When the operating mode of the load-side IC is changed, the output voltage of an LDO regulator drops, causing the IC to malfunction. What can I do to prevent a malfunction?

In the event that the supply current changes sharply because of a change in the operating mode of the load IC, the output voltage of the LDO regulator drops instantaneously. In this situation, the LDO regulator provides negative feedback to return VOUT to a normal level. However, an LDO regulator with slow response exhibits a long foldback recovery time. The load-side IC might malfunction if its input voltage drops below the lower limit.

The use of an LDO regulator with excellent load transient response helps reduce a drop in VOUT and recovery time and therefore prevent the IC malfunction.

The drop in VOUT can also be reduced by increasing the value of the output capacitor. In this case, however, care should be exercised as to the rise time, oscillation, and inrush current immediately after the turn-on of the LDO regulator.

Figure 1 LDO regulator with fast load transient response
Figure 1 LDO regulator with fast load transient response
Figure 2 LDO regulator with slow load transient response
Figure 2 LDO regulator with slow load transient response
Figure 3 Example of load transient response characteristics with different output capacitor values
Figure 3 Example of load transient response characteristics with different output capacitor values

For LDO’s load transient response, please refer to

For LDO regulators with fast load transient response, click:　

For other LDO regulators, visit the main web page of LDO regulators at:

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