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Some Problems about the Configuration Resistance and INTVCC of LTM4644

Question asked by Lvzp on May 15, 2018
Latest reply on May 18, 2018 by tkozono

Hi! There is trouble about LTM4644 on my own board.


1. The first one is about the configuration resistance. I set the output voltage as the guide on the datasheet. For example I set 1V output voltage with two parallel channels. The config resistance should be 45.45Kohm. I solder two 90.9Kohm with parallel connection between Pin FB and GND. But I test the resistance between the Pin FB and GND is 32Kohm after I solder them. The value of 90.9Kohm is ok before I solder them on  the board.

Then I test the resistance  between  PIN FB and PIN GND on a standalone LTM4644. The value is 214Kohm. It is not infinite. The 214Kohm is parallel connected with two 90.9Kohm resistance and the result is just about 32Kohm. The 214Kohm resistance between PIN FB and PIN GND will influence the configuration resistance. How do I deal with it ? Whether the guide on the datasheet is right? 


2. The INTVCC should be a 3.3V output. But the INTVCC on my board is below 0.5V.  The 5V input voltage is supplied on PIN VIN. Does the INTVCC 3.3V output is related to the voltage on the PIN RUN?