TL494CN PWM Controller: Pin Configuration, Layout Guidelines and Working Principle
26 October 2023
Ⅰ. Overview of TL494CN PWM controller
Ⅱ. Symbol, footprint and pin configuration of TL494CN PWM controller
Ⅲ. Technical parameters of TL494CN PWM controller
Ⅳ. What are the features of TL494CN PWM controller?
Ⅴ. Layout guidelines for TL494CN PWM controller
Ⅵ. Absolute maximum ratings of TL494CN PWM controller
Ⅶ. How does the TL494CN PWM controller work?
Ⅷ. What are the applications of TL494CN PWM controller?
TL494CN is a fixed frequency pulse width modulation circuit with all the functions required for switching power supply control. It finds extensive application in half-bridge, full-bridge, and single-ended forward dual-tube switching power systems. It contains all necessary functions for power control, enabling power control circuits to be customized for specific applications.
It provides two PWM outputs, each capable of delivering currents up to 200mA, rendering it versatile for a wide range of applications. In addition, it features a switching frequency of 300 kHz, ensuring efficient and precise control over connected devices. Moreover, the device's sturdy construction enables seamless operation across an extensive temperature spectrum, from -40°C to 85 °C, suitable for extreme cold and hot environments. Regarding power supply, it supports a minimum operating voltage of 7V and can handle a maximum operating voltage of 40V, offering flexibility and adaptability for a variety of power sources.
Replacement and equivalent:
• SG3525
• TL494CDR
• UC3843
TNY268PN has a total of 16 pins. Its pin names and descriptions are as follows:
Pin 1 (1IN+): Input 1 for error amplifier one (Non-Inverting)
Pin 2 (1IN-): Input 2 for error amplifier one (Inverting)
Pin 3 (FEEDBACK): Feedback connection pin from outputs
Pin 4 (DTC): Input for dead-time control comparator
Pin 5 (CT): Capacitor terminal to set frequency
Pin 6 (RT): Resistor terminal to set frequency
Pin 7 (GND): Ground pin for power supply
Pin 8 (C1): Collector pin of Output 1
Pin 9 (E1): Emitter pin of Output 1
Pin 10 (E2): Emitter pin of Output 2
Pin 11 (C2): Collector pin of Output 2
Pin 12 (VCC): Positive Power supply pin
Pin 13 (OUTPUT CTRL): Select output mode from three options
Pin 14 (REF): Reference for 5 volts regulator
Pin 15 (2IN-): Input 1 for error amplifier two (Inverting)
Pin 16 (2IN+): Input 1 for error amplifier two (Non-Inverting)
• It incorporates an integrated error amplifier to compare and boost the input signal for achieving precise control.
• It has a built-in high-performance internal voltage regulator that can provide a stable 5V reference power supply with a 5% tolerance.
• It is a switching power supply controller with a built-in power transistor, with push or pull output modes, and can provide a driving capability of up to 500mA.
• The TL494CN features an integrated standalone sawtooth wave oscillator, where the frequency is determined by an RC timing circuit. You can calculate the oscillation frequency using the formula: fo (kHz) = (1.2) / (R in kΩ) * (C in μF), where R denotes the resistance value, and C denotes the capacitance value. Notably, this circuit can achieve a maximum oscillation frequency of up to 300kHz.
• Adjustable dead time
• Complete PWM power control circuit
• The chip has a built-in linear sawtooth oscillator and only two external oscillator components (resistance and capacitor).
• Integrated all pulse width modulation circuits
• It is specially designed for driving bipolar switching tubes. Although most devices currently use MOSFET switching tubes, they usually require external sinking circuits to work, and this circuit is where TL494CN is widely used.
1. Compensation Components
To ensure stability, it is advisable to position external compensation elements near the IC. Surface mount components are also a preferred choice for the same reasons mentioned earlier in the context of filter capacitors. However, it's important to note that these components should not be situated in close proximity to the inductor.
2. Traces and Ground Planes
Optimize the high-current power traces on your PCB for minimal length, directness, and thickness. It's advisable to ensure that traces on a standard PCB are at least 15 mils (0.381 mm) wide per Ampere.
The inductor, output capacitors, and output diode should be positioned as close to each other as feasibly achievable. This proximity minimizes electromagnetic interference radiated by the power traces resulting from the high switching currents. Additionally, this arrangement diminishes lead inductance and resistance, thereby reducing noise spikes, ringing, and resistive losses that can lead to voltage errors.
Connect the LC grounds, input capacitors, output capacitors, and, if applicable, the output diode in close proximity to a ground plane. It's advisable to implement ground planes on both sides of the PCB for noise reduction by minimizing ground loop errors and increasing absorption of electromagnetic radiation emitted by the inductor.
For multi-ayer boards with more than two layers, a ground plane can be used to separate the power plane (where the power traces and components are) and the signal plane (where the feedback and compensationand components are) for improved performance.
On multi-layer boards the use of vias will be required to connect traces and different planes.
lt is good practice to use one standard via per 200 mA of current if the trace will need to conduct a significant amount of current from one plane to the other.
Organize the components in such a way that the switching current loops consistently flow in the same direction. Given the operational principles of switching regulators, there exist two distinct power states: one when the switch is active and another when it is inactive. In each of these states, the power components conducting the current create specific loops. Position the power components to ensure that in both of these states, the current flows in a uniform direction. This preventive measure safeguards against magnetic field reversal due to the connections between the two half-cycles and minimizes emitted electromagnetic interference (EMI).
3. Feedback Traces
Try to run the feedback trace as far from the inductor and noisy power traces as possible. You would also likethe feedback trace to be as direct as possible and somewhat thick. These two sometimes involve a trade-off, but keeping it away from inductor EMl and other noise sources is the more critical of the two. Run the feedback trace on the side of the PCB opposite of the inductor with a ground plane separating the two.
4. Input/Output Capacitors
When employing a low-value ceramic input filter capacitor, it's essential to position it in immediate proximity to the VCC pin of the IC. This placement minimizes trace inductance effects and ensures a cleaner voltage supply for the internal IC rail. In certain designs, a feed-forward capacitor may be necessary, typically connected from the output to the feedback pin for stability considerations. In such instances, it should likewise be located as close to the IC as feasible. Employing surface mount capacitors additionally reduces lead length and mitigates the risk of noise interference, particularly when compared to through-hole components, which can inadvertently act as antennas.
Over operating free-air temperature range (unless otherwise noted)
TL494CN is a fixed frequency pulse width modulation circuit with built-in linear sawtooth oscillator. It allows for adjustment of the oscillation frequency using external resistors and capacitors. By comparing the pulse from the output capacitor with two other control signals via the positive sawtooth voltage on the capacitor, it enables control of power output transistors Q1 and Q2 through a NOR gate. The flip-flop, on the other hand, will only transmit the signal when the clock signal is in a low state, effectively gating the signal during periods when the sawtooth voltage surpasses the control signal duration. As the control signal amplitude increases, the width of the output pulse gradually diminishes.
TL494CN is widely used in the following fields:
• Electric bicycle
• Micro-wave oven
• Smoke detectors
• Server power supply
• Desktop computer
• Solar inverters
• Solar microinverter
Frequently Asked Questions
1. What is the use of TL494CN?
TL494CN can be used to provide a constant current by varying the output voltage to the load. This IC feature an output control circuit, a flip flop, a dead time comparator, two different error amplifiers, a 5V reference voltage, an oscillator, and a PWM comparator.
2. What are the protection features of TL494CN?
TL494CN usually has functions such as over-current protection, over-temperature protection and short-circuit protection. These protective features help protect circuits from faults and overloads.
3. What is the operating temperature range of TL494CN?
The operating temperature of TL494CN ranges from -40°C to 85 °C.
4. What are the typical applications of the TL494CN?
Typical applications include switched-mode power supplies (SMPS), inverters, motor control, lighting control, and other systems requiring PWM control.
5. How does TL494CN work?
The TL494CN is a fixed-frequency pulse-width-modulation (PWM) control circuit. Modulation of output pulses is accomplished by comparing the sawtooth waveform created by the internal oscillator on the timing capacitor (CT) to either of two control signals.
