UC3525A PWM Controller Technical Summary

Overview

The UC3525A is a monolithic integrated circuit designed to provide all the necessary control functions for pulse width modulation (PWM) in switching regulator applications. This highly versatile IC incorporates multiple critical components including a precision voltage reference, error amplifier, PWM comparator, oscillator, under-voltage lockout protection, soft-start circuitry, and high-current output drivers. Packaged in a 16-pin DIP configuration, the UC3525A is particularly well-suited for switch-mode power supply (SMPS) designs requiring robust performance and flexible control features.

Key Features

• Precision Voltage Reference: 5V ±1% accuracy for stable regulation
• Synchronizable Oscillator: External sync capability via dedicated terminal
• Programmable Soft-Start: Internal soft-start circuit for controlled startup
• Adjustable Deadtime Control: Precise deadtime adjustment between outputs
• Robust Protection: Under-voltage lockout (UVLO) for supply protection
• High Current Output: 500mA peak output current capability
• Wide Operating Range: -30°C to +85°C temperature range
• Dual Output Drivers: Push-pull outputs for flexible power stage control

Applications

The UC3525A finds application in a wide variety of power conversion systems, including:

• Switch-mode power supplies (forward, flyback, push-pull topologies)
• DC-DC converters and voltage regulators
• Uninterruptible power supplies (UPS)
• Motor control systems
• Inverter and power amplifier systems
• Industrial power control equipment
• Telecommunications power systems

Electrical Characteristics

All specifications are given for V_CC = 20V and operating temperature range of -30°C to +85°C unless otherwise noted.

Absolute Maximum Ratings

• Supply Voltage (V_CC): 40V
• Collector Supply Voltage (V_C): 40V
• Output Current (Sink or Source): 500mA
• Reference Output Current: 50mA
• Error Amp Input Voltage Range: -0.3V to V_CC
• Power Dissipation: 1000mW
• Operating Junction Temperature: +150°C
• Storage Temperature Range: -65°C to +150°C

Recommended Operating Conditions

• Supply Voltage Range: 8V to 35V
• Oscillator Frequency Range: 100Hz to 500kHz
• Deadtime Control Range: 0% to 100%
• Soft-Start Capacitor Range: 0.1µF to 100µF
• Timing Capacitor Range: 0.001µF to 0.2µF
• Timing Resistor Range: 2kΩ to 150kΩ

Electrical Specifications

• Reference Voltage: 5V ±1% (over line and load)
• Reference Load Regulation: 20mV (0mA to 20mA)
• Error Amp Input Offset Voltage: 2mV (max)
• Error Amp Gain Bandwidth: 3MHz (typ)
• Oscillator Frequency Accuracy: ±6% (over temperature)
• Output Rise/Fall Time: 50ns (with 1nF load)
• Under-Voltage Lockout Threshold: 7V (on), 6.5V (off)
• Quiescent Supply Current: 15mA (typ)

Package Information

16-Pin DIP Package Details

• Package Type: PDIP-16 (Plastic Dual In-line Package)
• Dimensions: 19.3mm x 6.35mm (body)
• Pin Spacing: 2.54mm (standard DIP pitch)
• Lead Material: Copper alloy
• Lead Finish: Matte tin
• Mounting Style: Through-hole
• Operating Temperature: -30°C to +85°C

Pin Configuration

• Pin 1: Inverting Input (Error Amp)
• Pin 2: Non-Inverting Input (Error Amp)
• Pin 3: Sync (Oscillator Synchronization)
• Pin 4: Oscillator Output
• Pin 5: CT (Timing Capacitor)
• Pin 6: RT (Timing Resistor)
• Pin 7: Discharge
• Pin 8: Soft-Start
• Pin 9: Compensation
• Pin 10: Shutdown
• Pin 11: Output A
• Pin 12: Ground
• Pin 13: V_C (Collector Supply)
• Pin 14: Output B
• Pin 15: V_CC (Supply Voltage)
• Pin 16: V_REF (5V Reference)

Functional Description

The UC3525A integrates all the essential building blocks for a complete PWM control solution. The internal 5V reference provides a stable voltage for feedback networks and other circuitry. The error amplifier compares the feedback signal with the reference to generate an error signal that modulates the pulse width. The oscillator generates the switching frequency, which can be synchronized to an external clock if needed. The PWM comparator translates the error signal into a variable duty cycle. The under-voltage lockout ensures proper operation only when the supply voltage is sufficient, while the soft-start feature gradually increases the duty cycle during startup to prevent current surges.

Internal Block Diagram Overview

The IC's architecture includes the following functional blocks:

• Bandgap voltage reference
• High-gain error amplifier
• Precision oscillator with sync capability
• PWM comparator with latch
• Deadtime control comparator
• Soft-start circuitry
• Under-voltage lockout
• Dual totem-pole output drivers
• Output flip-flop for alternating outputs

Design Considerations

When implementing the UC3525A in power supply designs, several factors