Understand the Current Consumption of an IC in its Datasheet

In summary, the conversation discusses the current consumption of an integrated circuit (IC) and the various factors that affect it. The IC has a minimum current consumption of 80uA and a maximum of 50mA. The 80uA is achieved at an ambient temperature of 25°C, and the maximum is due to the internal construction of the IC. The IC consumes 4.08mA during operation, with the remaining output pins reducing the consumption to -24mA. The 50mA limit is the maximum current that can flow through the VCC or GND pins before causing internal damage to the device. The conversation also includes the use of technical terms and the input and output characteristics of the IC.
  • #1
mheruian
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Hi, I'm new here and maybe this is the best section where I could need help :) I've been interested in electronics lately (not schooling anymore, more on self-study, but I'm not that smart, just a dedicated one and i can't understand everything right through). I don't have any equipment yet like osci, etc. Then I thought of doing mathematics on the physics side of electronic components like integrated circuits (IC) since even though ideal, math in some percentage of little marginal error, result should reflect close to reality (simple math is what I rely on).

Here's where I am at, I'm trying to know the current consumption (minimum and max) of this IC (http://www.ti.com/lit/ds/symlink/sn74hct138.pdf). Upon reading the documentation, I am at first thought it was easy since 80uA was brought up in the description but skimming on the electrical characteristics (image link below) looks like this is the max current consumption when there is no output current (Io = 0) on its decoding output lines.

https://drive.google.com/file/d/1b4nBmQ8Yd2g5oYXemnUTcV-VD0B0YhtM/view

That means the IC is in idle state right consuming current just for powering it self up and not for output/decode operation? Then i found the continuous current output and continuous current through VCC or GND? I got confused but still proceeded.

Here's what I computed for getting current consumption for output operation:

Iconsume = Icc + IOL
Iconsume = 80uA + 4mA
Iconsume = 80uA + 4mA
Iconsume = 4.08mA

Imin = 1000nA or 1uA (this is idle state also?)

Imax = 50mA (Maybe an addition how did they get this?)

If I can determine these currents in the 3 states of the IC, I can now know the power consumption of the IC. I hope someone could verify this or correct me.
 
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  • #2
mheruian said:
That means the IC is in idle state right consuming current just for powering it self up and not for output/decode operation?
Correct.
mheruian said:
Here's what I computed for getting current consumption for output operation:

Iconsume = Icc + IOL
Iconsume = 80uA + 4mA
Iconsume = 80uA + 4mA
Iconsume = 4.08mA
Note that the 4mA is for each output pin.

mheruian said:
Imax = 50mA
That is the current thru the VCC or GND pins that, if exceeded, will cause internal damage to the device. That limitation is indicated by the table heading on the Data Sheet of "absolute maximum ratings..."

mheruian said:
Imin = 1000nA or 1uA (this is idle state also?)
That is the most current that will flow into or out of any Input when that input is at either VCC or GND.

NOTE: The ∆ICC (in electrical characteristics... table on pg4) shows that if an input is at 0.5V or 2.4V then the supply current will increase by 2.9mA for each input at that voltage. This is due to the internal construction of the IC. For each input, there are two transistors in series that connect to VCC and GND. When an input is at either 0.5V or 2.4V both of the transistors ar turned ON, supplying a direct path between VCC and GND.

Cheers, and welcome to the world of Electronics,
Tom
 
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  • #3
Thanks a lot Tom.G ! :D just got home and did some familiarization on technical terms. I hope I'm using the right technical terms.

Tom.G said:
mheruian said:
That means the IC is in idle state right consuming current just for powering it self up and not for output/decode operation?
Correct.

Ok? so that means its current consumption while no operation would be 8uA (25°C ambient temperature) up to 80uA (if SN74 IC was used), this 80uA will be achieved if temperature is either more than OR less than 25°C? Sorry if I can't pretty much perceive it since I'm new to this, datasheets are quite not specific for my understanding haha!

Tom.G said:
Note that the 4mA is for each output pin.

Oh I see, right now, I'm looking again at the datasheet at the Function Table pg.2 - So since there can only be 1 IOL (1 Low output pin) on every input combination, Iconsume while on operation is always 4.08mA? but this consumption will be decrease since the 7 remaining output pin would be High - IOH, that'll be:

Total IOH = -4mA x 7
Total IOH = -28mA
Total Iconsume = 4.08mA - 28mA
Total Iconsume = -24mA (this'll be like no current was consume or power used?)

Do i get that right?

Tom.G said:
That is the current thru the VCC or GND pins that, if exceeded, will cause internal damage to the device. That limitation is indicated by the table heading on the Data Sheet of "absolute maximum ratings..."

Ok? so like power surge? just this day, I had a talk on a colleague of mine at school on old days. Well, he is smart that's why I ask him some questions too though he is not into electronic stuff (he has the highest grade on physics on our class that time). I show him the datasheet and ask a lot of stuffs then he said that "load will only consume a current that it needs with respect to its total resistance...". That made me think, how come such surge could happen if the load (circuit, appliances, etc said by my colleague) will only use current that it needs? some resistors on the load worn out so current it takes increases??

Tom.G said:
That is the most current that will flow into or out of any Input when that input is at either VCC or GND.

Got it! so that's the maximum Iinput that applies on all the ICs pins? I'm seeing this Test Condition "VI = VCC or 0", so even you input 0 volts on any pins, it will still consume current? why is that? isn't 0 volts = 0 charge / current flow?

Tom.G said:
NOTE: The ∆ICC (in electrical characteristics... table on pg4) shows that if an input is at 0.5V or 2.4V then the supply current will increase by 2.9mA for each input at that voltage. This is due to the internal construction of the IC. For each input, there are two transistors in series that connect to VCC and GND. When an input is at either 0.5V or 2.4V both of the transistors ar turned ON, supplying a direct path between VCC and GND.

Ok, i got this one as clear as day. Thanks for helping me understand it :) Quite having some goose bump since I'm excited to know a lot at the same time, my mind hurts on some confusions i don't get. BTW, thanks for the warm welcome on the electronics world!

:dademyday:
Mheruian
 
  • #4
mheruian said:
Ok? so that means its current consumption while no operation would be 8uA (25°C ambient temperature) up to 80uA (if SN74 IC was used), this 80uA will be achieved if temperature is either more than OR less than 25°C? Sorry if I can't pretty much perceive it since I'm new to this, datasheets are quite not specific for my understanding haha!
Generally (almost always), current will increase with increased temperature and decrease with decreased temperature Also note that the SN54 series has 160μA maximum current.
mheruian said:
Oh I see, right now, I'm looking again at the datasheet at the Function Table pg.2 - So since there can only be 1 IOL (1 Low output pin) on every input combination, Iconsume while on operation is always 4.08mA? but this consumption will be decrease since the 7 remaining output pin would be High - IOH, that'll be:

Total IOH = -4mA x 7
Total IOH = -28mA
Total Iconsume = 4.08mA - 28mA
Total Iconsume = -24mA (this'll be like no current was consume or power used?)

Do i get that right?
Not quite. No subtraction of the supply current occurs. The current that the chip itself uses remains 8μA. (at 25°C)

electrical characteristics... table pg4:
Lets look at VOH first. What the data sheet indicates is that any output that is High will be able to supply 4mA from VCC to a load connected to Ground, and will keep the output voltage to at least 3.98V.

Now the next datasheet line, VOL, says: Any output that is Low will be able to sink 4mA to GND from a load connected to VCC and will keep the output voltage at or below 0.26V.

This table shows the "normal" operating range of the IC. You notice that the signal pins are specified for both voltage and current values. This is to ensure that they will operate correctly when connected to other chips from the same logic family (74HCT in this case).

mheruian said:
That made me think, how come such surge could happen if the load (circuit, appliances, etc said by my colleague) will only use current that it needs?

The absolute maximum ratings...table pg3, show what the IC is physically capable of without damage. Perhaps instead of driving another IC, you want to drive some LEDs. The table shows that each output pin can supply ±25mA, which would be plenty to drive an LED. You could connect an LED to each output.
But, the maximum current thru either VCC or GND is 50mA. so you couldn't have more than 2 LEDs on at once.

Also notice that in this table that there is no statement of what the voltage will be at higher load currents. So if you draw higher currents there is no guarantee the IC output voltage is sufficient to drive another IC.

mheruian said:
Got it! so that's the maximum Iinput that applies on all the ICs pins? I'm seeing this Test Condition "VI = VCC or 0", so even you input 0 volts on any pins, it will still consume current? why is that? isn't 0 volts = 0 charge / current flow?

Internal components of the IC connect to both VCC and GND so there is a path to both. As an example consider two resistors in series connected between VCC and GND. The common point of the resistors will be at some voltage and will draw current thru an external connection to either Power or Ground.

Whew! You brain exploding yet? :smile:
Tom
 
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  • #5
Hi Mr.Tom!

Thanks a lot for always keeping this newbie lad being informed. I appreciate all the efforts and i learn a lot :)

Tom.G said:
Whew! You brain exploding yet? :smile:
:confused: it already did ! hahaha! I'm trying to imagine and even draw sketches of your every explanation so i can get this right.

Tom.G said:
electrical characteristics... table pg4:
Lets look at VOH first. What the data sheet indicates is that any output that is High will be able to supply 4mA from VCC to a load connected to Ground, and will keep the output voltage to at least 3.98V.

(After searching and asking others what load really means, it could be represented by resistor because load means something that has resistance since it consumes current they say :nb))
NebBTqC.jpg

Did I get that right? (Do i look desperate with this one? haha)

Tom.G said:
Now the next datasheet line, VOL, says: Any output that is Low will be able to sink 4mA to GND from a load connected to VCC and will keep the output voltage at or below 0.26V.

005kjuH.jpg

Based from the previous sketch of mine and judging the datasheet's value and direction/flow of current?? why i feel -4mA value is +4mA? do i compute them right? :H Should I consider that 4mA an addition and not subtract to the current consumption of the IC since current flow is sinking inside IC?

Tom.G said:
This table shows the "normal" operating range of the IC. You notice that the signal pins are specified for both voltage and current values. This is to ensure that they will operate correctly when connected to other chips from the same logic family (74HCT in this case).

Well, this one is a good thing! glad you had explained it to me :D since this day, i saw some electronic students passing by and did some quick question interview (desperate one :DD) with them about this computation thing specially when it was about IC to IC stuffs. They told me that their school only teaches voltage, current, power, etc computation on resistors, caps and inductors but not on ICs so they are not pretty sure about my question (maybe not yet covered). So based on what I learn here, below are some sketches.

HGwgklu.jpg


Is the above sketch is correct?

jbuiIUw.jpg


how about this one?? :oldconfused: got confused on sinking stuffs

Tom.G said:
The absolute maximum ratings...table pg3, show what the IC is physically capable of without damage. Perhaps instead of driving another IC, you want to drive some LEDs. The table shows that each output pin can supply ±25mA, which would be plenty to drive an LED. You could connect an LED to each output.
But, the maximum current thru either VCC or GND is 50mA. so you couldn't have more than 2 LEDs on at once.

Also notice that in this table that there is no statement of what the voltage will be at higher load currents. So if you draw higher currents there is no guarantee the IC output voltage is sufficient to drive another IC.
Oh ok, :D if loads are not LED but other ICs, i should base these specs like IC1 output current is able to fit on IC2's input current rating?

Tom.G said:
Internal components of the IC connect to both VCC and GND so there is a path to both. As an example consider two resistors in series connected between VCC and GND. The common point of the resistors will be at some voltage and will draw current thru an external connection to either Power or Ground.

Ok :D like this two sketches below??

Y5lNESn.jpg

88DH4N8.jpg


I'm learning a lot right? :oldlaugh: Well, seriously, I'm grateful :partytime: thank you very much for being supportive on my study.
 

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  • #6
mheruian said:
I'm learning a lot right? :oldlaugh:
Yup! Enough that I can start taking shortcuts in answering your questions without much likelyhood of confusing you. :wink:

These sketches pertain to the first two and last two sketches of your post. Note that the output voltages are a little different than what you had. The 80μA ICC (Iconsume in the sketches) is the maximum over the temperature range, so I used the worst case Output voltages that apply over the temperature range.
Untitled-1.jpg
Untitled-2.jpg


Edit: RATS, those images didn't show up. I am trying again.
...Ahhh... Success!
end Edit:

Your 3rd and 4th sketches, the ones with two ICs, need to show that the current flow (signals) between the ICs won't exceed the minimum of the current either needed by the input(s) or available from the output(s). For instance if an Iinput only draws (needs) 1000nA (1uA) there will not be 4mA flowing thru the Output that feeds it. Since the Output can reliably supply up to 4mA, you could connect it to 4000 inputs! Well, not really, you run into several different problems trying to do that. I'm just using that 4000 number as a worstcase possibility.
 

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Related to Understand the Current Consumption of an IC in its Datasheet

1. What is the significance of understanding the current consumption of an IC?

The current consumption of an IC, or integrated circuit, is an important specification to consider when designing electronic circuits. It determines the amount of power that the IC will draw from the power supply, which can impact the overall performance and efficiency of the circuit.

2. How is the current consumption of an IC typically measured?

The current consumption of an IC is usually measured in units of milliamps (mA) or microamps (μA). It can be measured using a multimeter or a specialized current measurement tool.

3. Why is the current consumption of an IC listed as a range in its datasheet?

The current consumption of an IC can vary based on a number of factors, such as operating temperature, input voltage, and load conditions. Therefore, the datasheet will typically list a range of values to account for these variables.

4. How can the current consumption of an IC be minimized?

To minimize the current consumption of an IC, designers can use techniques such as optimizing the circuit layout, selecting low-power components, and implementing power-saving modes. Additionally, choosing an IC with a lower current consumption specification can also help reduce overall power consumption.

5. Can the current consumption of an IC change over time?

Yes, the current consumption of an IC can change over time due to factors such as aging of the components and environmental conditions. It is important for designers to take these potential changes into account when selecting and designing with an IC.

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