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DC-DC Conversion Cookbook Slide 21

A common issue with low quiescent current LDOs like the STLQ015 is the load transient response. When the system wakes up, the step change of the load current from 1 µA to around 10 mA will cause an undershoot in the output voltage, due to the response time of the feedback loop. The lower the quiescent current, the slower the error amplifier will be. This affects the feedback loop response time and the direct consequence is a noticeable negative spike that may even cause the reset of the µC or other sensitive circuitry powered by the LDO. The trade off is between a low quiescent current and a fast transient response performance. The plot shows the STLQ015 load transient response to a typical step change in load, about 100 mV and shows how the LDO has a fast load transient despite the low quiescent current. This is a key advantage of the STLQ015, sometimes overlooked by customers when the focus is primarily on minimizing the Iq. The plot on this slide also shows the static load regulation, due to the finite gain of the error amplifier.

PTM Published on: 2013-04-11