FT232BL 参数 Datasheet PDF下载

FT232BL USB UART ( USB - Serial) I.C.

7.0

7.1

Device Configuration Examples

Oscillator Configurations

Figure 4

3-Pin Ceramic Resonator

Configuration

FT223BM

Figure 5

Crystal or 2-Pin Ceramic Resonator

Configuration

FT232BM

27pF

FT232BL

27

3-Pin Resonator

6MHz

XTIN

FT232BL

27

XTIN

1M

2 - Pin Resonator

or Crystal

6MHz

27pF

28

XTOUT

28

XTOUT

Figure 4 illustrates how to use the FT232BL with a 3-Pin Ceramic Resonator. A suitable part would be a ceramic

resonator from Murata’s CERALOCK range. (Murata Part Number CSTCR6M00G15), 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.

Other ceramic resonators with a lesser degree of accuracy (typically +/- 0.5%) are technically out-with the USB

specification, but it has been calculated that using such a device will work satisfactorily in practice with a FT232BL

design.

Figure 5 illustrates how to use the FT232BL with a 6MHz Crystal or 2-Pin Ceramic Resonator. In this case, these

devices do not have in-built loading capacitors so these have to 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 manufacturers recommendations wherever possible. If using a crystal,

use a parallel cut type. If using a resonator, see the previous note on frequency accuracy.

DS232BL Version 1.8

© Future Technology Devices Intl. Ltd. 2005

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