Texas Instruments LMC6953CM/NOPB

Overview

LMC6953CM/NOPB from Texas Instruments is a PCI Local Bus Power Supervisor IC compliant with PCI Specification Revision 2.1, monitoring both 5V and 3.3V supplies with independent over/under-voltage detection, power-failure sensing (5V falling below 3.3V by ≤300 mV), and active-low open-drain RESET output. It asserts reset in ≤490 ns for supply faults and holds RESET low for 100 ms after recovery, supporting desktop PCs and PCI-based add-in cards.

For engineers reviewing the LMC6953CM/NOPB datasheet, LMC6953CM/NOPB pinout, LMC6953CM/NOPB application, or LMC6953CM/NOPB equivalent, key selection criteria include PCI 2.1 compliance, dual-supply voltage supervision thresholds (e.g., VL5 = 4.10–4.70 V, VH3.3 = 3.60–4.30 V), manual reset input, adjustable 100 ms reset delay via CEXT, and SOIC-8 packaging with VDD/5V pin separation for backup capacitor support.

Technical Context

The LMC6953CM/NOPB implements five internal comparators-two for 5V window detection (over/under), two for 3.3V window detection, and one dedicated power-failure comparator comparing 5V and 3.3V pins-with all comparator positive supplies tied to VDD. Its reset logic combines fault detection outputs using wired-OR behavior, ensuring RESET goes low on any detected fault (power failure, over/under-voltage, or MR assertion) and remains low for a fixed 100 ms after fault clearance.

It features a built-in bandgap reference for stable threshold generation across temperature (−40°C to +85°C), operates from VDD = 1.55 V to 6 V, and delivers fast response: ≤90 ns for power-failure events and ≤490 ns for over/under-voltage transitions. The external capacitor on CEXT pin linearly adjusts reset delay timing without requiring additional discrete timing components.

Key Specifications

Pinout & Package

LMC6953CM/NOPB is housed in an 8-pin SOIC (Package Drawing D), 3.9 mm × 4.9 mm body, 1.75 mm max height, RoHS-compliant with CuSn lead finish and moisture sensitivity level (MSL) Level-1.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar power supervisor applications.

Compared with LMC6953CM/NOPB, TPS3808G18 offers lower supply voltage support but omits critical PCI functions like power-failure detection and dual-rail windowing, while MAX6953 provides mechanical compatibility but fails to meet PCI 2.1's 300 mV power-failure differential and 490 ns response time requirements.

Availability

LMC6953CM/NOPB is available at Aetrix Electronics and suitable for desktop PCs, PCI-based servers, network equipment, and industrial embedded controllers requiring stable component supply across long-lifecycle deployments.

Supply support for LMC6953CM/NOPB 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

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and connectivity technologies, with decades of experience in power management and interface solutions.

The LMC6953CM/NOPB belongs to TI's legacy PCI power supervision product line, engineered specifically to enforce PCI Specification Revision 2.1 compliance in desktop, server, and industrial computing platforms.

FAQ

What is the minimum VDD voltage required for reliable RESET assertion in LMC6953CM/NOPB?

The LMC6953CM/NOPB specifies a minimum VDD of 1.55 V to ensure consistent RESET assertion during brown-out conditions. This allows the device to remain functional and assert reset even when the main 5V supply collapses significantly, supporting robust system initialization integrity. Below 1.55 V, comparator accuracy and output drive capability degrade, risking undetected faults. The LMC6953CM/NOPB datasheet confirms this limit under DC Electrical Characteristics.

How does the power-failure detection function work in LMC6953CM/NOPB?

The LMC6953CM/NOPB detects power failure by continuously comparing the 5V and 3.3V supply pins: RESET is asserted when the 5V pin falls ≤300 mV below the 3.3V pin, with a maximum response time of 90 ns. This differential sensing is implemented via a dedicated internal comparator referenced to the 3.3V rail, enabling rapid shutdown before bus contention or data loss occurs. The function operates independently of absolute voltage levels, making it effective during asymmetric supply collapse.

Can LMC6953CM/NOPB monitor only one supply voltage, or is dual-supply operation mandatory?

LMC6953CM/NOPB is designed for mandatory dual-supply monitoring: both 5V and 3.3V inputs must be connected for full PCI 2.1 compliance and correct reset behavior. The device asserts RESET if either supply violates its window or if the power-failure condition occurs; leaving either pin unconnected disables critical fault detection paths. While VDD can be tied to 5V in simplified applications, the 5V and 3.3V pins must still receive valid voltages to satisfy the truth table and timing specifications defined in the LMC6953CM/NOPB datasheet.

What is the purpose of separating VDD and 5V pins on LMC6953CM/NOPB?

The VDD and 5V pins are separated to enable backup power functionality: VDD supplies internal comparators and can be connected to a capacitor that sustains operation during brief 5V interruptions, while the 5V pin feeds only the monitoring comparators. This architecture allows the LMC6953CM/NOPB to detect and respond to power failure even if the main 5V rail collapses, provided the backup capacitor maintains VDD above 1.55 V. The separation is essential for achieving the specified 90 ns power-failure response and is explicitly detailed in the LMC6953CM/NOPB application note.

Is LMC6953CM/NOPB still recommended for new designs?

No-LMC6953CM/NOPB is marked NRND (Not Recommended for New Designs) per TI's Package Option Addendum. It remains in production to support existing customers but TI advises migration to newer alternatives for new projects. Designers should verify current status via TI's official product folder and consider functional replacements only after validating electrical, timing, and compliance requirements against the LMC6953CM/NOPB datasheet and PCI 2.1 specification.