Difference between input current and supply current

OBW0549

Joined Mar 2, 2015
3,566
In the table 6.5, there are two parameters namely Ii and Icc. Input current and supply current. I would want to understand the difference between the two terms?
Ii refers to the current flowing into or out of the gate inputs, mainly consisting of leakage currents thru the input protection diodes plus any gate leakage from the MOSFETs comprising the gates.

Icc refers to the current drawn by the device from its Vcc supply-- that is, its operating current.
 

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Electronic_Maniac

Joined Oct 26, 2017
253
Ii refers to the current flowing into or out of the gate inputs, mainly consisting of leakage currents thru the input protection diodes plus any gate leakage from the MOSFETs comprising the gates.

Icc refers to the current drawn by the device from its Vcc supply-- that is, its operating current.
Thank you. But why do the gates need current?
 

dl324

Joined Mar 30, 2015
13,141
In the table 6.5, there are two parameters namely Ii and Icc. Input current and supply current.
Pay attention to the subscripts.

Ii is usually for input.

Icc stands for collector current and is a misnomer in CMOS because there are no collectors. It's the current drawn by all of the devices.
EDIT: fixed missing space.
 
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dl324

Joined Mar 30, 2015
13,141
Here's part of the glossary section from the 1981 TI TTL Databook. It's for bipolar, but some are still applicable to CMOS. I'll see if I have one for CMOS.
 

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OBW0549

Joined Mar 2, 2015
3,566
Some further thoughts (perhaps more than you wanted to know, but I thought I'd throw it in...):

So far, the current consumption we've mainly been talking about is static current consumption-- that is, current that flows even when the inputs and outputs of a device aren't changing state.

But there's also dynamic current consumption, which @dl324 alluded to in post #5, which occurs when inputs and outputs are changing state. This current can be many times the magnitude of the static current, and it's the reason why CMOS circuits typically draw operating current in proportion to their clock rate.

If you want to delve deeper into the matter, the attached .pdf from Texas Instruments goes into detail and introduces the concepts of transient power consumption, capacitive-load power consumption, and power dissipation capacitance.

Enjoy, if you're interested...
 

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Thread Starter

Electronic_Maniac

Joined Oct 26, 2017
253
Some further thoughts (perhaps more than you wanted to know, but I thought I'd throw it in...):

So far, the current consumption we've mainly been talking about is static current consumption-- that is, current that flows even when the inputs and outputs of a device aren't changing state.

But there's also dynamic current consumption, which @dl324 alluded to in post #5, which occurs when inputs and outputs are changing state. This current can be many times the magnitude of the static current, and it's the reason why CMOS circuits typically draw operating current in proportion to their clock rate.

If you want to delve deeper into the matter, the attached .pdf from Texas Instruments goes into detail and introduces the concepts of transient power consumption, capacitive-load power consumption, and power dissipation capacitance.

Enjoy, if you're interested...
Thank you. I have been reading about these terms and I have a few doubts.

The static current consumption that you are talking, is also know as Quiescent current, right?
From what I have read, Quiescent current is the current which is used to turn the device on (to just power the internal circuitry of the device) and when no current is drawn by the load.
So, Quiescent current is also know as the static current which you are describing, am I right?
Are these terms used interchangeably?

And from what I have read, dynamic current consumption will be the the static (quiescent) current + the current drawn by the load during operation, right?

Thanks.
 

OBW0549

Joined Mar 2, 2015
3,566
The static current consumption that you are talking, is also know as Quiescent current, right?
From what I have read, Quiescent current is the current which is used to turn the device on (to just power the internal circuitry of the device) and when no current is drawn by the load.
So, Quiescent current is also know as the static current which you are describing, am I right?
Yes, pretty much; although I usually use the term "static current" when talking about CMOS logic devices, and "quiescent current" when discussing analog devices such as voltage regulators.

Are these terms used interchangeably?
They can be, yes.

And from what I have read, dynamic current consumption will be the the static (quiescent) current + the current drawn by the load during operation, right?
No, static current is the current drawn from the supply when its inputs and outputs are not changing. Dynamic current is the current drawn by the device when the inputs and/or outputs are changing, and is a function of frequency. Current drawn by the device when supplying current to a load (for example, to light an LED) is in addition to the device's static and dynamic currents.
 

Thread Starter

Electronic_Maniac

Joined Oct 26, 2017
253
Yes, pretty much; although I usually use the term "static current" when talking about CMOS logic devices, and "quiescent current" when discussing analog devices such as voltage regulators.


They can be, yes.


No, static current is the current drawn from the supply when its inputs and outputs are not changing. Dynamic current is the current drawn by the device when the inputs and/or outputs are changing, and is a function of frequency. Current drawn by the device when supplying current to a load (for example, to light an LED) is in addition to the device's static and dynamic currents.
Thank you
 

WBahn

Joined Mar 31, 2012
26,398
Thank you. I have been reading about these terms and I have a few doubts.

The static current consumption that you are talking, is also know as Quiescent current, right?
From what I have read, Quiescent current is the current which is used to turn the device on (to just power the internal circuitry of the device) and when no current is drawn by the load.
So, Quiescent current is also know as the static current which you are describing, am I right?
Are these terms used interchangeably?

And from what I have read, dynamic current consumption will be the the static (quiescent) current + the current drawn by the load during operation, right?

Thanks.
I think you are trying to mix concepts related to analog power amplifiers with those related to digital logic circuits. Need to be careful about getting too general.

Looking at the analog amplifiers, you are in the ballpark but it isn't as simple as you describe it. In general, an amplifier consumes quiescent when not driving a load, but to get the total consumption it is not as simply as just adding that to the current being drawn by the load for a couple of reasons. First, the power dissipated by the amplifier circuitry is not constant, so it changes as the load changes. Second, the two currents are not separate and some of the quiescent current gets diverted to the load. In some amplifier circuits the total current draw is nearly constant regardless of the load or the signal, all the changes is how much of that current is dissipated in the amplifier and how much is dissipated in the load.

For digital circuits, particularly larger circuits, the vast majority of the "load" seen by the various logic gates are the other logic gates in the same circuit. Also, the notion of "quiescent" isn't quite as simple. Does it mean just operating with no load? Or does it mean operating with no clock signal, too? That's why we use the word "static" -- we mean when nothing is changing, including the clock. But not all digital circuits can even operate under static conditions. Furthermore, many systems have a free-running clock driving the logic even if none of the inputs or outputs are changing and there are no external loads, but the digital logic still consumes power (and that power goes up as the clock frequency goes up, particularly for CMOS circuits).
 
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