FT245RL FTDI, FT245RL Datasheet - Page 21

IC, USB FIFO INTERFACE, SSOP-28

FT245RL

Manufacturer Part Number
FT245RL
Description
IC, USB FIFO INTERFACE, SSOP-28
Manufacturer
FTDI
Datasheet

Specifications of FT245RL

Data Rate
1Mbps
Supply Voltage Range
1.8V To 5.25V, 3.3V To 5.25V
Operating Temperature Range
-40°C To +85°C
Digital Ic Case Style
SSOP
No. Of Pins
28
Termination Type
SMD
Ic Generic Number
245
Filter Terminals
SMD
Rohs Compliant
Yes
Lead Free Status / RoHS Status
Lead free / RoHS Compliant

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Figure 15 - Bus Powered with Power Switching Configuration
USB Bus powered circuits need to be able to power down in USB suspend mode in order to meet the <= 500μA
total USB suspend current requirement (including external logic). Some external logic can 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 way of turning off power to external circuitry during USB suspend.
Figure 15 shows how to use a discrete P-Channel Logic Level MOSFET to control the power to external logic circuits.
A suitable device would be 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 are used to limit the current surge when
the MOSFET turns on. Without the soft start circuit there is a danger that the transient power surge of the MOSFET
turning on will reset the FT245R, or the USB host / hub controller. The values used here allow attached circuitry to
power up with a slew rate of ~12.5V per millisecond, in other words the output voltage will transition from GND to 5V in
approximately 400 microseconds.
Alternatively, a dedicated power switch I.C. with inbuilt “soft-start” can be used instead of a MOSFET. A suitable power
switch I.C. for such an application would be a Micrel (www.micrel.com) MIC2025-2BM or equivalent.
Please note the following points in connection with power controlled designs –
i)
ii) Set the Pull-down on Suspend option in the internal EEPROM.
iii) The PWREN# pin should be used to switch the power to the external circuitry.
iv) For USB high-power bus powered device (one that consumes greater than 100mA, and up to 500mA of current
v) For 3.3V power controlled circuits the VCCIO pin must not be powered down with the external circuitry (the
FT245R USB UART I.C. Datasheet Version 1.05
The logic to be controlled must have its own reset circuitry so that it will automatically reset itself when power is re-
applied on coming out of suspend.
from the USB bus), the power consumption of the device should be set in the max power field in the internal
EEPROM. A high-power bus powered device must use this descriptor in the internal EEPROM to inform the
system of its power requirements.
PWREN# signal gets its VCC supply from VCCIO). Either connect the power switch between the output of the
3.3V regulator and the external 3.3V logic or power VCCIO from the 3V3OUT pin of the FT245R.
7.3 USB Bus Powered with Power Switching Configuration
SHIELD
5
1
2
3
4
10nF
100nF
GND
+
Ferrite
Bead
4.7uF
GND
+
5V VCC
P-Channel Power
5V VCC
s
MOSFET
g
d
1k
0.1uF
GND
100nF
Soft Start
Circuit
VCC
USBDM
USBDP
3V3OUT
VCCIO
RESET#
OSCI
OSCO
NC
NC
© Future Technology Devices International Ltd. 2005
A
G
N
D
0.1uF
FT245R
G
N
D
G
N
D
GND
Switched 5V Power
G
N
D
to External Logic
T
E
S
T
PWREN#
RXF#
TXE#
WR#
RD#
D0
D1
D2
D3
D4
D5
D6
D7

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