ST AN2229 APPLICATION NOTE

AN2229

APPLICATION NOTE

Startup Behavior L9903/L9904

Introduction

Purpose of the Application Note is to detail the startup behaviour 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.

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AN2229

Contents

1 Explanation of 2 possible Startup Behaviors . . . . . . . . . . . . . . . . . . . . . . . 3

2 Application example using standby voltage monitoring . . . . . . . . . . . . . . 4

3 Proposed initialization sequences for L9903: . . . . . . . . . . . . . . . . . . . . . . . 5

4 Proposed initialization sequences L9904: . . . . . . . . . . . . . . . . . . . . . . . . . 6

5 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

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AN2229

1 Explanation of 2 possible Startup Behaviors

1 Explanation of 2 possible Startup Behaviors

Starting condition: the device is disconnected from the battery.

After switching on VS, as long as the voltage over CBoot is below 3.5V, the device can have 2 startup states:

a)Gate of high side driver is internally switched to ground (Fig. 1).

b)Gate of high side driver is internally switched to CBx (Fig. 2).

If the voltage (CBoot) exceeds 3.5V the device switches always like shown in figure 1

Figure 1. Startup behavior internal switched	Figure 2. Startup behavior internal switch to
to ground (state 1)	CBx (state 2.

After the first VS ramp up the outputs will enter one of the explained states.

If the device enters state 2 and the threshold of the external MOSFET is below 3.5V, the Sx pin will raise and the charging of the bootstrap capacitor will be stopped. This state will persist until the L9903/04 will be enabled by the EN pin. The only consequence of entering state 2 is an increased leakage current. There is no influence on the standard application suggested inside datasheet. There is no influence on operating condition (EN=HIGH). If the application requires a startup behavior like in figure 1, an initialization is needed (see sections 3 and 4).

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