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L6741TR Datenblatt(PDF) 7 Page - STMicroelectronics |
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L6741TR Datenblatt(HTML) 7 Page - STMicroelectronics |
7 / 16 page L6741 Device description and operation 7/16 5 Device description and operation L6741 provides high-current driving control for both High-Side and Low-Side N-Channel MOSFETS connected as Step-Down DC-DC Converter driven by an external PWM signal. The integrated high-current drivers allow using different types of power MOSFETs (also multiple MOS to reduce the equivalent RdsON), maintaining fast switching transition. The driver for the High-Side MOSFET use BOOT pin for supply and PHASE pin for return. The driver for the Low-Side MOSFET use the VCC pin for supply and PGND pin for return. L6741 embodies a anti-shoot-through and adaptive dead-time control to minimize Low-Side body diode conduction time maintaining good efficiency saving the use of external Schottky diodes: when the high-side mosfet turns off, the voltage on its source begins to fall; when the voltage reaches about 2V, the Low-Side MOSFET gate drive voltage is suddenly applied. When the Low-Side MOSFET turns off, the voltage at LGATE pin is sensed. When it drops below about 1V, the High-Side MOSFET gate drive voltage is suddenly applied. If the current flowing in the inductor is negative, the source of highside mosfet will never drop. To allow the Low-Side MOSFET to turn-on even in this case, a watchdog controller is enabled: if the source of the High-Side MOSFET doesn't drop, the Low-Side MOSFET is switched on so allowing the negative current of the inductor to recirculate. This mechanism allows the system to regulate even if the current is negative. Before VCC overcome the UVLO threshold, L6741 keeps firmly-OFF both High-Side and Low-Side MOSFETS then, after the UVLO has crossed, the PWM input keeps the control of the driver operations. If the PWM input is left floating, the internal resistor divider sets the HiZ: both MOSFETS are kept in the OFF state until PWM transition. After UVLO crossing and while in HiZ, the Preliminary-OV protection is activated: if the voltage senses through the PHASE pin overcome about 2V, the Low-Side MOSFET is latched ON in order to protect the load from dangerous over-voltage. The Driver status is reset from a PWM transition. Driver power supply as well as power conversion input are flexible: every combination of 5V and 12V can be chosen for High-Side and Low-Side MOSFET voltage drive. Furthermore, 5V, 12V bus or any intermediate bus that allows the conversion can be chosen freely. Figure 4. Timing diagram thold-off HiZ Window PWM HS Gate LS Gate HiZ Window thold-off |
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