Understanding and learning to use the TL494

Understanding and learning to use the TL494.

TL494 is a versatile PWM controller IC. In this application note we will understand and know more about the

· Basic building blocks of TL494

· Details of each pin of TL494

· Basic circuit configuration for TL494

Basic building blocks

We will first start with understanding the building blocks of the TL494. This mainly consists of two error amplifiers, an oscillator, PWM comparator, a stable 5V reference generator and the output driving stage.

The block diagram is shown below

Pin Details

We will now take a look on each pin of TL494.

Pin#1 and Pin#2 (1 IN+ and 1IN-) : These are the non-inverting and inverting inputs of the error amplifier (op amp 1). These are mainly used to control the voltage in a converter circuit.

Pin#16, Pin#15 (1 IN+ and 1IN-) : As above, these are the non-inverting and inverting inputs of the error amplifier (op amp 2). And these are used mainly to control the current in the converter circuit.

Pin#8 and Pin#11 (C1, C2): These are the outputs 1 and 2 of the IC which are connected with the collectors of the respective internal transistors. If we are using a single converter configuration then we connect these two pins to a single point.

Pin#5 (CT): This pin needs to be connected with an external capacitor for setting the oscillator frequency. Its value should be kept between 0.47 nF to 10000 nF and should be a non-polar type capacitor.

Pin#6 (RT): This pin needs to be connected with an external resistor for setting the oscillator frequency. Its value should be kept between 1.8 k to 500 k Ohms.

Pin#4 (DTC): It's the input of the internal op amp which controls the dead-time operation of the IC. Dead time is the time for which the output is zero or you can say that the PWM duty cycle is zero. The dead time is necessary in the converter configurations like push-pull, half bridge and full bridge etc as this prevents the damage of transistors.

Pin#9 and Pin#10 (E1 and E2): These are the outputs of the IC which are connected with emitter pins of the internal transistor. In normal configuration these pins are grounded.

Pin#3 (Feedback): This is the feedback pin and is mainly used for frequency compensation of the converters.

Pin#7 (Ground): This pin is the ground pin of the IC, which needs to connect with the 0 V of the supply source.

Pin#12 (VCC): This is the positive supply pin of the IC.

Pin#13 (O/P CNTRL): This pin can be configured for enabling the output of the IC in the push-pull mode or single ended mode. If this pin connected to the REF pin then it enables the pus pull mode and if it is connected to ground then the single ended mode is activated.

Pin#14 (REF): This output pin provides a constant 5V output which can be used for fixing a reference voltage for the error op amps, in the comparator mode.

 

Absolute Maximum Ratings

Now we will look at the absolute maximum rating for this device. These are those limits, crossing which the device is damaged.

(VCC) Maximum Supply voltage not to exceed = 41 V

(VI) Maximum Voltage on input pins not to exceed = VCC + 0.3 V

(VO) Maximum output voltage at collector of internal transistor = 41 V

(IO) Maximum current on Collector of the internal transistor = 250 mA

Maximum IC pin soldering heat at 1.6 mm (1/16 inch) away from IC body not to exceed 10 seconds @ 260 °C

Tstg Storage temperature range = –65/150 °C

 

Recommended Operating Conditions

The following data gives you the recommended voltages and currents that can be used for operating the IC under safe and efficient conditions:

VCC supply: 7 V to 40 V

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

VO Transistor Collector Voltage = 40, 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.

 

Application circuit

Now as we have understood the details of the IC, it’s now time for the application circuit.

Below is the application circuit based on TL494. This circuit converts 32V DC to 5V DC at 10A.

The complete circuit calculations will be shown in next post.

The datasheet for this device can be downloaded from https://www.ti.com/lit/gpn/tl494

Courtesy- www.ti.com

Author- Aniruddh for Ani-Lab.