FT232BQ-REEL Datasheet, PDF (22/34 Pages) Future Technology Devices International Ltd. – USB UART IC

Document No.: FT_000329
FT232BL/BQ USB UART IC Datasheet Version 2.2
Clearance No.: FTDI# 171
7 Device Configuration Examples
The following sections illustrate device configurations for the FT245BM.
7.1 Oscillator Configurations
Figure 7.1 3 Pin Ceramic Resonator Configuration
Figure 7.2 Crystal or 2 Pin
Ceramic Resonator Configuration
Figure 7.1 illustrates how to use the FT232B with a 3-Pin Ceramic Resonator. A suitable part would be a
ceramic resonator from Murata’s CERALOCK range or equivalent. 3-Pin ceramic resonators have the load
capacitors built into the resonator so no external loading capacitors are required. This makes for an
economical configuration. The accuracy of this Murata ceramic resonator is +/- 0.1% and it is specifically
designed for USB full speed applications. A 1 MegaOhm loading resistor across XTIN and XTOUT is
recommended in order to guarantee this level of accuracy.
Figure 7.2 illustrates how to use the FT232B with a 6MHz Crystal or 2-Pin Ceramic Resonator. These
devices do not have in-built loading capacitors. They must be added between XTIN, XTOUT and GND as
shown. A value of 27pF is shown as the capacitor in the example – this will be good for many crystals and
some resonators but do select the value based on the manufacturer’s recommendations wherever
possible. If using a crystal, use a parallel cut type. If using a resonator, see the previous note on
frequency accuracy.
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