Narrow down by specifying conditions
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This is Sasaki in charge of power supply dock technology.
In this column, I would like to introduce some examples of problems related to power supplies that I encountered multiple times during various customer support sessions.
We received an inquiry from a customer about designing a power supply circuit for FPGA core voltage.
Relationship between power supply output accuracy and voltage dividing resistor accuracy
I was in charge of board design for the first time, and I was reviewing the power supply circuit and voltage accuracy of the FPGA core.
Is the accuracy of the reference voltage of the power supply IC not good?
No, the reference voltage accuracy is 1%.
You have selected a high-precision power supply IC. If so, I don't think it's a problem.
That's right...
Is there anything you don't understand?
In fact, I'm using 1% precision resistors as the voltage dividing resistors that determine the output voltage, but in that case, using two resistors would result in an error of +/-1% and a maximum of 2%, right?
A 1% deviation in the reference voltage results in a maximum of 3%, which is 1.0V x 3% = 30mV. . .
It's fine as it is now.
If you calculate properly, you can confirm that the voltage accuracy is within ±30mV.
e? ! really? !
When using the E96 series resistors, the value of the output voltage set by the voltage divider resistors of 301KΩ and 75KΩ is 0.9993V.
Using +1% and -1% error resistors gives 0.99538V, a 4.6mV error over 1V.
How to calculate voltage
That's right!
Then add 10mV of 1% error of the reference voltage to this error and
Variation including temperature characteristics, line regulation, and load regulation are taken into account.
If the selected device is within 30mV, you should be fine.
Thank you very much. relieved.
By the way, what are line regulation and road regulation?
There is an explanation in the FAQ, so please refer to it.
Yes, I understand. Oh, was it possible to use our company's E96 series resistors?
Please do your best to negotiate so that it can be used, or use multiple resistors to successfully drive the center value of the voltage to 1.0 V (laughs).
I understand. I will do my best! !
The point of this time
It is important to check by hand calculation instead of judging by feeling.
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