FT245RL-REEL Datasheet, PDF (27/37 Pages) Future Technology Devices International Ltd. – FT245R USB FIFO IC

8.2 Using the External Oscillator
Document No.: FT_000052
FT245R USB FIFO IC Datasheet Version 2.12
Clearance No.: FTDI# 39
The FT245R defaults to operating using its own internal oscillator. This requires that the device is
powered with VCC (min)=+4.0V. This supply voltage can be taken from the USB VBUS. Applications
which require using an external oscillator, VCC= +3.3V must do so in the following order:
1. When device powered for the very first time, it must have VCC > +4.0V. This supply is available
from the USB VBUS supply = +5.0V.
2. The EEPROM must then be programmed to enable external oscillator. This EEPROM modification
cannot be done using the FTDI programming utility, MPROG and FT_PROG. The EEPROM can
only be re-configured from a custom application. Please refer to the following applications note on
how to do this:
http://www.ftdichip.com/Documents/AppNotes/AN_100_Using_The_FT232_245R_With_External_
Osc(FT_000067).pdf
3. The FT245R can then be powered from VCC=+3.3V and an external oscillator. This can be done
using a link to switch the VCC supply.
The FT245R will fail to operate when the internal oscillator has been disabled, but no external oscillator
has been connected.
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