Overview
The SN74HCT138NS is a 3-Line to 8-Line Decoder/Demultiplexer produced by Texas Instruments. This device is designed for high-performance memory-decoding or data-routing applications that require very short propagation delay times. It is particularly useful in high-performance memory systems where it can minimize the effects of system decoding. When used with high-speed memories that have fast enable circuits, the delay times of these decoders and the enable time of the memory are typically less than the memory's access time, making the system delay introduced by the decoders negligible.
Key Specifications
| Parameter | Unit | Min | Max | |
|---|---|---|---|---|
| Operating Voltage Range (VCC) | V | 4.5 | 5 | 5.5 |
| High-Level Input Voltage (VIH) | V | 2 | - | 2 |
| Low-Level Input Voltage (VIL) | V | 0.8 | - | 0.8 |
| Output Voltage (VO) | V | 0 | - | VCC |
| Propagation Delay Time (tpd) | ns | 17 | - | 32 |
| Input Transition Rise/Fall Time (tt) | ns | 11 | - | 20 |
| Supply Current (ICC) | μA | 8 | - | 80 |
| Operating Free-Air Temperature (TA) | °C | -40 | - | 85 |
| Junction-to-Ambient Thermal Resistance (RθJA) | °C/W | 64 | - | - |
Key Features
- Operating voltage range of 4.5 V to 5.5 V
- Outputs can drive up to 10 LSTTL loads
- Low power consumption, with a maximum supply current (ICC) of 80 μA
- Typical propagation delay time (tpd) of 17 ns
- ±4-mA output drive at 5 V
- Low input current of 1 μA max
- Inputs are TTL-Voltage compatible
- Designed specifically for high-speed memory decoders and data transmission systems
- Incorporate three enable inputs to simplify cascading and/or data reception
Applications
The SN74HCT138NS is ideal for high-performance memory-decoding or data-routing applications. It is particularly useful in:
- High-speed memory systems where short propagation delay times are critical.
- Data transmission systems that require fast and reliable data routing.
- Cascading applications where multiple decoders need to be connected without external gates or inverters.
- Demultiplexing applications where an enable input can be used as a data input.
Q & A
- What is the operating voltage range of the SN74HCT138NS?
The operating voltage range is from 4.5 V to 5.5 V.
- How many LSTTL loads can the outputs of the SN74HCT138NS drive?
The outputs can drive up to 10 LSTTL loads.
- What is the typical propagation delay time of the SN74HCT138NS?
The typical propagation delay time is 17 ns.
- What is the maximum supply current (ICC) of the SN74HCT138NS?
The maximum supply current is 80 μA.
- Are the inputs of the SN74HCT138NS TTL-Voltage compatible?
Yes, the inputs are TTL-Voltage compatible.
- How many enable inputs does the SN74HCT138NS have?
The device has three enable inputs.
- What is the junction-to-ambient thermal resistance (RθJA) of the SN74HCT138NS in the SO package?
The junction-to-ambient thermal resistance is 64 °C/W.
- What is the recommended bypass capacitor for the power supply of the SN74HCT138NS?
A 0.1-μF capacitor is recommended, and it is acceptable to parallel multiple bypass caps to reject different frequencies of noise.
- How should unused inputs of the SN74HCT138NS be handled?
Unused inputs must be held at VCC or GND to ensure proper device operation.
- In what types of applications is the SN74HCT138NS particularly useful?
The device is particularly useful in high-speed memory systems and data transmission systems requiring fast and reliable data routing.
