ADL5513 temperature compensation with a single resistor

Hi Turker, this is an older part so it's difficult to get information on it. I don't think that it's a good idea to rely on the internal resistances on the TADJ pin. You are proposing to make a resistor divider using the resistor that is tied to Vinternal combined with the internal resistor to ground in parallel with a single external resistor from Tadj to ground. My problem with this is that the internal resistances will change from part to part and over time with the semiconductor process (typical guidance is that these resistances can vary by +/-10 to +/-20 %. 

If I can get my hands on an evaluation board, I could measure the resistance from Tadj to ground. If I then measue the Tadj voltage, the resistor from from Tadj to Vinternal can be back calculated. If you have an evaluation board, you could probably get this measurement done quicker than I can. I would then recommend setting the external Tadj resistors to be an order of magnitude lower than the internal values. This will reduce the sensitivity of  the Tadj  voltage setting to the variances in the internal resistors. - Eamon 

Hello again Turker,

I managed to get my hands on an ADL5513 evaluation board. The resistance from TADJ to ground measured at 15.383 Kohms. I then powered up the board and measured the voltage on the Tadj pin with no components attached. That voltage came out at 0.8998 V. I cannot measure the resistance from Tadj to “Vinternal” because the Vinternal node is not accessible (I measured the resistance from Tadj to the supply and that came in at 649kohms so that is not relevant). My guess is that Vinternal is around 1.9V. that work make the resistance from Tadj to Vinternal also equal to around 15.3K.  Based on this, I don't think that it's a good idea to try and set the Tadj voltage using an external resistor. Because the Tadj voltage is already very close to 0.9V, you would need to connect a very large external resistor to move it to its target value which ranges from 0.8V to 0.9V (Table 4). So I think that its better to use a resistor divider between supply and ground whose total resistance is  around no more than around 3K (i.e. an order of magnitude smaller than the internal resistances). 

Please let me know if this answers your question and if there are any more issues you need assistance with. 

Best Regards

Eamon