Why no short?

Community Projects
1

Hello,

I am using a CD74HC243 quad bus transceiver chip. In the input of a buffer, I applied a 3.3Vdc while keeping its respective output grounded.

I was just curious as to why the chip is able to handle this without burning up. When the 3.3VDC passes from B0 to A0, doesn’t this make a short??

Please view the following attachment of my circuit!

Thanks to all in advance for your feedback.

2

http://en.wikipedia.org/wiki/Fan-out

Generally, a chip’s output can only drive so much current. Put an ammeter on that pin and you’ll likely see only a handful of mA. Page 3 of the datasheet, under maximum ratings.

3

okay, that makes sense!

thanks for your help skimask!

4

Problem with most datasheets is that you generally only see a block diagram of what’s going on.

Most of the time, especially with more complicated chips, you won’t get to see exactly everything inside the chip (eg. MOSFETs, pull ups, pull downs, diodes, etc.).