Question on how to measure temperature using TEMP pin on LTM4648

Question

hello? 
 I have two questions as below. 1) If you look at the Temperature Monitoring paragraph in the LTM4648 datasheet, you will find the following formula and graph. But I don't know what value to calculate ID and IS. Please let me know how to calculate the temperature through Vd (TEMP pin voltage).

2) Figure 7 shows Id=100uA. Is there a relationship between Id=100uA in Figure 7 and DC1856A's RS value of 10K and 1% resistance? 
 
 Thank you for your support.

ADIApproved · Accepted Answer

Hi Justin, sorry for the confusion. 
 1) If you are using 100uA current source, you can refer to figure 7 to read the temperature. If you are using another current source, you can do the calculation as below. Per the datasheet page 17, the equation VD = T(KELVIN) x KD x In(ID/IS). The ID diode current is generated externally, so ID is per your design. The IS saturation current is a process dependent parameter, which is hard to calculate, but it can be eliminated by measuring the diode voltage at two different current source, and take the minus. As described in the paragraphs in page 17, you can use 10:1 ratio current sources (ID1 = 10 x ID2), and measure the diode voltage at the same temperature. Thus delta_VD = T(KELVIN) x KD x In(10) = T(KELVIN) x 198uV/K. Thus by measuring the delta_VD, you will know the T(KELVIN). 
 2) The demo board is not designed at 100uA. The internal PNP transistor is MMBT3906. Use VBE = 0.7V, the diode current can be calculated as (VIN-0.7V)/10kohm. 
 Regards, 
 Susan)

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Question on how to measure temperature using TEMP pin on LTM4648