Electronic – we buffer reset line

bufferreset

Today I saw the schematic of a lenovo G480-la-7981p (download or download). On page 6 you can see this part:

image1

In the green box you can see a buffered Reset line. My questions are:

  1. Why they've used a buffer? To filter noise?
  2. If so, then why a buffer? why not a simple capacitor?(e.g. 100nf) or an LC filter?
  3. What's the usage of resistors R32 and R34?
  4. I'm still diging whole of the schematic but don't get what is the difference between this resistor symbol 1 and this one 2 ?

Edit: datasheet of SN74LVC1G07DCKR

Best Answer

  1. It's actually used as a level-shifter. It's converting the 3V PCH_PLTRST# to a 1V open-drain signal. In many cases, the reset input of a CPU can also act as an open-drain output, so the CPU can reset the surrounding system. If that's the case, you shouldn't drive the reset pin using a push-pull signal, otherwise it will create a short circuit when the buffer drives high and the processor pulls low.
  2. -
  3. R32 is the pull-up, see above. Not sure about the purpose of R34 though.
  4. The special resistor symbol stands for a bridge made by solder or directly on copper on the PCB, but still offers the possibility to remove the bridge and install a component. The @ near means, that no component is installed.
Related Topic