VCC

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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Copyright © 1985–2016, Texas Instruments Incorporated

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 VCC 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

VCC 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 VCC

(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