Do I need to limit current to IC's?

Sorry for what I can only guess is a very simple question.

Part of the system I am designing involves many IC's (Some flip flops, shift registers, buffers, etc.). My question is: If I have a system made up of these components, should I limit the current coming from the Arduino to those components with a resistor? I guess what I am asking is if there is any danger to my arduino if I take the 5v line right to the Vcc input of these IC's? Should I limit the current on purpose (if I can) so that the total current the arduino can output (I think I read somewhere 400ma total) can be used on the other pins where I actually run LED's and such?

Forgive me if this is such a basic question, I come from the world of software and just starting with hardware design.

Thanks!

FunkyJive: Sorry for what I can only guess is a very simple question.

Part of the system I am designing involves many IC's (Some flip flops, shift registers, buffers, etc.). My question is: If I have a system made up of these components, should I limit the current coming from the Arduino to those components with a resistor? I guess what I am asking is if there is any danger to my arduino if I take the 5v line right to the Vcc input of these IC's? Should I limit the current on purpose (if I can) so that the total current the arduino can output (I think I read somewhere 400ma total) can be used on the other pins where I actually run LED's and such?

Forgive me if this is such a basic question, I come from the world of software and just starting with hardware design.

Thanks!

No need, logic chips are designed to be voltage driven, no need to limit current to them. Just be sure the total current draw for all the external chips and other component don't exceed the current capacity of the 5V shield pin (which is the board's Vcc voltage) which is in the neighborhood of 400-700ma depending on if using USB or external power connector. If your external circuit requires more then that then one should use an external regulated +5vdc power supply, and wire the arduino ground to the external power supplies negative terminal. Arduino output pins are not really designed to power external chips as one should limit digital output pin current draw to 20-30ma max.

Lefty

Every device needs to get its rated power - if they are demanding more current that the supply can supply, you need to upgrade the power source, not try to starve devices of power.

If you just use CMOS logic chips power supply will not be an issue, note, since they take almost no power at all (unless switching at multi-MHz rates). So 74HCxx series will be just fine. If using older TTL chips (74xx and 74LSxx series) then you may find you have an issue with power - each chip takes a few milliamps constantly.

That sort of IC limits the current all by itself by having a resistance. You just supply the right voltage and make sure the power supply can supply enough amps if needed.

It's Ohms law: You set two of the variables in the equation and the third one sorts itself out (in this case the amps).

This is totally wrong

So 74HCxx series will be just fine. If using older TTL chips (74xx and 74LSxx series) then you may find you have an issue with power

Your backward here

74LSxxx means low power 74HCXXX are high power chips they can use way more power the a LS chip.

Let's take a 74LS164 it supply current is 27mA it's output per pin is 8 mA

Now take 74HC164 it's supply current is 50mA it's output per pin is 20 mA

be80be:
74LSxxx means low power 74HCXXX are high power chips they can use way more power the a LS chip.

Let’s take a 74LS164 it supply current is 27mA it’s output per pin is 8 mA

Now take 74HC164 it’s supply current is 50mA it’s output per pin is 20 mA

Do you think “HC” means High Current…?

Do I need to limit current to IC's?

The answer will depend.

It is never a good idea to overload any circuit. So in general, it makes sense to limit current to the load.

Having said that, unless you really have tons of such logic chips each loaded with their own heavy loads, you don't need to limit current: they consume very little current by themselves (in ua range).

If you really want to be safe, put something like a 10ohm resistor on the line: it also helps with decoupling.

dhenry:
It is never a good idea to overload any circuit. So in general, it makes sense to limit current to the load.

The only way to limit current to “IC’s (Some flip flops, shift registers, buffers, etc.)” is to reduce the voltage available to them. In which case they might stop working.

You only need to limit current where there’s a danger of using too much, ie. where the load’s resistance is variable. This simply isn’t the case here.

@ fungus

Do you think "HC" means High Current...?

This is 74HC D-Type Flip-Flop

Eight D-Type Flip-Flops in a Single Package  High-Current 3-State True Outputs Can Drive up to 15 LSTTL Loads

And the 74LS D-Type Flip-Flop uses half the current But to answer you HC and high current go hand in hand.

And @ FunkyJive you do not limit Current to these chips they will only use what they need Now if you had ask do you keep there output's from drawing to much Current then the answer would be Yes.

If the output pins are rated at 20mA as most 74HC chips are and the load is leds you would limit it to 20mA a led But if your switching a load that draws little or no power Like the data pins of a LCD then there's no need to limit anything.

be80be: This is totally wrong

So 74HCxx series will be just fine. If using older TTL chips (74xx and 74LSxx series) then you may find you have an issue with power

Your backward here

No it is you who are backwards HC stands for "High speed Cmos" they will take far less current than.

But to answer you HC and high current go hand in hand.

No they do not.

dhenry:

Do I need to limit current to IC's?

The answer will depend.

It is never a good idea to overload any circuit. So in general, it makes sense to limit current to the load.

Having said that, unless you really have tons of such logic chips each loaded with their own heavy loads, you don't need to limit current: they consume very little current by themselves (in ua range).

If you really want to be safe, put something like a 10ohm resistor on the line: it also helps with decoupling.

Also the total only to be expected absolute bollocks from dhenery - why do you bother if you know so little or are so inept at giving advice?

Grumpy_Mike:

dhenry: If you really want to be safe, put something like a 10ohm resistor on the line: it also helps with decoupling.

Also the total only to be expected absolute bollocks from dhenery - why do you bother if you know so little or are so inept at giving advice?

I thought the bit about the 10ohm resistor was particularly brilliant...!

I thought the bit about the 10ohm resistor was particularly brilliant...!

Well it is an old decoupling trick, that is the only bit that makes sense in his reply but not for the safety reasons he sited. It is like a poor man's inductor to add a little isolation.I would not recommend it though.

As was mentioned by all sensible contributors to this thread there is no need to limit current on the power lines or the signal lines when connecting an IC to an arduino.

Mike I no what HC stands for but Most all of the HC chips or as a fact all of the HC chips I’ve used use far more current then any of the LS chips

Take a 74HC164 and the 74LS164 shift registers

The 74HC164; 74HCT164 are high-speed Si-gate CMOS devices and are pin compatible
with Low power Schottky TTL (LSTTL). They are specified in compliance with JEDEC
standard no. 7A.

The 74HC164

Table 4. Limiting values
In accordance with the Absolute Maximum Rating System (IEC 60134). Voltages are referenced to GND (ground = 0 V).
Symbol Parameter Conditions Min Max Unit
VCC supply voltage ?0.5 +7 V
IIK input clamping current VI < ?0.5 V or VI > VCC + 0.5 V [1] - ?20 mA
IOK output clamping current VO < ?0.5 V or VO > VCC + 0.5 V [1] - ?20 mA
IO output current ?0.5 V < VO < VCC + 0.5 V - ?25 mA
ICC supply current - 50 mA
IGND ground current ?50 - mA
Tstg storage temperature ?65 +150 ?C

Now the 74LS164

over recommended operating free air temperature range (unless otherwise noted)
Note 3: All typicals are at VCC = 5V, TA = 25°C.
Note 4: Not more than one output should be shorted at a time, and the duration should not exceed one second.
Note 5: ICC is measured with all outputs OPEN, the SERIAL input grounded, the CLOCK input at 2.4V, and a momentary ground, then 4.5V, applied to the
CLEAR input.
Switching Characteristics
at VCC = 5V and TA = 25°C
Supply Voltage 7V
Input Voltage 7V
Operating Free Air Temperature Range 0°C to +70°C
Storage Temperature Range -65°C to +150°C
Symbol Parameter Min Nom Max Units
VCC Supply Voltage 4.75 5 5.25 V
VIH HIGH Level Input Voltage 2 V
VIL LOW Level Input Voltage 0.8 V
IOH HIGH Level Output Current -0.4 mA
IOL LOW Level Output Current 8 mA
fCLK Clock Frequency (Note 2) 0 25 MHz
tW Pulse Width Clock 20
ns
(Note 2) Clear 20
tSU Data Setup Time (Note 2) 17 ns
tH Data Hold Time (Note 2) 5 ns
tREL Clear Release Time (Note 2) 30 ns
TA Free Air Operating Temperature 0 70 °C
Symbol Parameter Conditions Min
Typ
(Note 3) Max Units
VI Input Clamp Voltage VCC = Min, II = -18 mA -1.5 V
VOH HIGH Level VCC = Min, IOH = Max
2.7 3.4 V
Output Voltage VIL = Max, VIH = Min
VOL LOW Level VCC = Min, IOL = Max
0.35 0.5
Output Voltage VIL = Max, VIH = Min V
IOL = 4 mA, VCC = Min 0.25 0.4
II Input Current @ Max Input Voltage VCC = Max, VI = 7V 0.1 mA
IIH HIGH Level Input Current VCC = Max, VI = 2.7V 20 mA
IIL LOW Level Input Current VCC = Max, VI = 0.4V -0.4 mA
IOS Short Circuit Output Current VCC = Max (Note 4) -20 -100 mA
ICC Supply Current VCC = Max (Note 5) 16 27 mA

You tell me which is backward The LS uses less power can output less power or is current not related to power?"

Grumpy_Mike: As was mentioned by all sensible contributors to this thread there is no need to limit current on the power lines or the signal lines when connecting an IC to an arduino.

Yep. The current is already bound by the laws of physics.

as a fact all of the HC chips I've used use far more current then any of the LS chips

You are talking about current ratings, vs. current consumption. HC (20ma typical) family can deliver much more current than the LS family (4-5ma typical)

Total current consumption depends on the load current + the chip's own idle current - hard to compare unless the same load is applied.

Both families consume very little current (the chips themselves, on the ua level), on the ua range. Drive current will depend on pin capacitance (comparable between the two families) and drive frequencies.

And maybe this was missed along the way SN74HC374 OCTAL EDGE-TRIGGERED D-TYPE FLIP-FLOPS WITH 3-STATE OUTPUTS

Eight D-Type Flip-Flops in a Single Package  High-Current 3-State True Outputs Can Drive up to 15 LSTTL Loads

The 74LS374 would go up in smoke trying to power what the 74HC374 can power

@ dhenry

Is not the OP trying to figure Power use and how to control it.

He needs a power supply that can handle use of all parts witch is not a easy slap a resistor on the VCC pin of the chips. I wouldn't limit current to any IC i would take into the fact what my uC needs and the supporting chips need and any loads.

Not really.

If the load is too tough, the output voltage would just deviate from the desired / target levels. You can simply think of the output stage as a perfect voltage source with a serial resistor. That serial resistor is higher for LS family than for HC family. So the highes wouldn't be quite high and the lows wouldn't be quite low.

Mike I no what HC stands for but

I assume that means you know what HC stands for.

I am not sure what the repeating of the specification is going to prove. In general HC logic has a lower power supply requirement than LS logic.

You are mixing up output current capacity with signal output current capacity.

See this paper:- www.fairchildsemi.com/an/AN/AN-319.pdf

I'm not mixing them The Op need to figure total power needs both input and output and design for this. A support chip be it a 74HC or 74LS is design to use only what it needs to switch states.

But that's not the big picture the ouputs are what's going to draw current

I'm sorry Mike I see what was being said about the HC chips I just don't see where that is related to OP asking if he needs to limit current to the chips. I'm sure he was thinking total use here not that a pin of the arduino could drive 20 or so inputs of a LS or 200 or more inputs of a HC chip

See this is what the OP ask

what I am asking is if there is any danger to my arduino if I take the 5v line right to the Vcc input of these IC's?

That's not the Input pin that's power to the chip and no resistor needed there chip draw only what it's made for now the load is where the problem begins.