74ls00 Power consumption?

[yviswanathbe]

Hi,

I need to calculate power consumed by the 74ls00 IC in my circuit.

In the datasheet of 74ls00 quadruple 2 input positive NAND gate ICCL and ICCH parameters are mentioned.
Does these parameters are for whole IC or individual Gates?

Some body please help me in this regard.

Thanks and Regards,
Viswanath

 

[betwixt]

The figure quoted is probably for a static logic condition. The power consumption depends on several factors, the most prominent being how fast the logic state is changing. If you look in the data sheet you should find a calculation that tells you current consumption vs. frequency. You know what the power supply voltage is so multiply V x I to find the power consumption.

Brian.

 

[yviswanathbe]

Hi betwixt,

Thanks for your reply.
In the datasheet i did not find the plots.
I have attached the schematic, can you tell how can i calculate the power consumed by the IC's?

I have calculated for U2 as follows:
output current=1.35mA (input of ULN2803 is 1.35mA max)
Supply Current Icc=4.4mA ( I have considered page no.5 of 74ls00 datasheet)
Supply Voltage=5V
Power= 5*4.4mA=22mW. (here i have confused...there are four gates.Should i multiply the result with 4 or this is power consumed by the IC)

Is this calculation Correct?

Looking forward for the positive response.

Thanks and Regards,
viswanath

 

[betwixt]

To be honest I'm not absolutlely certain but the data sheet gives two ICC currents, one for each logic state so I would imagine it refers to each gate.
There are only four gates in the package so the calculation would be 4*4.4mA = 17.6mW assuming the 4th gate is also used. Add to this the input current of the ULN2803 to get the total.

With 74LS series devices, the current remains fairly constant up to a certain frequency then it starts to increase. As you are driving relays, the frequency is presumably very low so the extra speed factor can be ignored. There is more about this at: www.fairchildsemi.com/an/AN/AN-319.pdf

May I ask what is th purpose of the input IC? With the latch and enable tied as they are, it only works as a buffer, you could probably remove it to save power and directly drive the LS00.

Brian.