My ICs are getting hot :(

[Edo Reshef]

Hey Everyone,
I got a heat problem with some circuit I made and I hope you can help.

First let me give a short description of the circuit:
Encoder input is decoded using LS7084 (Encoder to Counter Interface
Chip), The Up/Down and Clock outputs are connected to three 74F269 (8
bit bi-directional counters) and the outputs of the counters are
connected to 74HC573 latch.

The problem is that the three counters are getting quite hot (I
actually measured 46 degrees Celsius). I have checked the 74F269
datasheet and found it uses 100mA Supply current, witch sounds it me
like a lot. it means that each IC takes about 0.5W.

The things I'm trying to understand are:
Could 0.5W make so much heat?
Are those ICs suppose to get so hot? And if not, what could cause
that?
Why the poor 74F269 wants so much current?
Could the cause be that the 74F269 are a TTL and the 74HC573 are CMOS?

Best regards,
Edo Reshef

 

[Ban]

Edo Reshef wrote:

Hey Everyone,
I got a heat problem with some circuit I made and I hope you can help.

First let me give a short description of the circuit:
Encoder input is decoded using LS7084 (Encoder to Counter Interface
Chip), The Up/Down and Clock outputs are connected to three 74F269 (8
bit bi-directional counters) and the outputs of the counters are
connected to 74HC573 latch.

The problem is that the three counters are getting quite hot (I
actually measured 46 degrees Celsius). I have checked the 74F269
datasheet and found it uses 100mA Supply current, witch sounds it me
like a lot. it means that each IC takes about 0.5W.

The things I'm trying to understand are:
Could 0.5W make so much heat?
Are those ICs suppose to get so hot? And if not, what could cause
that?
Why the poor 74F269 wants so much current?
Could the cause be that the 74F269 are a TTL and the 74HC573 are CMOS?

Edo, you are right, the older F parts use a lot of current and get hot. Your
counter has 113mA consumption, but the 74F579 has only 75mA, tho it is in
another package. You could also use 2 cascaded 4bit counters in another
technology (AC or ACT) which would draw much less current if you do not need
100MHz switching speed.

--
ciao Ban
Bordighera, Italy