FS401 Datasheet, PDF (100/104 Pages) List of Unclassifed Manufacturers – PC to TV Video Scan Converters

FS401, FS403
PRODUCT SPECIFICATION
REV. NO. 1.7
For applications with more than one supply, combinations of the above two circuits can be used.
However, the simplest approach to this problem is to limit the loading on the SIO bus when possible.
When this is not possible, some of the SIO passive loads can be replaced with active ones. This will
increase the SIO access speed without increasing the SIO output low drive current.
In lightly loaded SIO busses (where V_OL is easily reached), a single MOSFET can be used for translation
on the SIO SDA line (Since the FS400’s input for SCL is 5 Volt tolerant, no additional parts are required
on that input). Pull-ups on both supply sides assure that the output on each device can reach its
corresponding upper limit. The pass gate (Q1) provides a low impedance connection during the low
switching voltage.
+3.3V
+5V
FS400
OC Output
R1
R2
10K
10K
Q1
5 Volt Device
OC Output
Figure 27. SIO (Open Collector) Translation using a MOSFET
Q1 = BSS138
Q1 also provides isolation when the 3.3 Volt power to the FS400 is removed. The pass gate (Q1) gate to
source voltage is negative and the bulk diode is off. This effectively removes the FS400’s Serial Data line
from the SIO bus system and allows the higher voltage SIO section to operate normally.
JANUARY 24, 2007
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