Arduino Forum

Using Arduino => General Electronics => Topic started by: arduidiot on Oct 03, 2014, 08:17 pm

Title: the I in a circle in IC schematics / block diagrams
Post by: arduidiot on Oct 03, 2014, 08:17 pm
its a multimeter set to measurement in amps yes? but can also be read as the analog input of another chip yes?

see below

also is it the quiescent current drawn by the circuit thats supplying Vdd to the IC or the quiescent current of just the IC in standby mode itself? If its the amount drawn by the circuit its connected to then i can see obvious battery life monitor implications but yea i guess i dont have my bearings again
Title: Re: the I in a circle in IC schematics / block diagrams
Post by: MarkT on Oct 03, 2014, 08:27 pm
Its to show what measurement was made.

quiescent means "at rest", ie no signals coming in, no loads on the outputs.

The CD4xxx series have extremely low quiescent current draw as they are CMOS.
Title: Re: the I in a circle in IC schematics / block diagrams
Post by: arduidiot on Oct 03, 2014, 10:37 pm
yea, so when they say its the quiescent current of the device it means that the indicated circuit schematics can be used to measure the quiescent current of the "device" as a whole, being able to approximate the contribution to its measurement provided by the the stand-by mode of the CMOS IC itsself to zero,allowing the measured value to be considered be the draw of the total circuit?
Title: Re: the I in a circle in IC schematics / block diagrams
Post by: MarkT on Oct 03, 2014, 11:23 pm
Who said anything about a standby mode?  Its the quiescent current draw, the current
drawn when outputs are unloaded and inputs are not changing.  We are talking
CD4000 series logic chips...
Title: Re: the I in a circle in IC schematics / block diagrams
Post by: TomGeorge on Oct 04, 2014, 03:16 am
Hi, that diagram shows you how the manufacturer set the IC up to measure the quiescent current that is quoted in the specs for a 0 and then for 1 on the inputs.
This current is the current supplied by the Vdd.

This sort of spec is only relevant if your are using hundreds of them in a circuit, even then its probably insignificant.
Or if you had only micro-amps of supply current to use.

Do not over think this, in most / 99.999% of cases this is insignificant.

By the way you answered your own question in your first post, the I in the circle represents a meter.

Tom... :)

Title: Re: the I in a circle in IC schematics / block diagrams
Post by: arduidiot on Oct 04, 2014, 03:57 am
No its just that i read SOMEWHERE i honestly cant remember where so cred is well same as everything really that measurement of this current value is a very important analog input for approximating battery life because im trying to work out the optimization problem you face with recharging li ion batteries on a 24 hour schedule with a solar panel so yea obv i want to maximize their efficiency in that the recharge mode frequency in time is minimized allowing the source - determined effective battery life being i guess the most "sketch loops" ran in time is maximized
Title: Re: the I in a circle in IC schematics / block diagrams
Post by: JimboZA on Oct 04, 2014, 06:05 am
arduidiot, could you please do us all a favour and use some sentence punctuation?

Paragraphs like this....


No its just that i read SOMEWHERE i honestly cant remember where so cred is well same as everything really that measurement of this current value is a very important analog input for approximating battery life because im trying to work out the optimization problem you face with recharging li ion batteries on a 24 hour schedule with a solar panel so yea obv i want to maximize their efficiency in that the recharge mode frequency in time is minimized allowing the source - determined effective battery life being i guess the most "sketch loops" ran in time is maximized


.... are really difficult to read.

Title: Re: the I in a circle in IC schematics / block diagrams
Post by: Paul__B on Oct 04, 2014, 07:14 am

I read ... that measurement of this current value is a very important analog input for approximating battery life.

It is.

So the "take home message" for you is that this current is so low that you need not worry about it in your calculations with one caveat - that as in those test diagrams, all inputs are tied either to a LOW or HIGH value, which they would be if each is either controlled by a pull-up resistor or (but not both) driven by the output of another CMOS device.

A CMOS device in which no switching is occurring (no clocks running) is effectively in "standby" as far as you need to be concerned.  What you need to be worried about is devices requiring current, such as indicators, or resistor networks which span from one supply terminal to the other or have a voltage applied when a chip output is in a certain state, or a switch in a certain position.

Title: Re: the I in a circle in IC schematics / block diagrams
Post by: Grumpy_Mike on Oct 04, 2014, 07:25 am
Quote
I read ... that measurement of this current value is a very important analog input for approximating battery life.

You never read that. You read something that you misunderstood to be that.

The quessent current is irrelevant to you you need to know the real current in your real circuit.
Title: Re: the I in a circle in IC schematics / block diagrams
Post by: arduidiot on Oct 06, 2014, 07:25 am
ok thanks ill just read until i get it