i want to understand the thought process and ideas behind these:

see the schematic

http://www.pololu.com/catalog/product/2124

1 - what is the n-FET and diode (Q1 and Q2) component means?

2 - why the 4.7kOhm resistors used instead of 10kOhm like in the datasheet here (also applicable to other circuit,this is just an example to help me understand) http://www.pololu.com/file/download/LSM303DLHC.pdf?file_id=0J564

3 - how designers verify that the component values used will yield the desired result? i mean they are only provided with IC and its datasheet,sure they need to do simulations to verify the circuit. do they model the IC?How's the simulation done for e.g?

4 - any tut/books to help me understand better how to connect IC with external components?like from a pin of an IC with sensor/op-amp,choose values,what to consider, how to verify etc. or IC pin as a driver.

thx

 

Hi reuken. Welcome to the forums.

1 - The LSM303DLHC runs off 3.3V, and lots of other devices use 5V. Q1 and Q2 form a level shifter to "translate" from one set of logic levels to the other. (I only know this after reading last week a Phillips app note describing this technique)

2 - The pull up resistor value isn't etched in stone. Lower values can run at higher speeds. I can't comment on the link you put as I'm not reading a 42 page doc to find what you saw. <grin>

3 - Believe it or not, some of use actually BUILD things, then measure what happens.

4 - The LSM303DLHC used the I2C interface, which is a two wire clock and serial data method of bidirectional communication. You can find lots of references on the web (Wikipedia has a good one). There's also a link on the sales page to a Phillips page.

As far as the LSM303DLHC device itself... I got nuthin. Never used one.

 

thx ErnieM

for 2nd Q: it is stated to use 10kOhm in section 4 of datasheet but you already provide the explanation.