AN2229 APPLICATION NOTE
Star tup 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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Contents
1 2 3 4 5 Explanation of 2 possible Startup Behaviors . . . . . . . . . . . . . . . . . . . . . . . 3 Application example using standby voltage monitoring . . . . . . . . . . . . . . 4 Proposed initialization sequences for L9903: . . . . . . . . . . . . . . . . . . . . . . . 5 Proposed initialization sequences L9904: . . . . . . . . . . . . . . . . . . . . . . . . . 6 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
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1 Explanation of 2 possible Startup Behaviors
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Explanation of 2 possible Startup Behaviors
Star ting 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) b) Gate of high side driver is internally switched to ground (Fig. 1). 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 to ground (state 1)
Figure 2.
Startup behavior internal switch to 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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2 Application example using standby voltage monitoring
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Application example using standby voltage monitoring
Figure 3. DC motor driving with additional diagnostic (RD1, RD2, RD3)
Vcc RD1 ADC
GH 2 S2
L9903/04
GH 1
M
GL1 S1 GL 2
RD2
RD3
Some applications may use external circuitry, for instance for advanced diagnosis in standby mode. In figure 3 for example, an additional external resistive network is implemented, to measure a potential short circuit or open load condition. A short circuit or an open load condition can be detected by the ADC of a microcontroller, by monitoring voltage levels of the resistive network. If L9903/04 is not initialized correctly upon first VS ramp up, the described state 2 could be entered. The voltage levels of the external circuitry could be influenced, eventually leading to a temporary wrong diagnosis. Hence it is mandatory to initialize the device if the application requires monitoring of voltage levels in standby mode (EN=LOW) after the first VS ramp up. Normal operation (EN=HIGH) is not influenced. Later standby modes are also not influenced. Once the device is initialized properly, the resistive output versus ground is always present (figure 1) in standby mode.
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3 Proposed initialization sequences for L9903:
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Proposed initialization sequences for L9903:
Vs > 7V EN = High PWM = Low DIR = High DIR = Low for >50s after 50s of EN for >10s after min 50s of EN for >10s after min 10s DIR = High after min 50s of EN after 50s of EN positive Edge after min 50s of EN for >10s after min 50s of EN for >10s after min 10s DIR = Low after min 50s of EN
Alternative 1:
Alternative 2:
Vs > 7V EN = High PWM = Low DIR = Low DIR = High
Figure 4.
Proposed Sequence to Initialize L9903 after VS is applied
VS should be >7V before EN=HI VS
> 50 u s
EN
> 10 u s
> 10 u s
PWM DIR
Alternative 1: pos. Pulse at DIR with PWM=0
PWM DIR
Alternative 2: neg. Pulse at DIR with PWM=0
Two possible solutions. Important is that after enabling the L9903 both LS transistors willb be switched-on (Sx forced o GND) for at least 10s (Cboot=100nF) to allow boostrap capacitor to be charged. This is realized by changing the DIR-input while PWM is low. The min 50s delay are needed for the internal circuit to setup. A signal change within the 50s may not be detected.
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4 Proposed initialization sequences L9904:
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Proposed initialization sequences L9904:
Vs > 7V EN = High PWM = Low Pulse PWM = 1 for >50s after 50s of EN for >10s for >50s positive Edge after min 50s of EN for >10s
Alternative 1:
Alternative 2:
Vs > 7V EN = High PWM = Edge PWM = 1 Vs > 7V EN = High PWM = 1 DIR=Edge
Alternative 3:
for >50s for >10s after Edge of DIR 50s of EN after 50s of EN
Figure 5.
Proposed Sequence to Initialize L9904 after VS is applied
VS should be>7V before EN=HI >10us VS >50us EN PWM >10us PWM PWM DIR Alternative 2: pos. Edge PWM >10us Alternative 3: Edge at DIR with PWM=1 EN Alternativ 1: Pulse at PWM
Three possible solutions. Important is that PWM=1 will be detected after enabling the L9904 to switch on both LS transistors (break mode). Therefore an edge at PWM or DIR input has to be present 50s (or more) after EN was set HI. The 50s delay are needed for the internal circuit to setup. A signal change within the 50s may not be detected. After this edge the PWM should be HI for at least 10s (CBoot= 100nF) to charge the CBx bootsstrap capacitors (depending on value of capacitor)
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Revision history
Da te October 2005 Revision 1 Initial release. Cha nge s
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5 Revision history
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