TMP468: How to use TMP468 correctly?

HI Meican,

Below are my responses for your questions:

1. In TMP468 application , How can i select  a temperature sensor?  datasheet says MMBT3904LP .  this is a common NPN transistor ? 

In section 8.2.1 there is a list of parameters that we suggest looking for in selecting a remote sensors.  The recommend  MMBT3904LP transistor is commonly available from distributors. 

2.  if just use this type of NPN , how does it install  in a application ? for example,  a heatsink surface,  a speaker magnet surface,  a  chipset surface , a power mosfet surface,  just glue the transistor on the heat source?

Please  see this app note (http://www.ti.com/lit/an/snoaa29/snoaa29.pdf) for information on mounting locations and process. 

3.  if the connection cable is 3~3 m length ,  it need any compensation components before PIN D+ /D-?

This depends on the noise and resistance of the wire.  Please see section 7.3.2 of the datasheet on series resistance cancellation and 10.1 for layout guidelines.  If there is noise on the lines the series resistor and capacitor on the D+/- pins may need to be adjusted to filter out the noise.  See section 1.3 and 1.4 of this app note as well to see how to compensate for these errors. http://www.ti.com/lit/an/sboa173/sboa173.pdf

4.  How to select the tie point for  all 8 channel  D- , the D- connection point is located closed to pin D-  , or any else location ?

D- routing should be done as a differential pair as shown in Figure 18 in the above application note (http://www.ti.com/lit/an/sboa173/sboa173.pdf).  

Thanks,