MC33094

10

MOTOROLA ANALOG IC DEVICE DATA

SW

Ignition

Master

Bias

Band-Gap

Reference

Zener Ref.

Input

Comp. and

Negative

Edge Filter

Output Current

Driver and Limiter

Stall

Capacitor

Adaptive

Capacitor

Ramp

Capacitor

CR > CA

Comparator

Internal

Logic

26

9

CA

CR

CS

ST

T

10

12

11

14

15.3 k

330

55

18 V

200

4.0 k

200

56

0.05

5.0 W

0.1 µ

27 k

10 k

Figure 11. Typical Ignition Circuit

7

8

13

MB

G

0.1 µ

0.1 µ

DI

Out

DC

IS

34

15

0.1 µ

0.1 µ

BU931,

MJE5742,

or

MJH10012

Introduction

The MC33094DW is designed for engine compartment

use in 12 V automotive ignition applications to provide high

performance control of the ignition coil when used with an

appropriate Motorola Power Darlington Transistor. Engine

control systems utilizing these devices for ignition coil control

exhibit superior fuel efficiency and lower exhaust emissions

over predecessor systems. The device is designed for single

input control from a Hall sensor to determine crankshaft

position.

The device, a bipolar linear integrated circuit, is built using

high–density Integrated–Injection Logic (IIL) processing

incorporating high current–gain PNP and NPN transistors. All

module inputs are transient voltage protected through the

use of resistors, capacitors, and/or zener diodes working in

conjunction with internal protection elements. These

elements provide protection of critical circuitry from externally

induced high–voltage transients which may degrade the

devices operational performance. At the module level, it is

decoupled using an external resistor and capacitor to work in

conjunction with the on–chip internal zener string to provide

robust module protection of the device power pin. The D input

of module should be protected from transients through the

use of an external resistor and zener diode. The Start Wire of

the module should be decoupled through the use of two

resistors and a capacitor to work in conjunction with the

on–chip internal clamp (Figure 11).

The output of the device incorporates a high current–gain

PNP designed to drive an external power Darlington

transistor to provide control of the ignition coil. The output

drive is carefully synchronized with the output from the

distributor. The charging and discharging of three capacitors,

external to the device, provide timing signals which program

the dwell and charge time control of the ignition coil over a

wide rpm range.

The timing and charge/discharge rates of the three

external capacitors are accurately controlled by internal

circuitry acted upon by sensor and distributor signal detection

of the device.

A feedback path from the emitter of the external power

Darlington transistor to the device provide monitoring of the

ignition coil current. An internal comparitor of the device

senses and limits the maximum ignition coil current to

approximately 6.5 amps. Other circuitry within the device

provides an interruption of the coil current so as to generate

the spark, or slowly discharges the coil in a controlled

manner so as to prevent a spark and limit the total module

energy dissipation.

When the external Darlington is switched off, the

Darlington collector will instantly experience a dramatic

increase in voltage as a result of the collapsing field of the

ignition coil (inductive kick). The external voltage divider

working in conjunction with the internal device zener string

and power PNP form a dynamic clamp which limits the

inductive kick voltage to less than 350 V. This feature

protects the Darlington transistor from damaging stress or

breakdown.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com