UCC28610: UCC28610 MOT pin

Hello John,

It appears that the block diagram is not very clear on this function, and I believe that the comparator function on MOT is not strictly drawn as to its function.

However, I interpret it to mean that that comparator detects whether the MOT voltage is either above 3V or below 3V and adjusts the Fault response as Latch-Off or Retry respectively, per Figure 19 of the datasheet (page 15). There must be a current coming out of the MOT pin that sets up a voltage (Vmot) across the MOT resistor to GND.  For Rmot below 120kR, the Vmot < 3V and for Rmot > 120kR, the Vmot > 3V. 

Simple math suggests that the current is 3V/120kR = 25uA.  I believe that Vmot also generates a separate timing current (not shown) that sets the maximum on-time.  The comparator also changes the gain of an internal current mirror by a factor of 5 to generate the same timing current from the higher resistance range as it does with the lower resistance range.  You can see that a 30k-to-100k range has the same timing range as the 150K-to-500K range. This way a single pin performs 2 programming functions: determining maximum on-time and selecting retry vs. latch-off fault response.

The block diagram is overly simplified, I believe.

Regards,

Ulrich