line cards requiring stable component supply with extended temperature qualification and long-term lifecycle support.

Supply support for LTC2938HMS#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 LTC2938 belongs to ADI's precision power monitoring product line, designed specifically for mission-critical multivoltage systems where deterministic reset behavior, watchdog reliability, and wide-temperature operation are mandatory.

FAQ

What is the maximum operating temperature for the LTC2938HMS#PBF?

The LTC2938HMS#PBF is rated for operation from –40°C to +125°C, meeting the H-grade specification. This makes it suitable for under-hood automotive applications, industrial controllers, and telecom equipment deployed in uncontrolled ambient environments. Thermal performance is supported by the MSOP package's θJA of 110°C/W.

How do I configure the LTC2938HMS#PBF for monitoring a –12V rail?

To monitor a –12V rail with the LTC2938HMS#PBF, configure V4 in –ADJ mode using Mode 1 (V1=5V, V2=3.3V, V3=ADJ, V4=–ADJ) and connect a resistive divider between –12V and VREF (1.21V). The trip point is calculated as VTRIP = –(R3/R4) × VREF. For –12V → –11.3V trip, use R3 = 1130kΩ and R4 = 121kΩ per Table 3 in the datasheet.

Does the LTC2938HMS#PBF require external pull-up resistors on RST and WDO?

Yes - external pull-up resistors are required on RST and WDO when V2 is configured to monitor 2.5V or lower (e.g., 1.8V, 1.5V, 1.2V). The internal 6μA pull-up to V2 cannot guarantee VOH above typical VIH thresholds (e.g., 2.0V for 3.3V logic). Pull to the target logic rail (e.g., 3.3V) with a 10–100kΩ resistor to ensure proper interfacing.

Can the LTC2938HMS#PBF monitor six supply rails?

No - the LTC2938HMS#PBF monitors up to four supply rails (V1–V4). The six-rail variant is the LTC2939 (e.g., LTC2939HMS#PBF), which uses a 16-lead MSOP package and adds V5 and V6 inputs. Attempting to use LTC2938HMS#PBF for six rails will result in unmonitored supplies and potential system instability.

What capacitor values are recommended for a 100ms reset timeout and 1s watchdog timeout with the LTC2938HMS#PBF?

For a ~100ms reset timeout, use CRT = 47nF (tRST ≈ 2ms/nF × 47nF = 94ms). For a ~1s watchdog timeout, use CWT = 47nF (tWD ≈ 20ms/nF × 47nF = 940ms). Both capacitors must be low-leakage ceramic types (e.g., X7R, C0G) with ≤10% tolerance; avoid electrolytics or high-leakage dielectrics that degrade timing accuracy.