ft232
TRANSCRIPT
FT232BM Designers Guide
DG232 Version 2.0 © Future Technology Devices Intl. Ltd. 2002/2003 Page 1 of 16
FT232BM Designers GuideVersion 2.0
Introduction
Welcome to the FT232BM Designer’s Guide. The Designers Guide includes printouts of a number of FT232BM reference schematics and explanations of the key points of each schematic. These are intended to be used in conjunction with the FT232BM data sheet, the current version of which should also be downloaded from the FTDI web site.
The schematic files are downloadable separately as a ZIP archive which contains the schematics both in OrCAD SDT 16-bit DOS format and in OrCAD Capture for Windows 32-bit format.
The OrCAD SDT 16-bit DOS format schematics are readable by OrCAD SDT version 3.2 and above. These consist of files with the following extensions –• .sch = OrCAD 16-bit DOS binary schematic file• .lib = OrCAD 16-bit DOS binary component library file• .src = OrCAD DOS library source ( text ) fileThe OrCAD Capture for Windows schematics are readable by OrCAD Capture version 7.2 and above. These consist of a file with a .dsn extension.
Notes for Protel users
OrCAD 16-bit DOS schematics can be imported into Protel schematic capture for Windows. Before reading in the schematic ( .sch ) file, create a Protel library first by reading in the OrCAD library source ( .src ) file and save it in Protel binary library format. Both OrCAD and Protel use the same default extensions for schematic and library files, so if you do not wish to overwrite the original OrCAD files, save the Protel versions to a different folder.
FT232BM Designers Guide
DG232 Version 2.0 © Future Technology Devices Intl. Ltd. 2002/2003 Page 2 of 16
Figure 1.0 FT232BM – 5 volt Bus Powered Example Schematic ( 232-5VB )
DEC
OU
PLIN
G C
APS
USB
( Opt
iona
l )
FT23
2B A
PPLI
CAT
ION
SC
HEM
ATIC
INTE
RFA
CIN
G T
O 5
V L
OG
IC -
BUS
POW
ERED
( <=
100
mA
) APP
LIC
ATIO
N
5v M
CU
or L
ogic
cct
RXD
TXD
CTS
#
RTS
#
POW
ERD
N#
VCC
-5v
GN
D
RES
ET#
RST
OU
T#
SLEE
P#
RST
OU
T#VC
C
VCC
VCC
VCC
VCC
VCC
VCC
R6
1k5
U2
93C
46/5
6/66
1 2 3 4
8 7 6 5
CS
SK DIN
DO
UT
VCC NC
NC
GN
D
R1
10k
CN
1C
N-U
SB1 2 3 4
5
FB1
FER
RIT
E BE
AD
12
C5
10nF
C4
33nF
R5
27R
R4
27R
Y16M
Hz
RES
ON
ATO
R
R2
2k2
R3
470R
C6
0.1u
F
C2
0.1u
FC
10.
1uF
C3
10uF
U1
FT23
2BM
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29
9
18
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31
141516 12 1011
13
6
30
263
8 7 27
TXD
RXD
RTS
#
CTS
#
DTR
#
DSR
#
DC
D#
RST
OU
T#
XTO
UT
RES
ET#
EEC
S
EESK
EED
ATA
AGND
GND
RI#
GND
TEST
PWR
CTL
PWR
EN#
TXD
EN
TXLE
D#
SLEE
P#
RXL
ED#
VCC-IO
3V3O
UT
AVCC
VCCVCC
USB
DM
USB
DP
XTIN
C7
0.1u
F
R7
47k
FT232BM Designers Guide
DG232 Version 2.0 © Future Technology Devices Intl. Ltd. 2002/2003 Page 3 of 16
Figure 1.0 is an example of a 5 volt, USB bus powered design using the FT232BM connected to a 5v MCU or other external logic. • In this example, we assume that the total current of the design is <= 100mA ( low power ), and that the
MCU / logic can detect USB suspend mode using either the SLEEP# or PWREN# pins of the FT232BM and put itself and any circuitry it is controlling into a low power state in order to meet the total USB suspend current requirement of 500uA or less.
• RSTOUT# is used to provide a power-on reset to the external logic in this example. If the MCU has it’s own power-on reset logic then there is usually no need to use RSTOUT# to reset the device and this connection and the 47k pull-down can be omitted.
• PWRCTL is tied to GND to tell the device to indicate a bus powered device in it’s USB descriptor.• RTS / CTS handshaking is used in this example. If the MCU has no dedicated handshaking signals then
general purpose IO pins can usually be used to implement the handshaking. If the MCU is guaranteed to accept data sent from the FT232BM at the programmed baud rate, then a single wire handshake will do ( tie CTS# of the FT232BM to GND ).
General Design Notes:
• SLEEP# goes inactive ( high ) at power-on and goes low during USB suspend. PWREN# is high on power-on and only goes low ( active ) after the device has been configured ( successfully enumerated ) by USB. During USB suspend PWREN# will go high – the opposite polarity to SLEEP#. For a low power bus powered USB device , either SLEEP# or PWREN# can be used for power control, however for a high power bus powered USB device ( 100mA .. 500mA ) you must use PWREN# for power control as no USB device is allowed to draw more than 100mA from the bus until USB configuration is complete.
• RSTOUT# has no pull-down capability – it drives to 3.3v when not in reset, and goes tri-state during power-on reset. If used to reset an external device, a pull-down resistor must be added to make it low during reset.
• When RTS/CTS hardware handshaking is enabled CTS# can be used to stop the FT232BM transmitting data to the MCU / external logic. When CTS# is active ( low ) the FT232BM will transmit any data in it’s internal buffers. On taking CTS# high, the FT232BM will stop transmitting data. Due to the asynchronous nature of the interface, there is a latency of 0 to 3 characters between taking CTS# high and data transmission stopping. The FT232BM drives RTS# high when the available buffer space inside the device drops below 32 bytes. This allows the MCU / logic to continue to send up to 30 characters to the FT232BM after RTS# goes high without causing buffer over-run.
• A suitable 3-pin ceramic resonator could be a Murata CSTCR6M00G15 or equivalent. See http://www.murata.com/catalog/p63e.pdf for details If you prefer to use a 2 pin resonator or a crystal refer to Figures 4 and 5 of the FT232BM data sheet for details.
• A suitable ferrite bead could be a Steward MI0805K400R-00 or equivalent. This is also available from DigiKey as Part # 240-1035-1. For specifications consult the Steward web site - http://www.steward.com
FT232BM Designers Guide
DG232 Version 2.0 © Future Technology Devices Intl. Ltd. 2002/2003 Page 4 of 16
Figure 2.0 FT232BM – 5 volt Self Powered Example Schematic ( 232-5VS )
DEC
OU
PLIN
G C
APS
USB
( Opt
iona
l )
FT23
2B A
PPLI
CAT
ION
SC
HEM
ATIC
5v M
CU
or L
ogic
cct
INTE
RFA
CIN
G T
O 5
V L
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IC -
SELF
PO
WER
ED A
PPLI
CAT
ION
UPD
ATED
21s
t Jan
uary
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3
RXD
TXD
CTS
#
RTS
#
POW
ERD
N#
VCC
-5v
GN
D
EXTE
RN
AL 5
V PO
WER
SLEE
P#
VCC
VCC
VCC
VCC
VCC
VCC
VCC
R7
1k5
U2
93C
46/5
6/66
1 2 3 4
8 7 6 5
CS
SK DIN
DO
UT
VCC NC
NC
GN
D
R1
10k
CN
1C
N-U
SB1 2 3 4
5
C4
33nF
R5
27R
R4
27R
Y16M
Hz
RES
ON
ATO
R
R2
2k2
R6
10k
R3
470R
C5
0.1u
F
C2
0.1u
FC
10.
1uF
C3
10uF
U1
FT23
2BM
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5 28 4 32 1 2
29
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17
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141516 12 1011
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TXD
RXD
RTS
#
CTS
#
DTR
#
DSR
#
DC
D#
RST
OU
T#
XTO
UT
RES
ET#
EEC
S
EESK
EED
ATA
AGND
GND
RI#
GND
TEST
PWR
CTL
PWR
EN#
TXD
EN
TXLE
D#
SLEE
P#
RXL
ED#
VCC-IO
3V3O
UT
AVCC
VCCVCC
USB
DM
USB
DP
XTIN
C6
0.1u
F
R8
15k
VCC
GN
D
FT232BM Designers Guide
DG232 Version 2.0 © Future Technology Devices Intl. Ltd. 2002/2003 Page 5 of 16
Figure 2.0 is an example of a 5 volt, USB self powered design using the FT232BM connected to a 5v MCU or other external logic. A USB self power design has it’s own PSU and does not draw it’s power from the USB bus. In such a case, no special care need be taken to meet the USB suspend current ( 0.5mA ) as the device does not get its power from the USB port.• In this case it is still useful to connect SLEEP# ( or PWREN# ) to the CPU as this will let the CPU know
that the PC is in suspend mode and thus unable to communicate with the device. If the device requires to “wake up” the PC then the MCU should connect one of it’s IO Ports to the Ring Indicator pin ( RI# ). The default state of RI# should be high - strobing this low for a few milliseconds then taking it high again will cause a USB resume sequence thus requesting the PC to wake up. To use this feature, Remote Wake-Up must be enabled in the 93C46 EEPROM.
• PWRCTL is tied to VCC to tell the device to indicate a self powered device in it’s USB descriptor.• RTS / CTS handshaking is used in this example. If the MCU has no dedicated handshaking signals then
general purpose IO pins can usually be used to implement the handshaking. If the MCU is guaranteed to accept data sent from the FT232BM at the programmed baud rate, then a single wire handshake will do ( tie CTS# of the FT232BM to GND ).
• Self powered designs should NOT force current back into the Host PC ( or HUB ) via the USB Port when the said Host / Hub is powered down and the self powered device is still powered-up from it’s own PSU. This rule includes injecting current into the powered down Host / Hub via the 1k5 pull-up on USB D+. Failure to do this can result in unreliable operation in the field. This is an integral part of the USB specification and applies to all USB Self Powered devices ( not just FT232BM peripherals ). In this design, the presence of power on the host/hub USB port is used to control the RESET# pin of the FT232BM. When the Host / Hub is powered up RSTOUT# pulls the top end of the 1k5 resistor on USB D+ to 3.3v nominal thus identifying the device as a full speed device to USB. When the Host / HUB powers down, the FT232BM is reset and RSTOUT# will go low thus preventing current being injected into the Host / Hub USB D+ line via the 1k5 resistor.
General Design Notes – See Previous Example
FT232BM Designers Guide
DG232 Version 2.0 © Future Technology Devices Intl. Ltd. 2002/2003 Page 6 of 16
Figure 3.0 FT232BM – 5 volt Bus Powered Example Schematic with Power Switching ( 232-5VSW )
DEC
OU
PLIN
G C
APS
USB
( Opt
iona
l )
FT23
2B A
PPLI
CAT
ION
SC
HEM
ATIC
5v M
CU
or L
ogic
cct
WIT
H P
OW
ER S
WIT
CH
ING
Soft
Star
tC
ircui
t
PO
WER
ED A
PPLI
CAT
ION
RXD
TXD
CTS
#
RTS
#
VCC
-5v
GN
DVC
C
VCC
VCC
VCC
VCC
VCC
R6
1k5
U2
93C
46/5
6/66
1 2 3 4
8 7 6 5
CS
SK DIN
DO
UT
VCC
NC
NC
GN
D
R1
10k
CN
1C
N-U
SB1 2 3 4
5
FB1
FER
RIT
E BE
AD
12
C5
10nF
C4
33nF
R5
27R
R4
27R
Y16M
Hz
RES
ON
ATO
R
R2
2k2
R3
470R
C6
0.1u
F
C2
0.1u
FC
10.
1uF
C3
10uF
U1
FT23
2BM
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5 28 4 32 1 2
29
9
18
17
31
141516 12 1011
13
6
30
263
8 7 27
TXD
RXD
RTS
#
CTS
#
DTR
#
DSR
#
DC
D#
RST
OU
T#
XTO
UT
RES
ET#
EEC
S
EESK
EED
ATA
AGND
GND
RI#
GND
TEST
PWR
CTL
PWR
EN#
TXD
EN
TXLE
D#
SLEE
P#
RXL
ED#
VCC-IO
3V3O
UT
AVCC
VCCVCC
USB
DM
USB
DP
XTIN
R7
1k
C8
0.1u
F
C7
0.1u
F
Q1
IRLM
L640
2
FT232BM Designers Guide
DG232 Version 2.0 © Future Technology Devices Intl. Ltd. 2002/2003 Page 7 of 16
Figure 3.0 is an example of a 5 volt, USB bus powered design using the FT232BM connected to a 5v MCU or other external logic. In this design, the FT232BM controls the power to the auxiliary circuitry using PWEREN# to shut off power to this circuitry when –
1. The FT232BM is in reset, OR2. The FT232BM has not yet been configured ( successfully recognised and enumerated over USB ), OR3. USB is in suspend / sleep mode.
• A P-Channel Logic Level MOSFET is used as a power switch to control the power to the auxiliary devices – in this example we use a International Rectifier part number IRLML6402. R7 and C8 form a “soft start” circuit which limits the current surge when the MOSFET turns on. Without this, there is a danger that the transient power surge of the MOSFET turning on will reset the FT232BM or the USB Host / Hub controller. The values used allow the attached circuitry to power up with a slew rate of ~ 12.5v per millisecond, in other words the output voltage will transitioning from GND to 5v in around 400uS.
• When using this circuit, enable the “Pull-Down on Suspend” option in the EEPROM. This will ensure minimum leakage current during sleep ( suspend ) mode by gently pulling down the UART interface pins of the FT232BM pins to GND during USB suspend.
• The auxiliary circuitry attached to the FT232BM device must have it’s own power-on-reset circuitry and should NOT use RESETO# to generate a reset for this circuitry. RESETO# does not generate a reset during USB sleep ( suspend ) when the auxiliary logic is powered-off, thus cannot be used as a reset in this case.
• A “USB High-Power Bus Powered Device” ( one that consumes more than 100mA and up to 500mA ) of current from the USB bus during normal operation must use this power control feature to remain compliant as the USB specification does not allow a USB peripheral to draw more than 100mA of current from the USB Bus until the device has been successfully enumerated. A “USB High-Power Bus Powered Device” cannot be plugged into a USB Bus-Powered Hub as these can only supply 100mA per USB port.
• The Power ( current ) consumption of the device is set in a field in the 93C46 EEPROM attached to the FT232BM. A “USB High-Power Bus Powered Device” must use the 93C46 to inform the system of it’s power requirements.
• PWRCTL is tied to GND to tell the device to indicate a bus powered device in it’s USB descriptor.• RTS / CTS handshaking is used in this example. If the MCU has no dedicated handshaking signals then
general purpose IO pins can usually be used to implement the handshaking. If the MCU is guaranteed to accept data sent from the FT232BM at the programmed baud rate, then a single wire handshake will do ( tie CTS# of the FT232BM to GND ).
General Design Notes – See Previous Examples
FT232BM Designers Guide
DG232 Version 2.0 © Future Technology Devices Intl. Ltd. 2002/2003 Page 8 of 16
Figure 4.0 FT232BM – 3.3 volt Bus Powered Example Schematic ( 232-3VB )
DEC
OU
PLIN
G C
APS
USB
( Opt
iona
l )
FT23
2B A
PPLI
CAT
ION
SC
HEM
ATIC
INTE
RFA
CIN
G T
O 3
.3 V
LO
GIC
- BU
S PO
WER
ED (
<= 1
00m
A ) A
PPLI
CAT
ION
3.3v
MC
U o
r Log
ic c
ct
RXD
TXD
CTS
#
RTS
#
POW
ERD
N#
GN
D
VCC
-3.3
v
RES
ET#
VCC
-3.3
V
RST
OU
T#
SLEE
P#
RST
OU
T#VC
C
VCC
VCC
VCC
VCC
VCC
IO
G
U3
LDO
REG
ULA
TOR
3.3
v
R6
1k5
U2
93C
46/5
6/66
1 2 3 4
8 7 6 5
CS
SK DIN
DO
UT
VCC NC
NC
GN
D
R1
10k
CN
1C
N-U
SB1 2 3 4
5
FB1
FER
RIT
E BE
AD
12
C5
10nF
C4
33nF
R5
27R
R4
27R
Y16M
Hz
RES
ON
ATO
R
R2
2k2
R3
470R
C6
0.1u
F
R7
47k
C2
0.1u
FC
10.
1uF
C3
10uF
U1
FT23
2BM
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5 28 4 32 1 2
29
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18
17
31
141516 12 1011
13
6
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263
8 7 27
TXD
RXD
RTS
#
CTS
#
DTR
#
DSR
#
DC
D#
RST
OU
T#
XTO
UT
RES
ET#
EEC
S
EESK
EED
ATA
AGND
GND
RI#
GND
TEST
PWR
CTL
PWR
EN#
TXD
EN
TXLE
D#
SLEE
P#
RXL
ED#
VCC-IO
3V3O
UT
AVCC
VCCVCC
USB
DM
USB
DP
XTIN
C7
0.1u
F
FT232BM Designers Guide
DG232 Version 2.0 © Future Technology Devices Intl. Ltd. 2002/2003 Page 9 of 16
Figure 4.0 is an example of a 3.3 volt, USB bus powered design using the FT232BM connected to a 3.3v MCU or other external logic. • The main difference between this circuit and the 5 volt circuit of Figure 1.0 is that a 3.3 volt LDO regulator
i.c. is used to provide a 3.3v supply to the auxiliary circuiry. • VCC-IO is driven from the 3.3v LDO regulator i.c. in order to drive the UART interface from the FT232BM to
the MCU / external logic at 3.3v level instead of 5v level.• As the USB supply rail can drop to 4.4 volts or less under load, an LDO ( Low Dropout ) voltage regulator
must be used in this instance.• The 3.3v LDO voltage regulator must also have a low quiescent ( no load ) current in order to ensure that
the USB suspend current requirement ( <= 500uA ) is met during USB suspend.• In this example, we assume that the total current of the design is <= 100mA ( low power ), and that the
MCU / logic can detect USB suspend mode using either the SLEEP# or PWREN# pins of the FT232BM and put itself and any circuitry it is controlling into a low power state in order to meet the total USB suspend current requirement of 500uA or less.
• RSTOUT# is used to provide a power-on reset to the external logic in this example. If the MCU has it’s own power-on reset logic then there is usually no need to use RSTOUT# to reset the device and this connection and the 47k pull-down can be omitted. Note : If RSTOUT# is used to reset an external device AND to pull-up the USB D+ line, it’s Vout high can be as low as 2.2v so it must be used to drive a TTL level reset input on the external device.
• PWRCTL is tied to GND to tell the device to indicate a bus powered device in it’s USB descriptor.• RTS / CTS handshaking is used in this example. If the MCU has no dedicated handshaking signals then
general purpose IO pins can usually be used to implement the handshaking. If the MCU is guaranteed to accept data sent from the FT232BM at the programmed baud rate, then a single wire handshake will do ( tie CTS# of the FT232BM to GND ).
General Design Notes – See Previous Examples
FT232BM Designers Guide
DG232 Version 2.0 © Future Technology Devices Intl. Ltd. 2002/2003 Page 10 of 16
Figure 5.0 FT232BM – 3.3 volt Self Powered Example Schematic ( 232-3VS )
DEC
OU
PLIN
G C
APS
USB
( Opt
iona
l )
FT23
2B A
PPLI
CAT
ION
SC
HEM
ATIC
3.3v
MC
U o
r Log
ic c
ct
INTE
RFA
CIN
G T
O 3
.3V
LOG
IC -
SELF
PO
WER
ED A
PPLI
CAT
ION
UPD
ATED
21s
t Jan
uary
200
3
RXD
TXD
CTS
#
RTS
#
VCC
-3v
GN
D
EXTE
RN
AL P
OW
ER
POW
EREN
#
VCC
VCC
VCC
VCC
VCC
VCC
3VVCC
3V
R6
1k5
U2
93C
46/5
6/66
1 2 3 4
8 7 6 5
CS
SK DIN
DO
UT
VCC NC
NC
GN
D
R1
10k
CN
1C
N-U
SB1 2 3 4
5
C4
33nF
R5
27R
R4
27R
Y16M
Hz
RES
ON
ATO
R
R2
2k2
R8
10k
R7
15k
R3
470R
C5
0.1u
F
C2
0.1u
FC
10.
1uF
C3
10uF
U1
FT23
2BM
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5 28 4 32 1 2
29
9
18
17
31
141516 12 1011
13
6
30
263
8 7 27
TXD
RXD
RTS
#
CTS
#
DTR
#
DSR
#
DC
D#
RST
OU
T#
XTO
UT
RES
ET#
EEC
S
EESK
EED
ATA
AGND
GND
RI#
GND
TEST
PWR
CTL
PWR
EN#
TXD
EN
TXLE
D#
SLEE
P#
RXL
ED#
VCC-IO
3V3O
UT
AVCC
VCCVCC
USB
DM
USB
DP
XTIN
C6
0.1u
F
GN
D
VCC
3.3
v
VCC
5.0
v
FT232BM Designers Guide
DG232 Version 2.0 © Future Technology Devices Intl. Ltd. 2002/2003 Page 11 of 16
Figure 5.0 is an example of a 3.3 volt, USB self powered design using the FT232BM connected to a 3.3v MCU or other external logic. A USB self power design has it’s own PSU and does not draw it’s power from the USB bus. In such a case, no special care need be taken to meet the USB suspend current ( 0.5mA ) as the device does not get its power from the USB port. The differences between this circuit and that of Figure 2.0 are minimal. See the notes in Figure 2 for the main details.
• In this case the internal PSU needs to supply 3.3 volts to the auxiliary circuitry and 5 volts to the FT232BM i.c.
• The VCCIO power line to the FT232BM is driven from the 3.3v supply in order to drive the auxiliary logic at the correct voltage level.
Important Note : In this design, the PWRCTL Pin ( Pin 14 ) of the FT232BM is tied high to indicate a self powered design. It is important to tie this to VCCIO ( 3.3v ) and NOT to VCC ( 5.0v ) otherwise the input protection diodes on this pin will conduct and try to pull VCCIO towards 5.0v As well as being undesirable, this may cause excessive current to be drawn by the FT232BM and the 3.3v logic attached to this device.
FT232BM Designers Guide
DG232 Version 2.0 © Future Technology Devices Intl. Ltd. 2002/2003 Page 12 of 16
Figure 6.0 FT232BM – 3.3 volt Switched Power Bus Powered Schematic ( 232-3VSW)
DEC
OU
PLIN
G C
APS
USB
( Opt
iona
l )
FT23
2B A
PPLI
CAT
ION
SC
HEM
ATIC
3v M
CU
or L
ogic
cct
WIT
H P
OW
ER S
WIT
CH
ING
INTE
RFA
CIN
G T
O 3
.3 V
LO
GIC
- BU
S PO
WER
ED (
<= 2
50m
A ) A
PPLI
CAT
IONSo
ft St
art
Circ
uit
RXD
TXD
CTS
#
RTS
#
VCC
-3v
GN
DVC
C
VCC
VCC
VCC
VCC
VCC
R6
1k5
U2
93C
46/5
6/66
1 2 3 4
8 7 6 5
CS
SK DIN
DO
UT
VCC
NC
NC
GN
D
R1
10k
CN
1C
N-U
SB1 2 3 4
5
FB1
FER
RIT
E BE
AD
12
C4
10nF
C3
33nF
R5
27R
R4
27R
Y16M
Hz
RES
ON
ATO
R
R2
2k2
C10
0.1u
F
R7
1k
Q1
IRLM
L640
2
C9
0.1u
F
GVi
Vo
REG
1TC
55R
P330
2
1
2
3
R3
470R
C5
0.1u
F
C2
0.1u
FC
10.
1uF
C7
4.7u
F
C8
4.7u
F
U1
FT23
2BM
25 24 23 22 21 20 19
5 28 4 32 1 2
29
9
18
17
31
141516 12 1011
13
6
30
263
8 7 27
TXD
RXD
RTS
#
CTS
#
DTR
#
DSR
#
DC
D#
RST
OU
T#
XTO
UT
RES
ET#
EEC
S
EESK
EED
ATA
AGND
GND
RI#
GND
TEST
PWR
CTL
PWR
EN#
TXD
EN
TXLE
D#
SLEE
P#
RXL
ED#
VCC-IO
3V3O
UT
AVCC
VCCVCC
USB
DM
USB
DP
XTIN
C6
0.1u
F
FT232BM Designers Guide
DG232 Version 2.0 © Future Technology Devices Intl. Ltd. 2002/2003 Page 13 of 16
Figure 6.0 is an example of a 3.3 volt, USB bus powered design with power switching using the FT232BM connected to a 3.3v MCU or other external logic. The circuit is essentially a combination of the schematics of Figure 3 and Figure 4.• A 3.3 volt LDO regulator i.c. is used to provide a 3.3v VCCIO rail and switched 3.3v supply to the auxiliary
circuiry via a IRLML6402 P-Channel MOSFET .• In this example, we use a Telcom / MicroChip TC55RP3302 as the 3.3v LDO regulator. This has a maximum
rated output current of 250mA. If a higher current is required, use an LD1117 / LM1117 series LDO regulator instead as these are rated to 800mA. The two are not pin compatible.
• R7 and C10 form a soft start circuit which helps prevent excesssive power switching transients when the MOSFET turns on. We would advise you to include these components as without them the current surge when the IRLML6402 MOSFET initially turns on can be capable of resetting the FT232BM or tripping the power sense circuitry in a USB hub.
General Design Notes – See Previous Examples
FT232BM Designers Guide
DG232 Version 2.0 © Future Technology Devices Intl. Ltd. 2002/2003 Page 14 of 16
Figure 7.0 FT232BM –5v BUS Powered USB => RS232 Converter Example Schematic ( USB-232B )
DEC
OU
PLIN
G C
APS
MAX
213C
WI
ADM
213E
SP21
3EC
A
TXR
X
USB
( Opt
iona
l )
USB
<=>
RS2
32 S
ERIA
L C
ON
VER
TER
( 30
0 to
115
k/46
0k b
aud
)
SP21
3EH
CA
FT23
2B A
PPLI
CAT
ION
SC
HEM
ATIC
RI
DTR
CTS
TXD
ATA
SHIE
LDR
TSTX
DR
XDAT
AD
SRR
XDD
CD
RTS
#
CTS
#
DTR
#SH
IELD
DSR
#
DC
D#
RI#
TXD
TXD
ATA
DTR
#D
TRR
TS#
RTS
CTS
CTS
#D
SRD
SR#
DC
DD
CD
#R
XDAT
AR
XDSL
EEP#
RI
RI#
SLEE
P#VC
C
VCC
GN
D
VCC
VCC
VCC
VCC
VCC
VCC
VCC
VCC
VCC
VCC
C1
0.1u
FC
20.
1uF
C3
0.1u
FC
410
uF
D1
LED
R1
220R
C5
0.1u
F
C6
0.1u
F
U1
MAX
213C
AI
7 6 20 21 9 4 27 23 18
2 3 1 28 8 5 26 22 19
25 24 1317
12 1415 16
1011
T1IN
T2IN
T3IN
T4IN
R1I
NR
2IN
R3I
NR
4IN
R5I
N
T1O
UT
T2O
UT
T3O
UT
T4O
UT
R1O
UT
R2O
UT
R3O
UT
R4O
UT
R5O
UT
SHD
N#
EN V+V-
C1+
C1-
C2+ C2-
GN
DVC
C
C7
0.1u
F
C8
0.1u
F
SKT1
DB9
M5 9 4 8 3 7 2 6 1
10
D2
LED
R2
220R
CN
1C
N-U
SB1 2 3 4
5
R3
10k
C9
33nF
C10
10nF
R4
2k2
FB1
FER
RIT
E BE
AD
12
C11
0.1u
F
R5
470R
U2
FT23
2BM
25 24 23 22 21 20 19
5 28 4 32 1 2
29
9
18
17
31
141516 12 1011
13
6
30
263
8 7 27
TXD
RXD
RTS
#
CTS
#
DTR
#
DSR
#
DC
D#
RST
OU
T#
XTO
UT
RES
ET#
EEC
S
EESK
EED
ATA
AGND
GND
RI#
GND
TEST
PWR
CTL
PWR
EN#
TXD
EN
TXLE
D#
SLEE
P#
RXL
ED#
VCC-IO
3V3O
UT
AVCC
VCCVCC
USB
DM
USB
DP
XTIN
Y16M
Hz
RES
ON
ATO
R
R6
27R
R7
27R
R8
1k5
U3
93C
46/5
6/66
1 2 3 4
8 7 6 5
CS
SK DIN
DO
UT
VCC
NC
NC
GN
D
FT232BM Designers Guide
DG232 Version 2.0 © Future Technology Devices Intl. Ltd. 2002/2003 Page 15 of 16
Figure 7.0 is an example of a 5 volt, USB bus powered design using the FT232BM connected to a TTL ó RS232 level converter i.c . • For RS232 applications, the baud rate of the finished product is limited by the ac. driving characteristics
of the level converter i.c. rather than that of the FT232BM. • This example uses the popular “213” series of TTL to RS232 level converters. These devices have 4
transmitters and 5 receivers in a 28 LD SSOP package and feature an in-built voltage converter to convert the 5v ( nominal ) VCC to the +/- 9volts required by RS232. An important feature of these devices is the SHDN# pin which can power down the device to a low quiescent current during USB suspend mode
• The device used in this schematic is a Sipex SP213EHCA which is capable of RS232 communication at up to 500k baud. If a lower baud rate is acceptable, then several pin compatible alternatives are available such as Sipex SP213ECA , Maxim MAX213CAI and Analog Devices ADM213E which are good for communication at up to 115,200 baud. If a higher baud rate is desired, use a Maxim MAX3245CAI part which is capable of RS232 communication at rates of up to 1M baud.
• Note : the MAX3245 is not pin compatible with the 213 series devices, also it’s SHDN pin is active high so connect this to PWREN# instead of SLEEP#.
FT232BM Designers Guide
DG232 Version 2.0 © Future Technology Devices Intl. Ltd. 2002/2003 Page 16 of 16
Document Revision History
DG232B Version 1.0 – Initial document created 05 August 2002DG232B Version 1.1 - Created 06 August 2002 • Added USB-232B applicationDG232B Version 2.0 - Created 19th May 2003 • Corrected Pull Up Control Circuit for Self Powered Designs • Corrected connection of PWRCTL in 3.3v Self Powered Designs • Updated Schematic Drawings • Added 3.3v Switched Bus Powered reference schematic
Disclaimer
© Future Technology Devices International Limited , 2002 / 2003
Neither the whole nor any part of the information contained in, or the product described in this manual, maybe adapted or reproduced in any material or electronic form without the prior written consent of the copyrightholder.This product and its documentation are supplied on an as-is basis and no warranty as to their suitability forany particular purpose is either made or implied.Future Technology Devices International Ltd. will not accept any claim for damages howsoever arising as aresult of use or failure of this product. Your statutory rights are not affected.This product or any variant of it is not intended for use in any medical appliance, device or system in whichthe failure of the product might reasonably be expected to result in personal injury.The information in this document may be subject to change without notice.
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