Datasheet

V
CC
Unused Input
Input
Output Output
Input
Unused Input
17
SN54LS240 , SN54LS241 , SN54LS244 , SN54S240 , SN54S241 , SN54S244
SN74LS240 , SN74LS241 , SN74LS244 , SN74S240 , SN74S241 , SN74S244
www.ti.com SDLS144D –APRIL 1985–REVISED OCTOBER 2016
Product Folder Links: SN54LS240 SN54LS241 SN54LS244 SN54S240 SN54S241 SN54S244 SN74LS240
SN74LS241 SN74LS244 SN74S240 SN74S241 SN74S244
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10 Power Supply Recommendations
The power supply can be any voltage between the minimum and maximum supply voltage rating located in
Recommended Operating Conditions. Each V
CC
pin must have a good bypass capacitor to prevent power
disturbance. For devices with a single supply, TI recommends a 0.1-µF bypass capacitor. If there are multiple
V
CC
pins, TI recommends a 0.01-µF or 0.022-µF bypass capacitors for each power pin. It is acceptable to parallel
multiple bypass capacitors to reject different frequencies of noise. Two bypass capacitors of value 0.1 µF and
1 µF are commonly used in parallel. For best results, install the bypass capacitor(s) as close to the power pin as
possible.
11 Layout
11.1 Layout Guidelines
When using multiple bit logic devices, inputs must not be left floating. In many applications, some channels of the
SNx4LS24x, SNx4S24x are unused, and thus must be terminated properly. Because each transceiver channel
pin can be either an input or an output, they must be treated as both when being terminated. Ground or V
CC
(whichever is more convenient) can be used to terminate unused inputs; however, each unused channel should
be terminated to the same logic level on both the A and Y side. For example, in Figure 27 unused channels are
terminated correctly with both sides connected to the same voltage, while channel 8 is terminated incorrectly with
each side being tied to a different voltage. The G input is also unused in this example, and is terminated directly
to ground to permanently enable all outputs.
11.2 Layout Example
Figure 27. Example Demonstrating How to Terminate Unused Inputs and Channels of a Transceiver