Current consumption for logic chips

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Hi,

 

I am looking to make a logic chip tester.  There are a ton of variety of logic chips out there, as I understand.  The two questions I have are, because the VCC and GND pins of logic chips can vary, not always the last pin (GND) on the left side of a chip and the 1st pin (VCC) of the right side of a chip.

 

1) I want to be able to find out the minimum input/drawn current or a chip.  Looking at the datasheet for the HC595[1], for example, I see Iik (input clamp current) is +/- 20mA.  Is that 20mA the max current consumption for this chip? I could be smart and test this chip with individual output turned on, thus consuming around 10mA each test or turn on all 8 outputs, thus consuming 80mA!  Could I use even an ATMEGA's I/O pins to source the VCC pin of this chip or to ground the GND pin of this chip with a zero output?  Of course, I do realize that I cannot source 80mA out of an ATMEGA's GPIO pin.  That brings to the 2nd question below.

 

2) If there is a chip I can use to be able to provide a chip's GND or VCC, that would be good to use.  And this "magic" chip could source more current?  Transistors?  MOSFETs, etc.?  Given a pin of the chip to be tested, I want to be able to interface to that chip's pin either as an input/output or GND or VCC pin.

 

Thanks.

 

 

 

[1] https://www.ti.com/lit/ds/symlin...

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Your the answer to your question depends strongly on the logic family. CMOS tends to draw "almost" no power unless the inputs change a lot OR the output drives some current consuming load (example LED). CMOS, practically takes no input current unless it is toggling because inputs look like capacitors. Outputs take very little current unless togging, then the effective power supply current is approximately proportional to frequency (plus, of course, static or dynamic load currents).

 

Clamp current comes from external circuitry, especially inductances. That has NO bearing on the normal current draw of the device.

 

Methinks you would be well served to do a bit of background study about the design details of modern logic.

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

Last Edited: Mon. Mar 8, 2021 - 02:30 AM
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 Is that 20mA the max current consumption for this chip? 

Um... if you are asking such a question, it is doubtful you will be building a logic chip tester, until you get a lot more details & understanding of the basics.   There are some such project out there already---your best bet may be to build & modify one of those.  Have you worked much with logic chips?  Is your tester going to try to identify which type of chip you plugged in (there are projects for that as well).  

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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Hint -

 

The current used by CMOS logic, except for very, very, low data "toggle" rates, (itself, that is, not accounting for loads) depends almost entirely on the toggle frequency.

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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Non-CMOS logic chips can have supply current up to about 200mA.

(190mA listed for a TI 74S374...)

 

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Hai

 

westfw wrote:
Non-CMOS logic chips can have supply current up to about 200mA.

 

40/HC/HCT were CMOS

 

Did you PS current low ? I got similiar situation with USB powered kit which also drive the CPC1966s https://www.mouser.com/IXYS/Elec...

 

Regards

JSB

 

 

www.tokopedia.com/madagang .Buy and Donated cheap electronics and manuscripts.

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There is heaps of information available on the internet around TTL/CMOS logic. I have been researching a lot lately for a circuit I am designing. I think this may help with the current consumption figures a little -

 

Quote:
When a LS TTL gate output acts as a source, a maximum source current of -400µA is available to be drawn from the output terminal. Note that the minus sign used in this case signifies a current that is flowing FROM the gate output. When the output is sinking current, the LS TTL gate is able to sink 8mA. Notice the sink current has no minus sign as it flows into the output terminal.

 

https://learnabout-electronics.org/Digital/dig33.php

Wayne

East London
South Africa

 

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That's got very little to do with current consumption. What you quoted is the output drive specs. To pull a TTL input low requires some current, so you need to consider fan in/fan out when designing.  This is rarely an issue when using CMOS - capacitance tends to be the deciding factor.

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I wonder is this just for learning and fun, or do you have some other goal?

Current can be 0 to 200mA, depending on how you test and what you want to test. (clocks running or not, inputs & outputs changing level,load applied to the output pins, supply voltage)

Keep in mind that normally the chips you get will be factory tested and thus are within the set specified limits.

 

 

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Current consumption is VERY different for CMOS and TTL and even more different for ECL. The effect of clock rate is wildly different among these three types. The nature of the load has a very big effect; CMOS (mostly) can equally sink or source current. TTL can sink but sources quite weekly. ECL is, for the most part, designed only to work with other ECL devices as loads. 

 

CMOS internal current consumption depends strongly on clock or data switching rate. TTL depends only lightly on clock or data rate. ECL depends very little on clock or data rate. 

 

The OP needs to learn more about logic types before heading down the proposed road!

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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I fail to see how knowing the current consumption of a chip will allow the OP to work out which pin is VCC and which is GND (or VDD and VSS if you prefer)?

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

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I'd tell the OP to just pick another project, or look at one that has been done.

 

Does it need to test QFN parts?

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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In reference to the old thread that was awakened, even on 14 pin dip TTL, power is not necessarily on pins 7 and 14! Off the top of my head - 7490 and 7475 had power elsewhere. These tend to be more the exception though.

I have an ic tester and programmer - a HiLo ALL-07. I don’t think I’ve ever used the ic test feature in over 25 years. I still use it to program and read eproms, pld and flash chips.

It has a ton of transistors, ics etc to create near on fully programmable pins. There’s a bit of info and schematics on the web for it and the later model all-11.

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Kartman wrote:
HiLo

That came out of Brunel University: https://community.cadence.com/ca...

 

I remember  Gerry Musgrave

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If only those chips would come with datasheets! indecision

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

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