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.
The document explains two possible startup behaviors for STMicroelectronics L9903 and L9904 devices depending on the voltage over Cpgg during initial power-up. If the voltage exceeds 3.5V, the device behaves as shown in Figure 1; otherwise, it may enter a state where the high-side driver gate switches to CBx (Figure 2), potentially causing increased leakage current or incorrect diagnosis in standby mode applications.
The device switches to a specific behavior when the voltage over Cpgg exceeds 3.5V.
The supply voltage (Vs) must be greater than 7V before the EN pin is set high.
The EN pin must be high for more than 50 microseconds before a signal change is detected.