SN74HC138N Detailed explanation of pin function specifications and circuit principle instructions
The component you're referring to, SN74HC138N, belongs to Texas Instruments (TI), a leading semiconductor manufacturer.
SN74HC138N Pin Function Specifications and Circuit Principle Instructions
This is a 3-to-8 line decoder/demultiplexer, typically used for applications that need binary decoding for multiple outputs. It belongs to the 74HC family (High-speed CMOS), offering low Power consumption and high-speed operation.
Package and Pinout Overview
The SN74HC138N is commonly available in an 18-pin Dual In-line Package (DIP), which is a through-hole package type. Pin Count: 18 pins.Pin Function and Specifications
Here's a detailed table of all the 18 pins, with corresponding functionality:
Pin Number Pin Name Pin Function 1 A0 Input pin for the least significant bit (LSB) of the 3-bit binary address (A0). 2 A1 Input pin for the middle bit of the 3-bit binary address (A1). 3 A2 Input pin for the most significant bit (MSB) of the 3-bit binary address (A2). 4 G1 Active LOW enable input for output selection (also known as chip enable). 5 G2A Active LOW enable input that works with G2B for output enable control. 6 G2B Active LOW enable input that works with G2A for output enable control. 7 Y0 Active LOW output pin 0 (Y0), driven low when corresponding address (A0, A1, A2) is selected. 8 Y1 Active LOW output pin 1 (Y1), driven low when corresponding address is selected. 9 Y2 Active LOW output pin 2 (Y2), driven low when corresponding address is selected. 10 Y3 Active LOW output pin 3 (Y3), driven low when corresponding address is selected. 11 Y4 Active LOW output pin 4 (Y4), driven low when corresponding address is selected. 12 Y5 Active LOW output pin 5 (Y5), driven low when corresponding address is selected. 13 Y6 Active LOW output pin 6 (Y6), driven low when corresponding address is selected. 14 Y7 Active LOW output pin 7 (Y7), driven low when corresponding address is selected. 15 VCC Power supply pin (typically +5V). 16 GND Ground pin (0V). 17 /OE (Output Enable) Active LOW signal used to enable or disable the outputs, connected to G2A/G2B for enabling output. 18 /GND Internal ground. This pin is typically not externally used for user connections.Principle of Operation
The SN74HC138N operates by decoding a 3-bit binary input and selecting one of the eight output lines (Y0 through Y7). The outputs are active LOW, meaning that when a particular output is selected, it will be driven low, while the other outputs will remain in a high-impedance state. It requires proper logic level signals at A0, A1, and A2 for address selection, while G1, G2A, and G2B serve as enable pins to activate or disable the outputs.18-Pin Package Functional Description
The enable pins (G1, G2A, G2B) are used to control whether the outputs are active or in high impedance. When all enable pins are LOW, the corresponding outputs (Y0 to Y7) are active based on the address inputs. If any enable pin is HIGH, the outputs are disabled. The address pins (A0, A1, A2) select which one of the outputs (Y0 to Y7) is activated, by decoding the binary value on these pins. Outputs (Y0 to Y7) are active LOW, meaning they will output 0 when selected and stay in high-impedance (disabled) state otherwise.20 Common FAQ for SN74HC138N
Here are 20 frequently asked questions regarding the SN74HC138N:
Q: What is the primary function of the SN74HC138N? A: The SN74HC138N is a 3-to-8 line decoder/demultiplexer used to decode a 3-bit address into one of eight active LOW output lines.
Q: How many pins does the SN74HC138N have? A: The SN74HC138N has 18 pins.
Q: What is the voltage range for the SN74HC138N? A: The operating voltage range for SN74HC138N is typically from 2V to 6V.
Q: Can the outputs of the SN74HC138N be active HIGH? A: No, the outputs (Y0-Y7) are active LOW, meaning they are LOW when selected and high-impedance when not.
Q: How many address pins are there in the SN74HC138N? A: There are 3 address pins: A0, A1, and A2.
Q: How do I enable the outputs of the SN74HC138N? A: To enable the outputs, all enable pins (G1, G2A, and G2B) must be LOW.
Q: What happens if any of the enable pins are HIGH? A: If any enable pin is HIGH, the outputs will be disabled and placed in a high-impedance state.
Q: What type of logic family does the SN74HC138N belong to? A: The SN74HC138N belongs to the High-speed CMOS (HC) logic family.
Q: What is the maximum input voltage for the address pins? A: The input voltage for address pins should be within the supply voltage range, typically from 0V to 5V.
Q: Can the SN74HC138N be used for any addressable demultiplexing system? A: Yes, it can be used wherever there is a need to select one of eight outputs based on a 3-bit address.
Q: How much current does the SN74HC138N consume? A: The current consumption depends on the operating voltage, but it typically draws about 4mA in active operation.
Q: What is the function of the /OE pin on the SN74HC138N? A: The /OE pin is used to enable or disable the output lines. When LOW, outputs are enabled; when HIGH, outputs are disabled.
Q: What is the logic level of the output pins? A: The output pins are active LOW, meaning they output a logical 0 when selected.
Q: What happens when the input address is set to 7 (A2 = 1, A1 = 1, A0 = 1)? A: The output Y7 will be driven LOW, while all other outputs will be in a high-impedance state.
Q: Is the SN74HC138N available in other package types? A: Yes, the SN74HC138N is available in various package types like SOIC, TSSOP, and others.
Q: How can I use the SN74HC138N to build a memory address decoder? A: You can use the SN74HC138N to select one of eight memory locations based on a 3-bit address input.
Q: Can the SN74HC138N be used in combination with other decoders? A: Yes, it can be chained with other decoders to decode more than 3 bits.
Q: Does the SN74HC138N have any built-in protection against short circuits? A: While it has internal protection, it's always good practice to follow recommended operating conditions to prevent damage.
Q: How fast can the SN74HC138N operate? A: The SN74HC138N operates at speeds up to 6 MHz at Vcc = 5V.
Q: Can the SN74HC138N be used in applications with multiple active outputs? A: No, it only allows one active output at a time, with the others in high-impedance states.
This detailed explanation should cover the basic function, pinout, and common FAQs regarding the SN74HC138N decoder IC. Let me know if you need further elaboration on any point!
