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33981B Datasheet(PDF) 26 Page - Freescale Semiconductor, Inc |
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33981B Datasheet(HTML) 26 Page - Freescale Semiconductor, Inc |
26 / 37 page Analog Integrated Circuit Device Data 26 Freescale Semiconductor 33981 TYPICAL APPLICATIONS POWER DISSIPATION CISPR 25 standard as shown in Figure 31. The tested board was the EMC enhanced board. Figure 31. Radiated Emission Test Set Up The results of these measurements are represented in Figure 32. The enhanced board is in accordance with the Class 3 limits of the CISPR25 standard for radiated emission. Figure 32. Radiated Emission Spectrum for 33981 CONCLUSION This document explains how to measure conducted and radiated emission in accordance with the automotive CISPR25 standard. Measurements were performed on the 33981 in real application conditions when driving an inductive load. An optimized filtering solution was put in place to have the tested system in accordance with the Class 3 limits. The same method can be used with other PC boards. POWER DISSIPATION INTRODUCTION This section relates to the power dissipation capability for 33981, High Frequency High-Current High-Side Switch. This device is a self-protected silicon switch used to replace electromechanical relays, fuses, and discrete circuits in power management applications. This section presents the key features of the device and its targeted applications. The theoretical calculations for power dissipation and die junction temperatures are determined in this document for inductive loads. A concrete example with DC motor driven by the 33981 is analyzed in section DC Motor 200 W. DEVICE FEATURES This 33981 is a 4.0 m Ω self-protected, high-side switch digitally controlled from a microcontroller (MCU) with extended diagnostics, able to drive DC motors up to 60 kHz. A bootstrap architecture has been used to provide fast transient gate voltage in order to reach 4.0 m Ω R DS(ON) maximum at room temperature. In parallel, a charge pump is implemented to offer continuous on-state capability. This dual current supply of the high-side MOSFET allows a duty cycle from 5% to 100%. An external capacitor connected between pins SR and GND is used to control the slew rate at the output and, therefore, reduce electromagnetic perturbations. In standard configuration, the motor current recirculation is handled by an external freewheeling diode. To reduce global power dissipation, the freewheeling diode can be replaced by an external discrete MOSFET in low-side configuration. The IC integrates a gate driver that controls and protects this external MOSFET in the event of short circuit to battery. The product manages the cross conduction between the internal high side and the external low side when used in a half bridge configuration. The two MOSFETs can be controlled independently when the CONF pin is at 0 V. To eliminates fuses, the device is self-protected from severe short-circuits (100 A typical) with an innovative overcurrent strategy. The 33981 has a current feedback for real-time monitoring of the load current through an MCU analog/digital converter to facilitate closed-loop operation for motor speed control. The 33981 has an analog thermal feedback that can be used by the MCU to monitor PC board temperature to optimize the motor control and to protect the entire electronic system. Therefore, an over temperature shutdown feature protects the IC against high overload condition. 1.5 m Length of Cable LISN and Inductive Load 1 m Vertical Monopole Antenna Anechoic Chamber EUT CISPR Class 3 Limits 33981 Emission |
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