Analog Devices Inc. LTC2924IGN#PBF

Overview of the LTC2924IGN#PBF Four-Channel Power Supply Sequencer

Modern electronic systems such as ASICs and FPGAs almost invariably require the accurate sequencing and monitoring of multiple voltage rails to prevent bus contention, latch-up, and damage to sensitive devices. The LTC2924IGN#PBF from Analog Devices is a dedicated quad power supply sequencer that addresses these challenges by providing robust, programmable sequencing and monitoring features. This article examines the LTC2924IGN#PBF in detail—supporting engineering design decisions for both selection and integration into power management subsystems.

Main Advantages of the LTC2924IGN#PBF in Power Supply Sequence Control

Engineers evaluating power supply sequencers must scrutinize both the device’s capabilities and integration requirements. The LTC2924IGN#PBF stands out with:

Capability to fully sequence and monitor up to four independent power supplies.

Cascadable architecture, supporting sequencing of additional rails using multiple devices.

Internally regulated charge pump for direct driving of external N-channel MOSFET gates.

Adjustable, component-defined time delay between rails during both power-up and power-down sequences.

Power Good timer for supply turn-on verification and error detection.

Precision input comparators (1% monitoring accuracy).

Fault detection and reporting with automatic supply shut-off upon sequence errors.

Flexible power-off behavior: either in reverse order or all rails simultaneously.

Minimal external component count.

Available in a 16-lead narrow SSOP package for compact PCB layouts.

These features enable the LTC2924IGN#PBF to provide deterministic, reliable sequencing in complex multi-rail environments, making it especially suitable for ASIC-based systems with strict voltage ramp requirements.

Functional Summary Operating Principles of the LTC2924IGN#PBF

At its core, the LTC2924IGN#PBF orchestrates the precise enablement and disablement of up to four voltage rails. Each channel consists of a monitoring input and an enable output:

During Power On, the device sequentially activates each supply (using OUT1–OUT4), observes rail voltage via resistive dividers feeding IN1–IN4, and applies an optional programmable delay (TMR).

The adjustable hysteresis mechanism allows differentiation between turn-on and turn-off voltage thresholds for each supply.

Power Good monitoring (PGT) ensures each rail achieves the correct voltage within a defined time, otherwise a fault is signaled and all rails are deactivated.

Power Off can be sequenced in reverse (last-on, first-off), or all rails can be disabled in parallel upon external command or fault.

The DONE output indicates end-of-sequence (both for power-up and power-down) for system-level coordination or for cascading additional LTC2924IGN#PBF devices.

Control logic, precision comparators, and a charge pump are integrated, greatly simplifying external circuitry while supporting robust sequencing logic for complex systems.

LTC2924IGN#PBF Pin Configuration and Connection Information

Interfacing the LTC2924IGN#PBF to power supplies and control logic is straightforward but must follow specific pin functions for proper behavior:

IN1–IN4: Analog voltage sense inputs; connect to each rail through resistor dividers for voltage monitoring.

OUT1–OUT4: Supply enable outputs; drive either shutdown pins or external N-channel MOSFETs for each sequenced supply.

ON: Master enable input for starting or stopping sequencing, typically driven by a system controller.

DONE: Sequence completion flag (open-drain), usable for system monitoring or cascading.

FAULT: Fault indicator (open-drain); signals sequence, timing, or control errors.

TMR and PGT: Timing and Power Good Timer capacitors for sequence delay and monitoring.

HYS/CFG: Sets hysteresis current, affecting voltage threshold hysteresis for supply detection; also configures cascade position.

VCC and GND: Device power input (3–6V) and ground.

Minimal PCB real estate is needed due to the 16-SSOP package and the general absence of large passives, with timing defined by standard ceramic capacitors for TMR/PGT and precision resistors for detection thresholds.

Essential Design and Deployment Guidelines for the LTC2924IGN#PBF

Several critical engineering points must be addressed for optimal implementation:

Resistive dividers for IN1–IN4 must be calculated for desired turn-on/turn-off voltages, considering external hysteresis current.

Hysteresis resistor (HYS/CFG) is crucial for reliable sequencing, with recommended calculation per 0.5V/I_HYS, ensuring I_HYS is within 0.5µA to 50µA.

Stray capacitance on analog monitor and ON pins can affect timing precision; keep resistive dividers close to the IC.

Timing capacitors (TMR, PGT) must be low-leakage ceramics; selection directly defines delays and fault detection windows.

Careful ground and supply routing is required—especially when cascading multiple LTC2924IGN#PBF devices—to avoid noise issues.

Special attention should be given when turning off supplies near 0.8V or less, as load-dominated discharge currents may induce long fall times.

Sequencing Timing, Fault Monitoring, and Expansion Using the LTC2924IGN#PBF

The LTC2924IGN#PBF offers significant flexibility and safety through its timing and fault-handling subsystems:

The TMR pin sets programmable per-rail delays for both up and down sequencing (200ms/µF); leaving TMR floating minimizes this delay.

The PGT pin defines the maximum allowed time for each supply to reach threshold after enablement; if exceeded, a fault is declared.

Fault detection is multifaceted, covering sequence errors, timing overruns, system enable/disable errors, and externally commanded faults.

If a detected fault occurs, all OUT pins are pulled low, and the FAULT pin is asserted.

For large designs, two or more LTC2924IGN#PBF devices can be cascaded to sequence additional supplies (up to virtually any number, limited by board area and system architecture), with shared FAULT reporting and correct configuration at HYS/CFG and DONE interconnects.

Cascading requires adherence to signal integrity best practices (minimizing parasitics, shielding critical traces, proper sequential configuration) and pull-up strategies for open-drain outputs.

LTC2924IGN#PBF Example Use Cases

The LTC2924IGN#PBF is deployed in numerous advanced electronic systems by virtue of its flexible supply control:

FPGA or ASIC core/multiple I/O supply sequencing to prevent latch-up during initialization or shutdown.

Communication systems, industrial control, or network infrastructure, where rail order and verification are critical for reliability.

Scenarios requiring customizable inter-rail timing—for example, when certain subsystems must fully stabilize before others are powered.

Systems demanding fault tolerance, where any rail’s failure or delayed response must trigger immediate protection.

Large-scale power architectures, with more than four rails, using cascaded devices.

The part can support series MOSFET control, direct shutdown pin driving, negative rail sequencing, multi-rail delivery, and adjusted delays for complex system bring-up/shutdown.

Alternative or Substitute Models for the LTC2924IGN#PBF

For design flexibility and supply chain assurance, it’s prudent to consider alternatives with similar features. While the LTC2924IGN#PBF provides a compelling balance of integration and accuracy, related models (often from the same manufacturer) include:

Analog Devices’ LTC2923: A 2/3-channel power supply sequencer for less-complex designs.

LTC2925: A 6-channel sequencer with PMBus control for digital interface requirements.

LTC2927: A high-voltage six-channel sequencer for applications demanding higher voltage ranges.

Texas Instruments’ TPS386000 or MAX6819/20 from Maxim Integrated: Multi-voltage supervisor/sequencer ICs with alternative feature sets suitable for related scenarios.

Device selection should prioritize channel count, voltage range, sequencing/monitoring accuracy, cascaded expansion needs, package type, and the available feature set including fault detection and timing programmability.

Conclusion

The LTC2924IGN#PBF from Analog Devices offers highly-integrated, programmable, and precise sequencing for multi-rail power subsystems commonly found in modern digital systems. With integrated charge pump, programmable timing, fault detection, and cascadable architecture, the LTC2924IGN#PBF substantially reduces complexity compared to discrete logic, ensuring safe and error-free power-up and power-down behavior. Proper device selection, calculation of external component values, and system-level integration will enable engineering teams to deploy robust power delivery architectures, benefitting from the flexibility and safety of a well-designed sequencer IC. When considering the LTC2924IGN#PBF, engineers are empowered with a solid foundation for both straightforward and highly-scaled power management solutions.