Don't defeat the UVLO in the 3842 (by Gerard Larooy)

Component: 3842

Category: Power processing IC's

This is the most popular part number of a series of current mode SMPS chips designed for driving a single low side MOSFET. The IC has an internal UVLO with some hysteresis which prevents the MOSFET going into analogue mode and burning out. The UVLO turn on voltage can be as high as 16V on the most common 3842/4. There are other variants with lower thresholds which would be Ok for a 12V system but they are less common and for some applications won't go low enough. An article was written on how to defeat the UVLO by forcing 5V on pin 8, the reference pin, which according to the Unitrode block diagram should work. Beware - this didn't work when I tried it. It could be said that the author of the article had a chip from a different manufacturer when he tested his circuit. In summary it's best not to defeat the internal UVLO and live with the existing thresholds.

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