These Schottky-clamped TTL MSI circuits are designed to be used in high-performance memory decoding or data-routing applications requiring very short propagation delay times. In high-performance memory systems, these decoders can be used to minimize the effects of system decoding. When employed with high-speed memories utilizing a fast enable circuit, the delay times of these decoders and the enable time of the memory are usually less than the typical access time of the memory. This means that the effective system delay introduced by the Schottky-clamped system decoder is negligible.
The 'LS138, SN54S138, and SN74S138A decode one of eight lines dependent on the conditions at the three binary select inputs and the three enable inputs. Two active-low and one active-high enable inputs reduce the need for external gates or inverters when expanding. A 24-line decoder can be implemented without external inverters and a 32-line decoder requires only one inverter. An enable input can be used as a data input for demultiplexing applications.
All of these decoder/demultiplexers feature fully buffered inputs, each of which represents only one normalized load to its driving circuit. All inputs are clamped with high-performance Schottky diodes to suppress line-ringing and to simplify system design.
The SN54LS138 and SN54S138 are characterized for operation over the full military temperature range of -55°C to 125°C. The SN74LS138 and SN74S138A are characterized for operation from 0°C to 70°C.
| Type | Title | Date | ||
|---|---|---|---|---|
| * | Data sheet | 3-Line To 8-Line Decoders/Demultiplexers datasheet | 01 Mar 1988 | |
| * | SMD | SN54LS138 SMD 76005012A | 21 Jun 2016 | |
| Selection guide | Logic Guide (Rev. AB) | 12 Jun 2017 | ||
| Application note | Understanding and Interpreting Standard-Logic Data Sheets (Rev. C) | 02 Dec 2015 | ||
| User guide | LOGIC Pocket Data Book (Rev. B) | 16 Jan 2007 | ||
| Application note | Semiconductor Packing Material Electrostatic Discharge (ESD) Protection | 08 Jul 2004 | ||
| Application note | TI IBIS File Creation, Validation, and Distribution Processes | 29 Aug 2002 | ||
| Application note | Designing With Logic (Rev. C) | 01 Jun 1997 | ||
| Application note | Designing with the SN54/74LS123 (Rev. A) | 01 Mar 1997 | ||
| Application note | Input and Output Characteristics of Digital Integrated Circuits | 01 Oct 1996 | ||
| Application note | Live Insertion | 01 Oct 1996 |
For additional terms or required resources, click any title below to view the detail page where available.
| Package | Pins | CAD symbols, footprints & 3D models |
|---|---|---|
| CDIP (J) | 16 | Ultra Librarian |
| CFP (W) | 16 | Ultra Librarian |
| LCCC (FK) | 20 | Ultra Librarian |
Content is provided "as is" by TI and community contributors and does not constitute TI specifications. See terms of use.
If you have questions about quality, packaging or ordering TI products, see TI support.