The device can have V_IN, V_BIAS, and V_EN sequenced in any order without causing damage to the device. However, for the soft-start function to work as intended, certain sequencing rules must be applied. Enabling the device after V_IN and V_BIAS are present is preferred, and can be accomplished using a digital output from a processor or supply supervisor. An analog signal from an external RC circuit, as shown in Figure 7-3, can also be used as long as the delay time is long enough for V_IN and V_BIAS to be present.

Figure 7-3 Soft-Start Delay Using an RC Circuit on Enable

If a signal is not available to enable the device after IN and BIAS, simply connecting EN to IN is acceptable for most applications as long as V_IN is greater than 1.1 V and the ramp rate of V_IN and V_BIAS is faster the set soft-start ramp rate. If the ramp rate of the input sources is slower than the set soft-start time, the output tracks the slower supply minus the dropout voltage until the set output voltage is reached. If EN is connected to BIAS, the device does soft-start as programmed provided that V_IN is present before V_BIAS. If V_BIAS and V_EN are present before V_IN is applied and the set soft-start time has expired then V_OUT tracks V_IN.