TYPICAL APPLICATIONS
POWER DISSIPATION
CISPR 25 standard as shown in Figure 31. The tested board
was the EMC enhanced board.
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.
1.5 m Length
of Cable
Anechoic
Chamber
CISPR
Class 3
Limits
LISN and
Inductive Load
33981
Emission
EUT
1 m Vertical
Monopole
Antenna
Figure 32. Radiated Emission Spectrum for 33981
CONCLUSION
Figure 31. Radiated Emission Test Set Up
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
between pins SR and GND is used to control the slew rate at
the output and, therefore, reduce electromagnetic
perturbations.
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.
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
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.
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.
DEVICE FEATURES
This 33981 is a 4.0 mΩ self-protected, high-side switch
digitally controlled from a microcontroller (MCU) with
extended diagnostics, able to drive DC motors up to 60 kHz.
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.
A bootstrap architecture has been used to provide fast
transient gate voltage in order to reach 4.0 mΩ RDS(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
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.
33981
Analog Integrated Circuit Device Data
Freescale Semiconductor
26
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