Analog Devices Inc. LTC1536CS8#PBF

Overview

LTC1536CS8#PBF from Analog Devices (formerly Linear Technology) is a precision triple supply monitor IC designed for PCI local bus applications. It simultaneously monitors 5V (±5%), 3.3V (±0.3V), and an adjustable input (e.g., 1.000V ±0.75% threshold accuracy), delivers active-high and active-low reset outputs, and guarantees correct RST state down to VCC3 ≥ 1V or VCC5 ≥ 1V - enabling robust power-up/down sequencing in desktop and notebook motherboards.

For engineers reviewing the LTC1536CS8#PBF datasheet, LTC1536CS8#PBF pinout, LTC1536CS8#PBF application, or LTC1536CS8#PBF equivalent, key selection considerations include PCI tFAIL compliance (≤450 ns), 200ms internal reset delay, manual pushbutton soft-reset capability (100µs pulse), glitch immunity via dual-threshold comparators, and operation in narrow SO-8 package with 100µA typical supply current.

Technical Context

The LTC1536CS8#PBF integrates three independent voltage sense inputs (VCC5, VCC3, VCCA) feeding parallel fast/accurate comparator pairs per rail to meet PCI tFAIL timing while maintaining ±0.75% threshold accuracy. Its internal reset generator asserts RST low for ≥200ms after all supplies stabilize above thresholds or after PBR release following long-press (>2s).

It features dual open-drain reset outputs (RST and SRST) with weak internal 6µA pull-ups to VCC3, supporting OR-tie with other reset sources; the PBR input includes 20ms debounce and supports ESD hardening via external series resistor. Power detect logic automatically selects VCC3 or VCC5 as gate drive source for the RST output FET.

Key Specifications

Pinout & Package

Package: 8-lead plastic SO (narrow, 0.150-inch width), RoHS-compliant, JEDEC MS-012AC compliant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC1326CMS8#PBF, the LTC1536CS8#PBF adds PBR-driven soft/hard reset and PCI-optimized fast response, while LTC1536IS8#PBF extends thermal range without altering timing or interface - making the C-grade version the most cost-effective choice for standard computing applications.

Availability

LTC1536CS8#PBF is available at Aetrix Electronics and suitable for desktop motherboards, notebook platforms, and PCI expansion card designs requiring stable component supply, PCI-compliant reset timing, and dual-mode pushbutton reset capability.

Supply support for LTC1536CS8#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 and maintains its precision analog and power management portfolio. Linear's legacy design ethos emphasizes high-accuracy, low-power, and application-specific integration.

The LTC1536CS8#PBF belongs to Linear's precision supply monitor product line, engineered specifically for PCI-compliant computing systems requiring simultaneous multi-rail supervision, fast fault response, and flexible reset generation - including soft-reset preservation of DRAM state.

FAQ

What is the primary function of the LTC1536CS8#PBF in a PCI-based system?

The LTC1536CS8#PBF serves as a precision triple-supply monitor that ensures reliable system reset generation during power-up, brownout, and power-down events. In PCI-based systems, it guarantees compliance with tFAIL timing (≤450ns) when either the 5V or 3.3V rail drops out of specification, and it supports both hard and soft reset modes via the PBR input - directly enabling robust motherboard and expansion card reset behavior as defined in PCI Local Bus Specification Rev 2.1. The LTC1536CS8#PBF achieves this using dual-threshold comparators and automatic VCC3/VCC5 gate-drive selection.

Does the LTC1536CS8#PBF support operation with only one supply rail active?

Yes, the LTC1536CS8#PBF guarantees correct RST output state when either VCC3 ≥ 1V or VCC5 ≥ 1V, allowing functional reset assertion even during asymmetric power sequencing or partial rail failure. This is achieved through internal power-detect logic that selects the higher of VCC3 or VCC5 to drive the RST output FET. The LTC1536CS8#PBF does not require both rails to be present simultaneously to maintain valid reset signaling - a key feature for brownout resilience in multi-voltage systems.

How does the PBR input differentiate between soft and hard reset on the LTC1536CS8#PBF?

The PBR input on the LTC1536CS8#PBF uses an internal timer to distinguish press duration: a low pulse shorter than ≈2 seconds (tPB) triggers a 100µs soft reset on SRST, preserving DRAM refresh; a low pulse longer than ≈2 seconds forces RST low and holds it for 200ms after PBR release - equivalent to a power-on reset. The LTC1536CS8#PBF includes 20–35ms debounce on PBR to reject contact bounce, ensuring deterministic mode selection regardless of mechanical switch characteristics.

Can the VCCA pin of the LTC1536CS8#PBF be used for monitoring a DC/DC converter feedback node?

Yes, the VCCA pin of the LTC1536CS8#PBF is a high-impedance 1.000V threshold input designed explicitly for such use cases. When tied to the feedback divider of a DC/DC regulator (e.g., via resistive divider scaling output voltage to 1.000V), it monitors "power good" status or detects regulation loss. The LTC1536CS8#PBF's ±0.75% accuracy and low input current (<15nA) ensure minimal loading and high trip-point stability - making it suitable for closed-loop supervision without affecting converter regulation.

What package type and lead finish does the LTC1536CS8#PBF use?

The LTC1536CS8#PBF uses an 8-lead plastic small-outline (SO-8, narrow 0.150-inch body), designated S8 package per Linear Technology drawing #05-08-1610. It features RoHS-compliant, lead-free (Pb-free) termination with matte tin plating over nickel underplate, indicated by the #PBF suffix. The part marking "1536" appears on the top surface, and the device is rated for 0°C to 70°C operation with θJA = 150°C/W.