FT231XS-U FTDI, FT231XS-U Datasheet - Page 27

• Manufacturer Part Number: FT231XS-U
• Description: USB Interface IC USB to Full Serial UART IC SSOP-20
• Manufacturer: FTDI

Specifications of FT231XS-U

• Rohs: yes
• Tradename: X-Chip

7.3 USB to RS422 Converter
Figure 7.3 USB to RS422 Converter Configuration
An example of using the FT231X as a USB to RS422 converter is shown in Figure 7.3. In this application,
two 3V3-TTL to RS422 Level Converter Ics are used on the serial UART interface of the FT231X to convert
the TTL levels of the FT231X to RS422 levels. There are many suitable level converter devices available.
This example uses Zywyn ZT3491 devices which have enables on both the transmitter and receiver.
Since the ZT3491 transmitter enable is active high, it is connected to a CBUS pin in SLEEP#
configuration. The ZT3491 receiver enable is active low and is therefore connected to a CBUS pin
PWREN# configuration. This ensures that when both the ZT3491 transmitters and receivers are enabled
then the device is active, and when the device is in USB suspend mode, the ZT3491 transmitters and
receivers are disabled. If a similar application is used, but the design is USB BUS powered, it may be
necessary to use a P-Channel logic level MOSFET (controlled by PWREN#) in the VCC line of the ZT3491
devices to ensure that the USB standby current of 2.5mA is met.
The ZT3491 is specified to transmit and receive data at a rate of up to 16 Mbaud. In this example the
maximum data rate is limited to 3 Mbaud by the FT231X.
SHIELD
5
1
2
3
4
Copyright © 2013 Future Technology Devices International Limited
100nF
GND
10nF
Ferrite
Bead
47pF
VCC
+
GND
4.7uF
GND
VCC
47pF
GND
27R
27R
100nF
USBDM
USBDP
VCC
RESET#
VCCIO
3V3OUT
FT231X USB TO FULL HANDSHAKE UART IC
FT231X
PWREN#
SLEEP#
RTS#
CTS#
RXD
TXD
Document No.: FT_000565 Clearance No.:
10K
Vcc
4
5
3
2
5
4
3
2
RS 422 LEVEL
6
RS 422 LEVEL
6
CONVERTER
CONVERTER
ZT3491
ZT3491
RXDM
TXDM
RXDP
RTSM
CTSM
TXDP
RTSP
CTSP
Vcc
Vcc
7
7
GND
SHIELD
10
11
12
10
11
12
9
9
120R
120R
DB9M
Datasheet
Version 1.2
FTDI# 261
RXDP
TXDM
TXDP
RXDM
RTSM
CTSM
RTSP
CTSP
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