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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 wanting to discuss a power supply circuit on a board under development.
Have you checked if the pin is available?
I heard that the DC/DC converter for the FPGA circuit is supported by our FAE and is working without any problems, but have you had any problems with the power supply circuit?
yes. Thanks to you, the FPGA circuit is working without any problems.
I'm not talking about power supply ICs today, but is that okay?
Yes, I will answer if it is something I know.
thank you.
Actually, I have a question about the microcontroller installed on the board along with the FPGA.
The microcontroller I'm using has a pin called INTVCC.
This is the 3.3V output pin of the regulator used inside the microcontroller, but this 3.3V is currently being used for an external small-scale logic circuit.
However, some boards do not output 3.3V properly, causing the microcontroller to malfunction.
Did the datasheet say that the INTVCC pin output 3.3V can also be used with external circuitry?
No, there was no description, but since it is several tens of mA, I thought there would be no problem and used it.
If it's not listed in the datasheet, don't use it.
However, I can't give up because it outputs 3.3V and I can save the cost of one regulator...
Why should I not use it?
Most internal regulators are intended to accommodate very small current values for bias circuits inside the IC.
In most cases, it is also difficult to operate logic circuits.
I think it would be a good idea to check with the manufacturer, but please don't get your hopes up as it is often not recommended.
･･･. Why do manufacturers provide output pins for power supplies that cannot be used?
Most of the reasons why the output of the internal regulator is output to the outside as an IC pin is to place a capacitor for noise reduction.
If you create a capacitor for noise removal internally, the silicon chip area will increase, which will increase costs.
We recommend that you do not use an internal regulator and instead install a dedicated power supply.
Is that so. We will put a dedicated power supply in the next revision.
The point of this time
The output pins of regulators for internal circuits often cannot be used as power supplies for external circuits. When considering use, be sure to check the product data sheet.
(Using it when it is not recommended may cause trouble. Please do not use it.)
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