TL494CN - Pulse Width Modulation Control Circuit

Overview

The TL494CN is a fixed-frequency pulse width modulation (PWM) control circuit designed for switching power supply applications. This integrated circuit incorporates all the essential building blocks required for precise power supply control, including an on-board oscillator, error amplifiers, a flip-flop control circuit, and output drivers. The device is widely used in DC-DC converters, power inverters, and other power management systems due to its reliability and flexibility.

Key to its operation is an internal linear sawtooth oscillator whose frequency can be programmed using two external components: a timing resistor (RT) and a timing capacitor (CT). The TL494CN offers push-pull or single-ended output configurations, making it adaptable to various power supply topologies.

Features

• Complete PWM Control Circuitry: Integrates all necessary functions for power supply control in a single package.
• Adjustable Oscillator Frequency: Programmable via external RT and CT components, typically ranging from 1kHz to 300kHz.
• Dual Error Amplifiers: Features two high-gain error amplifiers for voltage feedback and current limiting.
• Variable Dead-Time Control: Allows precise adjustment of output dead time to prevent shoot-through in half-bridge configurations.
• Output Configuration Options: Supports both push-pull and single-ended output modes.
• Internal Reference Voltage: Provides a stable 5V reference (±1% tolerance) for system use.
• Undervoltage Lockout: Ensures proper operation only when VCC is within specified range.
• Wide Operating Voltage Range: 7V to 40V operation with 200mA output sink/source capability.

Applications

The TL494CN is versatile and finds use in numerous power electronics applications:

• Switch-mode power supplies (SMPS)
• DC-DC converters and voltage regulators
• Uninterruptible power supplies (UPS)
• Power inverters and motor control circuits
• Battery chargers and solar power systems
• Industrial power control systems
• Computer peripheral power supplies

Electrical Characteristics

Absolute Maximum Ratings

• Supply Voltage (VCC): 41V
• Collector Output Voltage: 41V
• Collector Output Current: 250mA
• Amplifier Input Voltage: -0.3V to VCC
• Power Dissipation: 1000mW
• Operating Junction Temperature: -40°C to +125°C
• Storage Temperature Range: -65°C to +150°C

Recommended Operating Conditions

• Supply Voltage (VCC): 7V to 40V
• Oscillator Frequency Range: 1kHz to 300kHz
• Timing Capacitor (CT): 0.47nF to 10µF
• Timing Resistor (RT): 1.8kΩ to 500kΩ
• Operating Temperature Range: 0°C to 70°C (commercial)

Electrical Specifications (at TA = 25°C, VCC = 15V)

• Reference Output Voltage: 4.95V to 5.05V
• Reference Load Regulation: 5mV (0mA to 10mA)
• Oscillator Frequency Variation: ±10% (over temperature)
• Error Amplifier Input Offset Voltage: ±2mV (max)
• Error Amplifier Input Bias Current: 0.2µA (typ)
• Output Saturation Voltage: 1.1V (Isink = 200mA)
• Standby Supply Current: 10mA (max)

Package Information

The TL494CN is available in a standard 16-pin plastic dual in-line package (PDIP):

• Package Type: PDIP-16
• Dimensions: 19.3mm x 6.35mm x 4.57mm (body)
• Pin Spacing: 2.54mm (100 mil) pitch
• Lead Material: Copper alloy
• Lead Finish: Matte tin
• Moisture Sensitivity Level (MSL): MSL 1 (unlimited floor life)
• RoHS Compliance: Yes

Pin Configuration

• Pin 1: Non-inverting input (Error Amp 1)
• Pin 2: Inverting input (Error Amp 1)
• Pin 3: Feedback/Compensation/PWM comparator input
• Pin 4: Dead-time control input
• Pin 5: CT (Timing capacitor)
• Pin 6: RT (Timing resistor)
• Pin 7: Ground
• Pin 8: Collector (Output transistor 1)
• Pin 9: Emitter (Output transistor 1)
• Pin 10: Emitter (Output transistor 2)
• Pin 11: Collector (Output transistor 2)
• Pin 12: VCC (Supply voltage)
• Pin 13: Output control (Push-pull/single-ended select)
• Pin 14: Reference output (5V)
• Pin 15: Inverting input (Error Amp 2)
• Pin 16: Non-inverting input (Error Amp 2)

Functional Description

The TL494CN operates by comparing the sawtooth waveform from its internal oscillator with control signals from its error amplifiers to generate PWM signals. The dead time control feature prevents simultaneous conduction of output transistors in push-pull configurations. The device offers excellent noise immunity and stability through its fully compensated error amplifiers.

The output stage can be configured for either push-pull operation (where outputs are 180° out of phase) or single-ended operation (where outputs operate in parallel). This flexibility allows the TL494CN to drive various power stage configurations including half-bridge, full-bridge, and forward converter topologies.

Design Considerations

When designing with the TL494CN, several factors should be considered:

• Proper selection of RT and CT values to achieve desired switching frequency
• Adequate decoupling of VCC and reference voltage pins
• Proper heat sinking if operating at high ambient temperatures
• Careful PCB layout to minimize noise coupling to sensitive control inputs
• Appropriate gate drive circuitry when using external power MOSFETs
• Proper compensation of error amplifiers for stable feedback loops