Overview
The LM3881 Simple Power Sequencer, produced by Texas Instruments (formerly National Semiconductor), is a versatile component designed to control the power-up and power-down sequences of multiple power supplies. This device is particularly useful in systems where controlled sequencing is crucial to avoid latch conditions or large inrush currents. The LM3881 is available in a VSSOP-8 package, offering a tiny footprint that is ideal for space-constrained designs.
The sequencer features a precision enable pin and three open-drain output flags that sequentially release after individual time delays, allowing for the controlled startup of connected power supplies. The output flags can be inverted using the INV pin, making it adaptable to various power supply configurations.
Key Specifications
| Parameter | Min | Max | Unit |
|---|---|---|---|
| Input Supply Voltage (VCC to GND) | 2.7 | 5.5 | V |
| Enable, Invert, TADJ, FLAG1, FLAG2, FLAG3 to GND | -0.3 | VCC + 0.3 | V |
| Junction Temperature | -40 | 125 | °C |
| Quiescent Current | 80 | µA | |
| Junction-to-ambient thermal resistance (RθJA) | 224.5 | °C/W | |
| Package Type | VSSOP-8 | ||
| Body Size (Nominal) | 3.00 mm x 3.00 mm |
Key Features
- Easiest method to sequence multiple power rails, including switching and linear regulators.
- Low quiescent current of 80 µA.
- Input voltage range of 2.7 V to 5.5 V.
- Output invert feature allows for active high or active low logic modes.
- Timing controlled by a small external capacitor.
- Glitch-free operation on the enable pin.
- Tiny footprint in VSSOP-8 package.
Applications
- Security Cameras: Ensures controlled power sequencing to prevent system failures.
- Servers: Critical for managing power supplies in server systems to avoid latch conditions.
- Networking Elements: Used in network devices to sequence power supplies efficiently.
- FPGA Sequencing: Essential for sequencing power in Field-Programmable Gate Arrays (FPGAs).
- Microprocessor and Microcontroller Sequencing: Helps in managing power supplies for microprocessors and microcontrollers.
- Multiple Supply Sequencing: Ideal for systems requiring the sequencing of multiple power supplies.
Q & A
- What is the primary function of the LM3881?
The LM3881 is designed to control the power-up and power-down sequences of multiple power supplies, preventing latch conditions and large inrush currents.
- What is the input voltage range for the LM3881?
The input voltage range is from 2.7 V to 5.5 V.
- How is the timing sequence controlled in the LM3881?
The timing sequence is controlled by an external capacitor connected to the TADJ pin.
- What is the purpose of the INV pin on the LM3881?
The INV pin allows the user to invert the logic of the output flags, making them either active high or active low.
- What is the quiescent current of the LM3881?
The quiescent current is 80 µA.
- In what package is the LM3881 available?
The LM3881 is available in a VSSOP-8 package.
- What are some common applications of the LM3881?
Common applications include security cameras, servers, networking elements, FPGA sequencing, and microprocessor/microcontroller sequencing.
- How does the LM3881 handle power-down sequencing?
During power-down, the flags are sequentially pulled low after appropriate delays, ensuring a controlled shutdown.
- What is the significance of the enable (EN) pin on the LM3881?
The EN pin controls the start of the power-up sequence and ensures glitch-free operation.
- How should the layout be designed for the LM3881?
The layout should minimize trace lengths and ensure pullup resistors are placed close to the flag output pins and the positive input supply.
