MC33094 View Datasheet(PDF) - Motorola => Freescale

Part Name

Description

Manufacturer

MC33094

Ignition Control

Motorola => Freescale 

Freescale SMeCm3i3c0o94nductor, Inc.

represents an effort to reduce excess dwell and therefore

power dissipation during high voltage operation. The 5.88 µA

discharge rate is used under normal VCC operating

conditions. Under a start mode, this block will discharge the

adaptive capacitor forcing an enhanced start mode dwell.

The start/run modes are set internally by detecting the engine

frequency, which corresponds to the ramp capacitor voltage.

The Stall Capacitor Charging and Sensing block controls

the charging and discharging rates of the stall capacitor. The

charging rate is 31.5 µA, and the two discharging rates are

1.0 µA and 7.0 µA. The stall capacitor potential commands

the IC to maintain or reduce the coil current. When the engine

is turning very slowly (or stalled), the stall capacitor will have

enough time to discharge below threshold and thereby

reduce coil current. The output current limiter (see Output

Current Driver and Limiter block description below) forces the

coil current to be proportional to the stall capacitor voltage

when the stall capacitor voltage is less than 2.0 V.

The Ramp Capacitor Charging and Sensing block charges

the ramp capacitor at approximately 8.4 µA and discharges it

at about 33.6 µA. The charging circuit is always on and

sources current during the “not 25%” part of the engine cycle.

The discharging circuit is only on and sinking current during

the “25%” part of the engine cycle. The positive edge of the

distributor input signal sets the 25% mode, and the ramp

comparator output clears this mode.

The CR > CA Adaptive Comparator block signals the point

where the ramp capacitor voltage is greater than the adaptive

capacitor voltage. The point at which the two capacitor

voltages are equal is the point where charging of the coil is

begun. The adaptive algorithm used in the IC maintains the

required excess dwell throughout all reasonable

accelerations and decelerations without causing excess coil

power dissipation, in addition, it insures that more than

adequate spark energy is available for very high engine

speeds, when excess dwell is impossible.

The Output Current Driver and Limiter block sources a

limited supply current of about 50 mA to the base of the

Darlington power transistor. The Darlington will cause the

coil to conduct to about 6.5 amps and the voltage drop on

the IS pin of the IC will rise to the threshold of the current

limiter. The current limiter will then hold the coil current at that

level until either a spark is commanded by the logic block, or

the engine begins to stall (causing the coil to slowly

discharge).

The Internal Logic block performs the required memory

and gating functions on the IC to implement the adaptive

ignition control algorithm.

2 MB

Figure 10. Block Diagram

6 Gnd

9 VCC

Master Bias

Vr

Current

Reference

BG

Master Bias

Band Gap

Reference

Dump

Vr

Hi-Bat.

Vr Zener

Reference

Vr

VCC

VCC

Comparator

and Clamp

10

DS

Input

Voltage

7

Comparator

Vin(-)

Output Current

12

Driver and

Limiter

Out

ZC

Limit

Internal

11

Negative

Logic

CL

Edge Filter

8

14

Stall

ST

S

13

Stall

25% 25%

Reset

T

3

Adaptive Capacitor

CR > CA

CA

Charging and Sensing

CA

CR > CA

Master Bias

Vr

CR

Adaptive

Comparator

Master

Bias

Stall BG

Stall Capacitor

4

Ramp Capacitor

CR

Charging and Sensing

BG

Vr

25% Reset 25%

Charging

and Sensing

15 CS

MOTOROLA ANALOG IC DEVICE FDoATrAMore Information On This Product,

9

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