slyt096Power Management Texas Instruments Incorporated Soft-start circuits for LDO linear regulators By Jeff Falin (Email: j-falin1@ti.com) Applications, Portable Power Many low-dropout (LDO) linear regulators do not have an integrated “soft-start” function that limits the in-rush current to the device being powered. In fact, as the simplified block diagram in Figure 1 shows, most linear regulators consist of only a reference, an error amplifier, and a pass element. Thus, at startup, the error amplifier senses that the output voltage is low and drives the pass element as hard as possible. The pass element pulls a large in-rush current to charge the output capacitance and/or load current abruptly, after a short delay. The delay is caused by three factors: the time required for the input voltage ……