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L6743TR Folha de dados(PDF) 9 Page - STMicroelectronics |
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L6743TR Folha de dados(HTML) 9 Page - STMicroelectronics |
9 / 17 page L6743, L6743Q Device description and operation 9/17 5.3 Internal BOOT diode L6743, L6743Q embeds a boot diode to supply the high-side driver saving the use of an external component. Simply connecting an external capacitor between BOOT and PHASE complete the high-side supply connections. To prevent bootstrap capacitor to extra-charge as a consequence of large negative spikes, an external series resistance RBOOT (in the range of few ohms) may be required in series to BOOT pin. Bootstrap capacitor needs to be designed in order to show a negligible discharge due to the high-side MOSFET turn-on. In fact it must give a stable voltage supply to the high-side driver during the MOSFET turn-on also minimizing the power dissipated by the embedded Boot Diode. Figure 5 gives some guidelines on how to select the capacitance value for the bootstrap according to the desired discharge and depending on the selected MOSFET. Figure 5. Bootstrap capacitance design 5.4 Power dissipation L6743, L6743Q embeds high current drivers for both high-side and low-side MOSFETs: it is then important to consider the power that the device is going to dissipate in driving them in order to avoid overcoming the maximum junction operative temperature. Two main terms contribute in the device power dissipation: bias power and drivers' power. ● Device power (PDC) depends on the static consumption of the device through the supply pins and it is simply quantifiable as follow: ● Drivers' power is the power needed by the driver to continuously switch ON and OFF the external MOSFETs; it is a function of the switching frequency and total gate charge of the selected MOSFETs. It can be quantified considering that the total power PSW dissipated to switch the MOSFETs dissipated by three main factors: external gate resistance (when present), intrinsic MOSFET resistance and intrinsic driver resistance. This last term is the important one to be determined to calculate the device power dissipation. The total power dissipated to switch the MOSFETs results: P DC V CC I CC V PVCC I PVCC ⋅ + ⋅ = P SW F SW Q GHS PVCC ⋅ Q GLS VCC ⋅ + () ⋅ = |
Nº de peça semelhante - L6743TR |
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Descrição semelhante - L6743TR |
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