FT245RQ R FTDI, Future Technology Devices International Ltd, FT245RQ R Datasheet - Page 24

• Manufacturer Part Number: FT245RQ R
• Description: IC USB TO PARALLEL FIFO 32-QFN
• Manufacturer: FTDI, Future Technology Devices International Ltd

Specifications of FT245RQ R

• Applications: USB
• Interface: USB
• Voltage - Supply: 1.8 V ~ 5.25 V
• Package / Case: 32-QFN
• Mounting Type: Surface Mount
• For Use With: 768-1020 - MODULE USB-PAR FIFO TTL 24-DIP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 768-1012-2; FT245RQ R

7.3 USB Bus Powered with Power Switching Configuration
Figure 7.3 Bus Powered with Power Switching Configuration
A requirement of USB bus powered applications, is when in USB suspend mode the application draws a
total current of less than 2.5mA. This requirement includes external logic. Some external logic has the
ability to power itself down into a low current state by monitoring the PWREN# signal. For external logic
that cannot power itself down in this way, the FT245R provides a simple but effective method of turning
off power during the USB suspend mode.
Figure 7.3 shows an example of using a discrete P-Channel MOSFET to control the power to external
logic. A suitable device to do this is an International Rectifier (www.irf.com) IRLML6402, or equivalent. It
is recommended that a “soft start” circuit consisting of a 1kΩ series resistor and a 0.1μF capacitor is used
to limit the current surge when the MOSFET turns on. Without the soft start circuit it is possible that the
transient power surge, caused when the MOSFET switches on, will reset the FT245R or the USB host/hub
controller. The soft start circuit example shown in Figure 7.3 powers up with a slew rate of
approximaely12.5V/ms. Thus supply voltage to external logic transitions from GND to +5V in
approximately 400 microseconds.
As an alternative to the MOSFET, a dedicated power switch IC with inbuilt “soft-start” can be used. A
suitable power switch IC for such an application is the Micrel (www.micrel.com) MIC2025-2BM or
equivalent.
With power switching controlled designs the following should be noted:
i)
ii) Set the Pull-down on Suspend option in the internal FT245R EEPROM.
iii) The PWREN# pin should be used to switch the power to the external circuitry.
iv) For USB high-power bus powered applications (one that consumes greater than 100mA, and up
The external logic to which the power is being switched should have its own reset circuitry to
automatically reset the logic when power is re-applied when moving out of suspend mode.
to 500mA of current from the USB bus), the power consumption of the application must be set in
the Max Power field in the internal FT245R EEPROM. A high-power bus powered application uses
the descriptor in the internal FT245R EEPROM to inform the system of its power requirements.
SHIELD
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Copyright © 2010 Future Technology Devices International Limited
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2
3
4
100nF
P-Channel Power
GND
10nF
+
MOSFET
Ferrite
Bead
4.7uF
GND
+
5V VCC
5V VCC
s
g
100nF
d
1k
0.1uF
GND
Soft Start
Circuit
FT245R USB FIFO IC Datasheet Version 2.10
VCC
USBDM
USBDP
3V3OUT
VCCIO
OSCI
NC
RESET#
NC
OSCO
A
G
N
D
0.1uF
G
N
D
FT245R
G
N
D
GND
G
N
D
Switched 5V Power
to External Logic
T
E
S
T
Document No.: FT_000052
PWREN#
RXF#
TXE#
Clearance No.: FTDI# 39
WR#
RD#
D0
D1
D2
D3
D4
D5
D6
D7
5V VCC
10K
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