Analog Integrated Circuit Device Data

28

Freescale Semiconductor

33874

TYPICAL APPLICATION

INTRODUCTION

TYPICAL APPLICATION

INTRODUCTION

The 33874 can be configured in several applications. The figure below shows the 33874 in a typical lighting application.

33874

I/O

GND

Microcontroller

Voltage regulator

100nF

HS2

HS0

HS1

HS3

WAKE

FS

IN0

IN2

IN3

SCLK

CS

NC

TEMP

SI

SO

FSI

RST

IN1

10µF

100nF

I/O

I/O

I/O

I/O

I/O

SCLK

CS

SI

SO

A/D

10k

10k

10k

10k

10k

10k

10k

10k

10k

1k

R1

10k

LOAD 0

LOAD 1

LOAD 2

LOAD 3

CSNS

A/D

21W

5W

21W

5W

21W

5W

21W

5W

Automotive lamps do not tolerate high voltages very well. Tests of a few lamps indicate that failures can occur when

18V is applied for a few seconds. Consequently, PWM switching reduces the effective RMS voltage in order to drive

bulbs safety.

For example, to maintain the power dissipation associated with a 13V battery at 100% duty cycle, the duty cycle

would be adjusted to (13/18)², or 52%, when the battery is at 18V.

The loads must be chosen in order to guarantee the device normal operating condition as junction temperature

from -40 to 150 °C. In case of permanent short-circuit conditions, the duration and number of activation cycles must

be limited with a dedicated MCU fault management using the fault reporting through SPI.