What is the maximum output current of a logic gate at 5V VCC?

In summary: I wanted to create a NOT gate using a transistor. But I don't need it now because I have an ic for itSure
  • #1
TheRedDevil18
408
1
Hi, I have this logic gate
http://www.ti.com/lit/ds/symlink/sn54hc32.pdf

I am using 5V as my VCC. In the datasheet it says that the output current at 6V is 5.2mA. My question is, Is that the max current that it can output ?
 
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  • #2
TheRedDevil18 said:
My question is, Is that the max current that it can output ?
For sure not.
http://www.nxp.com/documents/user_manual/HCT_USER_GUIDE.pdf (page 34)
You can drawn more current but Voh voltage will drop bellow Vih (High-level input voltage ), so the next gate will not be able to properly recognize the logic state at his input.
 
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  • #3
Jony130 said:
For sure not.
http://www.nxp.com/documents/user_manual/HCT_USER_GUIDE.pdf (page 34)
You can drawn more current but Voh voltage will drop bellow Vih (High-level input voltage ), so the next gate will not be able to properly recognize the logic state at his input.

Ok, is there any way to know by how much it might drop ?, I am feeding it to the base of a transistor
 
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  • #4
How much base current do you need? Also if you drive a BJT base only then you do not have to worry about VIh any more because the BJT is not a logic circuit so you do not have to meet the logic level regiments. Also we can find in datasheet the info that Io_max = 20mA
https://en.wikipedia.org/wiki/Logic_level#Logic_voltage_levels
 
  • #5
Jony130 said:
How much base current do you need? Also if you drive a BJT base only then you do not have to worry about VIh any more because the BJT is not a logic circuit so you do not have to meet the logic level regiments. Also we can find in datasheet the info that Io_max = 20mA
https://en.wikipedia.org/wiki/Logic_level#Logic_voltage_levels

Assuming the output voltage from the ic is 5V which I used to calculate my base resistance. The current would be about 5.5mA
 
  • #6
No worries here the gate will survive this.
As we can see from this characteristic
Voh.png


The voltage drop across the gate output will not be larger than 0.8V and typically it will be around 0.3V.
 
  • #7
Jony130 said:
No worries here the gate will survive this.
As we can see from this characteristic
View attachment 98723

The voltage drop across the gate output will not be larger than 0.8V and typically it will be around 0.3V.

Thanks, So I can assume the output voltage from the gate and hence the voltage to the base of my transistor will be about 4.7V ?

Also, from the same datasheet, how much current does the ic draw when one of the pins is held high ?, I want to calculate a pull up resistor to ensure that the pin gets close to 5V as possible. I read around and they about 5k to 10k should be fine
 
  • #8
TheRedDevil18 said:
So I can assume the output voltage from the gate and hence the voltage to the base of my transistor will be about 4.7V ?
Yes.
TheRedDevil18 said:
Also, from the same datasheet, how much current does the ic draw when one of the pins is held high ?
The current consumption will depend on the load resistance. Because CMOS circuit in static do not burned any power. Only the load will consume power from power supply.
TheRedDevil18 said:
Also, from the same datasheet, how much current does the ic draw when one of the pins is held high ?, I want to calculate a pull up resistor to ensure that the pin gets close to 5V as possible. I read around and they about 5k to 10k should be fine
Do you really want to put a pull-up resistor at the gate output? Why ?
 
  • #9
Jony130 said:
Yes.

The current consumption will depend on the load resistance. Because CMOS circuit in static do not burned any power. Only the load will consume power from power supply.

Do you really want to put a pull-up resistor at the gate output? Why ?

I wanted to create a NOT gate using a transistor. But I don't need it now because I have an ic for it
 
  • #10
Can I suggest you post a sketch of this bit of your finished circuit?
 

Related to What is the maximum output current of a logic gate at 5V VCC?

1. What is a logic gate output current?

A logic gate output current refers to the amount of electrical current that is output from a logic gate when a specific input is received. Logic gates are electronic devices that perform logical operations based on their inputs, and the output current is a representation of the logic gate's response to those inputs.

2. How is the output current of a logic gate measured?

The output current of a logic gate is typically measured in units of amperes (A) or milliamperes (mA) using a multimeter or other electrical measuring device. It is important to note that the output current can vary depending on the specific type of logic gate and the input signals being used.

3. What factors affect the output current of a logic gate?

Several factors can affect the output current of a logic gate, including the type of logic gate (such as AND, OR, NOT, etc.), the input voltage levels, the power supply voltage, and the load resistance connected to the output. These factors can impact the logic gate's ability to switch and maintain a stable output current.

4. How does the output current of a logic gate relate to its input signals?

The output current of a logic gate is directly influenced by the input signals it receives. For example, in an AND gate, the output current will only be high if both of its inputs are high. In an OR gate, the output current will be high if either or both of its inputs are high. The specific logic operation of the gate determines the relationship between the input signals and the output current.

5. Can the output current of a logic gate be changed?

Yes, the output current of a logic gate can be changed by adjusting the input signals or by altering the circuit components connected to the gate. For example, changing the input voltage levels or the load resistance can affect the output current. Additionally, using different types of logic gates or combining multiple gates in a circuit can also impact the output current.

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