LM2588T ADJ - Monolithic Switching Regulator

Overview

The LM2588T ADJ is a monolithic integrated circuit designed for flyback, step-up (boost), and forward converter applications. This highly versatile regulator is part of the LM2588 series, which includes fixed output voltage versions (3.3V, 5.0V, 12V) as well as an adjustable output variant. The device incorporates advanced control features and protection mechanisms, making it suitable for demanding power supply designs in industrial, automotive, and consumer applications.

With its integrated architecture, the LM2588T ADJ simplifies power supply design while delivering robust performance. The current mode control architecture provides excellent line and load regulation, while cycle-by-cycle current limiting ensures reliable operation under fault conditions.

Key Features

• Adjustable output voltage version (ADJ)
• Input voltage range: 4V to 40V
• Integrated 5A NPN switch
• Current mode control architecture
• 52kHz fixed frequency internal oscillator
• Soft-start function for controlled startup
• External shutdown capability
• ±4% output voltage tolerance
• Thermal shutdown protection
• Cycle-by-cycle current limiting
• Available in TO-220 package

Applications

The LM2588T ADJ is suitable for a wide range of power conversion applications, including:

• DC-DC boost converters
• Flyback converters
• Forward converters
• Industrial power supplies
• Automotive power systems
• Battery-powered equipment
• LED drivers
• Distributed power systems
• Telecom power supplies
• Point-of-load converters

Electrical Characteristics

Absolute Maximum Ratings

• Input Voltage (VIN): -0.3V to +45V
• Switch Voltage (VSW): -0.3V to +65V
• Feedback Voltage (VFB): -0.3V to +5V
• Shutdown Pin Voltage: -0.3V to +40V
• Operating Junction Temperature: +150°C
• Storage Temperature Range: -65°C to +150°C

Recommended Operating Conditions

• Input Voltage Range: 4V to 40V
• Output Voltage Range: 1.23V to 60V (adjustable version)
• Operating Temperature Range: -40°C to +125°C
• Maximum Switch Current: 5A (peak)
• Oscillator Frequency: 52kHz (typical)

Electrical Specifications

(TA = 25°C, VIN = 12V, unless otherwise specified)

• Feedback Voltage: 1.23V ±2%
• Feedback Pin Bias Current: 50nA (typical)
• Switch Saturation Voltage: 1.5V (typical) at 3A
• Switch Leakage Current: 100μA (maximum)
• Shutdown Threshold Voltage: 1.5V (typical)
• Shutdown Pin Current: 50μA (typical)
• Soft-start Charge Current: 10μA (typical)
• Oscillator Frequency Variation: ±10% over temperature

Functional Description

Current Mode Control

The LM2588T ADJ employs current mode control, which offers several advantages over traditional voltage mode control. This architecture provides inherent line feedforward, resulting in excellent line transient response. The current mode approach also simplifies loop compensation while providing cycle-by-cycle current limiting for enhanced reliability.

Soft-start Function

The integrated soft-start feature gradually ramps up the output voltage during startup, preventing excessive inrush current that could stress components or cause input voltage droop. This controlled startup sequence is particularly valuable in systems with multiple power rails or sensitive downstream components.

Shutdown Function

The shutdown pin allows external control of the regulator's operation. Pulling this pin low (below 1.5V typical) disables the switching regulator, reducing input current to a minimal leakage level. This feature is useful for power sequencing or implementing standby modes in battery-powered applications.

Package Information

TO-220 Mechanical Data

• Package Type: TO-220-5 (5-pin)
• Mounting Style: Through-hole
• Lead Material: Copper alloy
• Lead Finish: Matte Tin
• Package Weight: 2.0g (typical)
• Package Dimensions: 10.0mm x 15.0mm x 4.5mm (body)
• Lead Pitch: 1.7mm
• Operating Temperature Range: -40°C to +125°C
• Thermal Resistance, Junction-to-Air: 62°C/W
• Thermal Resistance, Junction-to-Case: 5°C/W

Pin Configuration

• Pin 1: Feedback (FB) - Output voltage sense input
• Pin 2: Shutdown (SD) - Active-high shutdown control
• Pin 3: Switch (SW) - Collector of internal NPN switch
• Pin 4: Ground (GND) - Circuit ground reference
• Pin 5: Input (VIN) - Supply voltage input

Design Considerations

Output Voltage Programming

The adjustable version (LM2588T ADJ) uses an external resistor divider network to set the output voltage according to the formula: VOUT = 1.23V × (1 + R1/R2). For best performance, R2 should be in the range of 1kΩ to 10kΩ.

Inductor Selection

The inductor value affects both the output ripple and the converter's ability to maintain regulation. For most applications, an inductor value between 10μH and 100μH is appropriate. The inductor must be rated for the peak switch current (5A maximum) and have low DC resistance to minimize losses.

Thermal Management

Proper heat sinking is essential when operating at high input voltages or output currents. The TO-220 package allows for easy attachment of a heatsink. Forced air cooling may be necessary in high ambient temperature environments or when operating near maximum ratings.

Reliability and Compliance

• ESD Protection: Human Body Model ≥ 2kV
• RoHS Compliant: Yes
• Halogen Free: Yes
• MTBF: >1,000,000 hours (calculated)