I want to make a voltage down converter to power my controller (Atmega328P).
Input = 12V / Output = 5V (3A). As a converter, I use ST1S40.
My connection diagram
I took the circuit from datasheet, changed the values of resistors R1, R2. The rest is unchanged. I did not find the connection scheme of this converter with an output voltage of + 5V.
Why did I choose him? To connect it does not require a lot of components. Unfortunately, I did not find other options.
Answer
If you want a 5 volt output then you need to recalculate R1 and R2. At the moment it will regulate to 6.8 volts and not 5 volts. This is because the FB pin needs to "see" 0.8 volts and with 5 volts at the output, it will see 0.588 volts and, as a result, the duty cycle will increase until it sees 0.8 volts and that occurs when Vout = 6.8 volts.
As others have mentioned in comments you need to have the enable input pulled high.
You also need to ensure that the thermal pad beneath your chip is connected to ground and that you have applied enough copper on the PCB to ensure the junction temperature does not exceed 150 degC. Read section 6.4 of the data sheet.
Section 6.5 also draws your attention to correct PCB layout and, at the bottom also reminds you about the thermal pad: -
Thanks to the exposed pad of the device, the ground plane helps to reduce the thermal resistance junction to ambient; so a large ground plane, soldered to the exposed pad, enhances the thermal performance of the converter allowing high power conversion.
No comments:
Post a Comment