This design is for???

[johansenng]

Hi, sorry but i am new in this. This is a Freescale SRB ZigBee node schematic design.

1)Can anyone help me identify what is the use of the 10K ohm resistor (R115) used? Seems that there is some advantages and disadvantages of using it.
The source is a connector from USB_power and feed to 2 diodes before going to a voltage regulator.

**broken link removed**

2)Why is two capacitor (C116 & C117) used in this case instead of one? Is this an 'extra safe' design?

**broken link removed**

Where can i find more information about such designing tips used?

Thanks!

 

[ze_dib]

Hi,

R115 fonction is to tie the connector pin to 0V when unconnected.

The two capacitors are in parallel, each as a frequency siltering effect on the ripple, related to it's value and it's material. Usually, there is a big capacitor (about µF) in // with a tiny one (many pF) in order to filter High frequency ripple with the tiny, and to face the load variation with the big one.

Hope It help.

Regards,

Ze_DiB

 

[Kral]

johansenng,
1) My guess is that it's for static protection. Usually a capacitor in parallel with the resistor is used.
.
2) There are two schools of thought on this. The first school says that by using two different widely space values of capacitor, you swamp out the resonant effects of the larger capacitor by putting the smaller capacitor in parallel. The idea is that at the resonant frequency of the larger capacitor, the smaller capacitor will be purely capacitive.
.
The second school of thought is that you do more harm than good by using this technique because now you have two resonant peaks. Search for the Cypress application note AN1032 "Using Decoupling Capacitors" for more details.
Regards,
Kral