The UCC28630 overload timer trip level and time constant are both selectable from a defined list of combinations. The user can select the overload timer trip level as a percentage of the rated continuous nominal power, PNOM (see Figure 41), and the timer response speed. The available choices are detailed in Table 1.
|RPROG PROGRAMMING RESISTOR (kΩ)|
(E96 series values)
|TIMER CONTINUOUS OPERATION PTRIP/PNOM (%)||TIME CONSTANT AT 200% of PNOM OR IN CC MODE (ms)|
|Open, or > 47||160||1000|
The desired pull-down resistance on the DRV pin sets the required overload parameters, as shown in Figure 36. The controller measures the resistance value on the DRV pin at start-up using a low-level test voltage (400 mV to ensure it is well below the lowest possible power MOSFET gate threshold voltage) and sensing the current that flows. Thus, based on the resistance RPROG, the required set of timer parameters can be chosen.
To ensure that the sensed current does not sit close to an interval boundary, the resistor values listed in Table 1 (or the closest value possible) should be used. These recommended resistor values position the test current in the center of each interval.