33981B datasheet(26/37 Pages) FREESCALE

Part #	33981B

Description	Single High-Side Switch (4.0 m??, PWM clock up to 60kHz

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Manufacturer	FREESCALE [Freescale Semiconductor, Inc]

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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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33981B Datasheet(PDF) 26 Page - Freescale Semiconductor, Inc

33981B Datasheet(HTML) 26 Page - Freescale Semiconductor, Inc

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