FT230X USB TO BASIC UART IC
Document No.: FT_000566 Clearance No.: FTDI# 260
Version 1.2
7.3 USB to RS422 Converter
Vcc
VCC
1
2
3
4
47pF
5
SHIELD
RESET#
10nF
VCCIO
GND
3V3OUT
AG
ND
Ferrite
Bead
VCC
27R
USBDM
27R
USBDP
47pF
RXD
TXD
RTS#
CTS#
4
RS 422 LEVEL
CONVERTER
10
9
5
3
FT230X
2
11
12
ZT3491
SLEEP#
PWREN#
6
Vcc
7
GND
GN
D
VCC
100nF
+
4.7uF
GND
RS 422 LEVEL
CONVERTER
4
10
5
9
3
11
2
100nF
GND
VCCIO
12
ZT3491
7
Vcc
6
10K
RXD
TXD
RTS
CTS
GND
TXDM
TXDP
RXDP
RXDM
RTSM
RTSP
CTSP
CTSM
SHIELD
Figure 7.3 USB to RS422 Converter Configuration
An example of using the FT230X as a USB to RS422 converter is shown in Figure 7.3. In this application,
two TTL to RS422 Level Converter ICs are used on the serial UART interface of the FT230X to convert the
TTL levels of the FT230X 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 FT230X.
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27
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