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Honored ContributorUsing LM317 to power FPGA
Analysing a couple of schematics I found out some using this device. Declared input voltage is 5..9v. Research of datasheet for LM317 shows that Vin-Vout should be >3v. Thus it will not be possible to make 3v3 from 5v. Am I correct? Anyone has experience with it and can prove/disprove it?
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Altera_ForumCurrent consumption depends mainly on the actual amount of switching registers and logic cells. It can't be estimated without analyzing the design.
- Altera_Forum--- Quote Start --- Yes. Typical dropout is around 1.1 V. --- Quote End --- Cool, thanks. Will supplied current (1A) be enough? I was trying to run Altera's power calculation spreadsheet, but do not understand how to use it... So can not answer this question myself. Q240, in max config all pins are used bi-directionally, half of CLKs are used, reference frequency is 50MHz. Can you give any estimation on the power consumption on 3v3 power rail?
- Altera_Forum
Yes. Typical dropout is around 1.1 V.
- Altera_Forum--- Quote Start --- There's a dropout voltage diagram in the datasheet. It clarifies that 1.7 V differential is too low if the input voltage is as low as 5V. 6V input voltage (actual minimumm, considering voltage ripple!) would be O.K. You should use a typical LDO regulator. --- Quote End --- Thank you for reply. Will LM1117-3.3 help? It seems to have 1.5v dropout. However it has 800ma...1A current rating...
- Altera_Forum
There's a dropout voltage diagram in the datasheet. It clarifies that 1.7 V differential is too low if the input voltage is as low as 5V. 6V input voltage (actual minimumm, considering voltage ripple!) would be O.K. You should use a typical LDO regulator.
