Tracking of LM3495

The 0.65 V is to ensure that the final voltage at the TRACK pin is higher than the internal reference voltage of 0.6 V. This will allow the converter to regulate to the voltage set by the feed back resistor divider. If the TRAcK pin is below 0.6 V, then the output voltage will be lower than expected as the reference to the error amplifier will be the lower of TRACK and VREF.

I do not see any reference to Vss. Do you just mean the tracking voltage as above?

Takahiro-san,

There are 2 basic reasons why Tracking function is used.

1) For the master power supply to reach its set output at the same time as the LM3495. In this case irrespective of the master power supply output voltage, LM3495 reaches its set output at same time as the master.  (Page 14, eq1)

2) For the slew rate of the master power supply and LM3495 to be similar. This means the rate of rise dv/dt of the master and LM3495 output would be similar but does not mean they reach the set points at the same time.  (Page 14, eq2)

0.65V in the eq1 is set to be 50mV higher than 0.6V (the reg voltage of the LM3495). The TRACK pin acts as REF whenever it is below 0.6V, once it exceeds 0.6V then the REF is the master. The accuracy of the 0.65V is determined by the resistor divider tolerance from the master power supply.

If your question is to make sure what tolerance range 0.65V should be set at, I would recommend 50mV higher than the highest Vref value over temp. That is 0.609V in the datasheet.  So the recommended value would be 50mV + -.609V= 0.659V.

Then you should consider the lowest Voltage tolerance of the master and set the resistor divider such that at the worst case low voltage of the master the TRACK pin is at 0.659V. In normal operation you want the TRACK pin volatge to be always higher than the VREF.

Regards,

Mathew