7.4.1 Power-Up Sequence

The basic application circuit is shown in Figure 20 and a normal start-up sequence is shown in Figure 21. Start-up of the LM5060 is initiated when the EN pin is above the (EN_THH) threshold (2.0 V). At start-up, the timer capacitor is charged with a 6-µA (typical) current source while the gate of the external N-channel MOSFET is charged through the GATE pin by a 24-µA (typical) current source.

When the gate-to-source voltage (V_GS) reaches the V_GATE-TH threshold (typically 5 V) the V_GS sequence ends, the timer capacitor is quickly discharged to 0.3 V, and the 5-µA current source is enabled.

The timer capacitor will charge until either the V_DS Comparator indicates that the drain-to-source voltage (V_DS) has been reduced to a nominal value (i.e. no fault) or the voltage on the timer capacitor has reached the V_TMRH threshold (i.e. fault). The V_DS Comparator monitors the voltage difference between the SENSE pin and the OUT pin. The SENSE pin voltage is user programmed to be lower than the input supply voltage by selecting a suitable sense resistor value. When the OUT pin voltage exceeds the voltage at the SENSE pin, the nPGD pin is asserted low (i.e. no fault) and the timer capacitor is discharged.

Figure 20. Basic Application Circuit