Sorry for my English at first.
Initially I implemented work with usb under this application circuit:
![Image]()
.
Controller - Attiny85 without crystal, on the PLL. And it worked perfectly.
Once, the supply voltage was 3.7V instead of 3.3V. Then I replaced the diodes with voltage regulator.
So the scheme was as follows:
![Image]()
And usb stopped working. (Invalid USB device, Windows said)
Other functions of the scheme still work.
According to datasheet, Attiny85 can not keep the requested frequency of 16.5 MHz at 3.3 volts. And I lowered the frequency to 12.8 MHz. But it did not help. Scheme with diodes works on 12,8 mhz too.
Why this difference of 0.4 volts so important?
Initially I implemented work with usb under this application circuit:
. Controller - Attiny85 without crystal, on the PLL. And it worked perfectly.
Once, the supply voltage was 3.7V instead of 3.3V. Then I replaced the diodes with voltage regulator.
So the scheme was as follows:
And usb stopped working. (Invalid USB device, Windows said)
Other functions of the scheme still work.
According to datasheet, Attiny85 can not keep the requested frequency of 16.5 MHz at 3.3 volts. And I lowered the frequency to 12.8 MHz. But it did not help. Scheme with diodes works on 12,8 mhz too.
Why this difference of 0.4 volts so important?