LTC2950ITS8-1#TRMPBF

LTC2950ITS8-1#TRMPBF

Introduction

LTC2950ITS8-1#TRMPBF is a 4-channel micropower supply tracker and watchdog timer manufactured by Analog Devices (formerly Linear Technology). It is designed to monitor multiple power supply rails in complex electronic systems, ensuring that voltages remain within safe operating limits. The device integrates undervoltage (UV) and overvoltage (OV) monitoring, a precision watchdog timer, and a manual reset input to provide comprehensive system protection.

The suffix "-1" indicates a specific fixed threshold voltage for the primary sense input (V1 = 2.5V), while the other inputs (V2, V3, V4) remain adjustable via external resistors. The "ITS8" denotes the package type: an 8-pin TSOT-23 (Thin Small Outline Transistor) package, ideal for space-constrained designs. The "#TRMPBF" suffix confirms the part is supplied in Tape & Reel (TR) for automated surface-mount assembly, is Lead-Free (PbF), and is RoHS compliant. This IC is critical for preventing system corruption in FPGAs, DSPs, and multi-rail industrial power supplies.

Key Features

• Multi-Rail Monitoring: Simultaneously monitors four power supplies (V1, V2, V3, V4).
  • V1: Fixed 2.5V threshold (for the "-1" version).
  • V2, V3, V4: Adjustable thresholds (1V to 5V) set by external resistor dividers.
• Watchdog Timer: Precision watchdog with a selectable timeout period (100ms to 1.6s) to detect software crashes or hangs.
• Reset Generation: Asserts a reset signal (RST) if any monitored voltage falls out of tolerance or if the watchdog timer expires.
• Manual Reset (MR): Active-low input allows an external button or MCU to trigger a system reset.
• Glitch Filtering: Integrated filtering rejects fast transient noise (glitches) on the supply lines to prevent false resets.
• Low Power Operation:
  • Supply Current: Typically 7µA (ultra-low power for always-on monitoring).
  • Watchdog Current: ~1µA.
• Flexible Output: The RST pin is an open-drain output, allowing wired-OR logic and level translation to different logic voltages (1.8V, 3.3V, 5V).
• Enable/Power-Good Function: Can be configured to act as a Power-Good indicator or to enable a DC/DC converter after all rails are stable.

Typical Specification Table

Typical Applications

• FPGA & SoC Power Sequencing: Monitoring core voltage (1.0V/1.2V), I/O voltage (1.8V/2.5V), and auxiliary rails (3.3V/5V) in Xilinx/Intel/Lattice FPGAs.
• Industrial Automation: PLCs and robotics controllers where 24V, 12V, 5V, and 3.3V rails must be verified before allowing motor operation.
• Server & RAID Systems: Ensuring all power rails in a blade server or storage array are stable before booting the OS.
• Medical Devices: Patient monitors and infusion pumps requiring high reliability and immunity to power brownouts.
• Automotive Infotainment: Monitoring 12V battery, 5V logic, and 3.3V processor rails in head units and telematics.
• Battery-Powered Equipment: Portable data loggers and handheld instruments where low quiescent current (7µA) preserves battery life.

Development & Design Notes

1. Setting Thresholds (V2, V3, V4):
Since V1 is fixed at 2.5V for the "-1" version, V2, V3, and V4 use external resistor dividers connected to the VCC reference (internal 1.2V reference typically).

• Formula: VSENSE​=VREF​×(1+RBOTTOM​RTOP​​)
• Ensure resistor values are high (e.g., 100kΩ - 1MΩ) to minimize leakage current draw from the supply rail.

2. Watchdog Configuration (WDI):
The watchdog timer prevents software lockups. The host MCU must toggle the WDI pin periodically (before the timeout expires).

• If the WDI pin is left high or low for too long, the RST pin is asserted.
• Connect a capacitor from the WDI pin to ground to set the timeout duration (check datasheet graph for capacitance vs. time).

3. Reset Timing (CDELAY):
The reset pulse width (time RST stays low after a fault) is determined by an external capacitor (CDELAY​) connected to the CDELAY pin.

• tRESET​≈6.8×104×CDELAY​ (in Farads).
• Example: 0.1µF capacitor yields ~6.8ms reset pulse.

4. Manual Reset (MR) Pin:
The MR pin is active low. It should be pulled up to VCC via a resistor (e.g., 10kΩ). A momentary switch to ground will trigger an immediate reset. Ensure debouncing if using a mechanical switch.

5. Open-Drain Output (RST):
The RST pin is open-drain. You must connect a pull-up resistor (typically 4.7kΩ to 10kΩ) from RST to the logic voltage of the host processor (e.g., 3.3V). This allows the LTC2950 to reset a 1.8V or 5V processor safely.

6. Power Sequencing:
The LTC2950 does not require a specific power-up sequence for its own supply (VCC), but VCC must be present and stable before it can monitor the other rails. If VCC drops below ~2V, the device may not function correctly.