The Ultimate Guide to TL494 Current-Mode PWM Controller IC

Are you an engineer or designer searching for an optimal method to manage the amplitude of digital signals? Your project may involve controlling electrically powered devices, and you may lack expertise in this domain. Your quest concludes here as we present the solution. The TL494 PWM controller is the ideal choice. The TL494 is a multifaceted PWM control integrated circuit (IC) that can be employed in various electronic circuit applications. The TL494 PWM controller also encompasses all essential features, empowering you to build a practical PWM control circuit.

In this article, we will explore TL494, from its features, pinout, and datasheet to its working, applications, how to use it in practical circuits and more details.

What is TL494 PWM Controller?

The TL494 IC is a current-mode PWM controller with a fixed frequency, encompassing all the essential features required to construct a pulse-width modulation (PWM) control circuit on a single chip. Its primary design focus is SWITCHMODE power supply control.

This versatile device integrates the necessary functions for building a PWM control circuit on a single chip, tailored primarily for power-supply control applications. The TL494 offers flexibility in adapting power-supply control circuitry to specific applications.

Key features of the TL494 include two error amplifiers, an on-chip adjustable oscillator, a dead-time control (DTC) comparator, a pulse-steering control flip-flop, a 5V, 5%-precision regulator, and output-control circuits.

The error amplifiers feature a common-mode voltage range from –0.3V to VCC – 2V. The dead-time control comparator includes a fixed offset, providing approximately 5% dead time. The on-chip oscillator can either be bypassed or utilized to drive common circuits in synchronous multiple-rail power supplies, depending on whether RT is terminated to the reference output and a sawtooth input is provided to CT.

The uncommitted output transistors offer both common-emitter and emitter-follower output capabilities. The TL494 allows push-pull or single-ended output operation, with the output-control function facilitating the selection between these modes. The device's architecture ensures that neither output is pulsed twice during push-pull operation.

TL494 Pinout

The pin diagram and pin details for the TL494 are presented below. The explanation provides fundamental information regarding the pin functions of the TL494 IC.

TL494 pin diagram

Pinout Configuration

Pin No.	Pin Name	Description
1	1IN+	Noninverting input to error amplifier 1
2	1IN-	Inverting input to error amplifier 1
3	FEEDBACK	Input pin for feedback
4	DTC	Dead-time control comparator input
5	CT	Capacitor terminal used to set the   oscillator frequency
6	RT	Resistor terminal used to set the   oscillator frequency
7	GND	Ground Pin
8	C1	The collector terminal of BJT output 1
9	E1	The emitter terminal of BJT output 1
10	E2	The emitter terminal of BJT output 2
11	C2	The collector terminal of BJT output 2
12	VCC	Positive Supply
13	OUTPUT CTRL	Selects single-ended/parallel output or   push-pull operation
14	REF	The 5-V reference regulator output
15	2IN-	Inverting input to error amplifier 2
16	2IN+	Noninverting input to error amplifier 2

Internal Structure

Now, let's delve into the various components comprising the internal structure of the TL494.

5V Reference Source

The TL494 features a built-in reference source based on the bandgap principle, providing a stable 5V output voltage. However, there's a requirement – the VCC voltage needs to exceed 7V with an error within 100mV. The 14th pin, REF, serves as the output pin for the reference source per the pin configuration table.

Operational Amplifier

The TL494 incorporates two operational amplifiers powered by a single power supply. The operational amplifiers feature a transfer function given by ft(ni, inv) = A(ni-inv), with the constraint that this transfer function does not surpass the output swing.

Each operational amplifier provides an output terminal that can be linked to a diode. The diode acts as a connection between the op-amps and the subsequent circuit. When connected to the COMP pin, the diode ensures that the op-amp with the higher output feeds into the subsequent circuit.

Sawtooth Oscillator

One of the key features contributing to the popularity of the TL494 is its integrated sawtooth wave oscillator. This oscillator produces a sawtooth wave ranging from 0.3 to 3V. Additionally, you can modify the oscillation frequency by incorporating an external resistor (Rt) and capacitor (Ct). The default oscillation frequency can be expressed as f = 1/(Rt*Ct).

Here, the unit of Ct is farads, and Rt is measured in ohms.

Pulse Trigger

The primary function of the pulse flip-flop is to activate during the descending edge of both the comparator output and the sawtooth wave. Consequently, one of the output switches is activated. Subsequently, it deactivates when the comparator output returns to zero.

Comparator

The subsequent circuit mentioned earlier is the comparator. In this setup, the signal output from the operational amplifier (COMP pin) is directed to the positive input terminal of the comparator.

The comparator assesses the sawtooth wave received from the negative input terminal against the COMP pin within the chip. In other words, if the sawtooth wave is higher, the comparator produces a zero output. Otherwise, it produces a one.

Quiet Time Comparator

Pin 4, the dead-time control (DTC) pin, configures the dead-zone time. It employs the dead-time comparator to influence the pulse and restrict the maximum duty cycle. This allows you to establish an upper limit for all duty cycles, typically set at 45%. However, when the DTC pin level is at zero, the upper limit of the duty cycle is approximately 42%.

Error Amplifiers

You can bias the two error amplifiers using the IC's supply rail. This biasing results in the error amplifiers obtaining a high gain, allowing for a common-mode input range from -0.3 V to 2 V less than V1.

The configurations of the error amplifiers function akin to single-supply amplifiers. Consequently, all outputs will possess only active-high capabilities. This setup enables the amplifiers to activate independently to meet the PWM requirements and provide a consistent current.

Output-Control Input

You can set the IC output pin to either single-ended or push-pull mode. In the single-ended mode, both outputs oscillate simultaneously in parallel. Conversely, the push-pull mode generates alternating oscillating outputs.

The output-control pin directly governs the IC's output without impacting the flip-flop pulse-steering or internal oscillator stage.

Output Transistors

The output transistor comprises a collector terminal and an uncommitted emitter. These two terminals can accept (sink) or provide (source) a current of up to 200 mA.

When you set the saturation point of the transistors in the common-emitter mode, it becomes less than 1.3 V. Additionally, it's also less than 2.5 V when configured in a common-collector manner.

Features & Specifications

Features:

• Built-in PWM Control ChannelComprehensive Pulse Width Modulation Control Circuitry

• Comprehensive Pulse Width Modulation Control Circuitry

• On-chip oscillator with Master or Slave Operation

• The TL494 incorporates a variable-range dead-time control feature

• Easy synchronization with other circuits

• Two PWM outputs

• Fixed frequency oscillator included

• On-Chip Error Amplifiers

• On-Chip 5.0 V Reference

• Adjustable Dead-time Control

• Uncommitted Output Transistors Rated up to 500 mA Source or Sink

• Dual output selectable operations with Output Control for Push−Pull or Single−Ended Operation

• Undervoltage Lockout

• NCV Prefix for Automotive and Other Applications Requiring Site and Control Changes

• Pb−Free Packages are Available

Specifications:

• Operating Voltage Range: 7V to 40V

• Number of Outputs: 2 Output

• Switching Frequency: 300 kHz

• Maximum Duty Cycle: 45%

• Output Voltage: 40 V

• Output Current: 200 mA

• Maximum Output Current for Both PWMs: 250 mA

• Temperature Range: -65 to 150 degrees

• Fall Time: 40 ns

• Rise Time: 100 ns

• Available in 16-pin PDIP, TSSOP, SOIC, and SOP Packages

Absolute Maximum Ratings

• (VCC) Ensure the Maximum Supply Voltage does not exceed 41 V.

• (VI) Ensure the Maximum Voltage on input pins does not exceed VCC + 0.3 V.

• (VO) Ensure the Maximum Output Voltage at the collector of the internal transistor is 41 V.

• (IO) Ensure the Maximum Current on the collector of the internal transistor is 250 mA.

• Ensure the Maximum IC Pin Soldering Heat at 1.6 mm (1/16 inch) away from the IC body does not exceed 10 seconds @ 260 °C.

• Storage Temperature Range (Tstg): –65/150 °C.

Recommended Operating Conditions

The provided information outlines the recommended voltages and currents for the safe and efficient operation of the IC:

• VCC Supply Voltage: 7 V to 40 V

• VI Amplifier Input Voltage: -0.3 V to VCC - 2 V

• VO Transistor Collector Voltage: 40 V, Collector Current for each Transistor: 200 mA

• Current into Feedback Pin: 0.3 mA

• fOSC Oscillator Frequency Range: 1 kHz to 300 kHz

• CT Oscillator Timing Capacitor Value: Between 0.47 nF to 10000 nF

• RT Oscillator Timing Resistor Value: Between 1.8 k to 500 k Ohms.

How does the PWM Controller Work?

As mentioned, the TL494 operates as a dual PWM control circuit with a fixed frequency and variable duty cycle. It functions without external components, relying only on a few resistors and capacitors for oscillator operation. The oscillator generates a sawtooth waveform based on the timing capacitor CT. The TL494 generates signals by comparing the sawtooth waveform with two control signals from the error amplifiers. As illustrated in the block diagram above, the output signal is active when the sawtooth voltage exceeds the voltage at the error amplifiers' outputs.

• Output Signal Low: Sawtooth voltage is less than the control signal voltage.

• Output Signal High: Sawtooth voltage is greater than the control signal voltage.

The PWM output signal is transferred to the output transistors through the Pulse-Steering Flip-Flop.

How to Select Oscillator Frequency?

In the preceding section, we observed that the oscillator plays a crucial role in generating the sawtooth waveform. This waveform is utilized for both dead-time control and PWM comparator amplifiers. Consequently, the oscillator frequency dictates the frequency of the output signals. Let's delve into the process of choosing the oscillator frequency.

The frequency can be tailored by choosing appropriate RT resistor and CT capacitor values. The selection of capacitor and resistor values aligns with the following formula:

Frequency= 1/ RT X CT

Where to Use TL494?

Irrespective of whether it's employed in a buck or boost topology, the TL494 fixed-frequency PWM Controller proves versatile for DC to DC conversion. It can maintain a constant current by adjusting the output voltage to the load. This IC encompasses an output control circuit, a flip-flop, a dead-time comparator, two error amplifiers, a 5V reference voltage, an oscillator, and a PWM comparator.

Therefore, if you seek an IC capable of generating PWM signals to regulate a power switch based on the circuit's current, this IC would be a suitable choice.

How to Use TL494?

Ground is connected to the inverting pins, while the non-inverting pins are linked to the Ref pin. The DTC and FEEDBACK pins receive test inputs. Pins 5 and 6, connected to an external capacitor and resistor, control the oscillator frequency. The error amplifier compares a sample of the 5-V output to the reference, adjusting the PWM to ensure a steady output current. The test circuit for the TL494 is depicted below.

TL494 Application

• Personal Computers

• Kitchen Microwave Appliances

• Power Supplies for Server Units

• Micro-Inverters for Solar Applications

• Washing Machines: Basic and High-End Models

• Electric Bicycles

• Devices for Smoke Detection

• Inverters for Solar Power Systems

• Power Supply Units: Alternating Current/Direct Current, Isolated, With Power Factor Correction, > 90 Watts

• Power Solutions for Telecommunications/Server Alternating Current/Direct Current Supplies: Dual Controller, Analog

Application Circuits Examples

As detailed earlier, the TL494 functions primarily as a PWM controller IC, making it most suitable for applications involving PWM-based circuits.

Below, we discuss a few example circuits that can be adapted and modified according to specific individual requirements.

TL494 Solar Charger

The provided design illustrates a practical configuration of the TL494 to establish a 5V/10A switching buck power supply.

In this setup, the output operates in parallel mode, as evident from the connection of the output-control pin#13 to the ground.

Both error amplifiers are utilized efficiently in this configuration. The first error amplifier regulates voltage feedback through R8/R9, ensuring a constant output at the desired rate (5V).

The second error amplifier is employed to control the maximum current via R13.

TL494 Classic Inverter Circuit

Presented is a traditional inverter circuit constructed using the TL494 IC. In this instance, the output is set up to operate in a push-pull manner, leading to the connection of the output-control pin with the +5V reference derived from pin #14. The remaining pins are configured precisely as detailed in the datasheet above.

TL494 Circuit Diagram

TL494 Circuit Diagram

TL494 Timing Diagram

TL494 Equivalent & Alternatives

The equivalents for TL494 are UC3843 and TL3842.

Alternative PWM controller ICs for TL494 are UC2842 and SG2524.

TL494 Package

TL494 Datasheet

Download TL494 Datasheet PDF.

Final Words

In general, the TL494 IC is a pulse-width modulation (PWM) control IC equipped with exact output and feedback control features, making it well-suited for various PWM circuit applications. Furthermore, the TL494 shares similarities with the SG3525 and can be an alternative. It is essential to highlight that these two ICs are not interchangeable due to differences in their pin configurations.

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