The purpose of this application note is to detail the startup behavior of L9903 and L9904 devices and to explain a correct initialization sequence, possibly being necessary when application configuration is different from the one suggested inside datasheet. In fact, in case an additional, external diagnostic structure is used, it may happen that after a first connection of the supply voltage, and before first enabling of the device, the measurement results of these diagnostic structure is not precise. This note also provides an application example using standby voltage monitoring.