3

Inductive actuators such as automotive electronic fuel

injectors, relays, solenoids and hammer drivers can be

powered more efficiently by providing a high current

drive until actuation (pull-in) occurs and then decreasing

the drive current to a level which will sustain actuation.

Pull-in and especially dropout times of the actuators are

also improved.

The fundamental output characteristic of the CS452/453

provides a low impedance saturated power switch until

the load current reaches a predetermined high-current

level and then changes to a current source of lower magni-

tude until the device is turned off. This output characteris-

tic allows the inductive load to control its actuation time

during turn-on while minimizing power and stored energy

during the sustain period, thereby promoting a fast turn-

off time.

Automotive injectors at present time come in two types.

The large throttle body injectors have an inductance of

about 2.0mH and an impedance of 1.2

Ω and require the

CS453 driver. The smaller type, popular worldwide, have

an inductance of 4.0mH and an impedance of 2.4

Ω and

needs about a 2.0A pulse for good results, which can be

met with the CS452. Some designs are planned which

employ two of the smaller types in parallel. The induc-

tance of the injectors are much larger at low current,

decreasing due to armature movement and core saturation

to the values above at rated current.

Operating frequencies range from 5.0Hz to 250Hz depend-

ing on the injector location and engine type. Duty cycle in

some designs reaches 80%.

Figure 1. Operating Waveforms (Max. Frequency 250Hz, CONTROL

Grounded)

Circuit Description

>1.4V

0

2.0

4.0ms

Input Signal

Load

Current

Output

Current

Output

Voltage

Power

Dissipation

Timing Diagrams

Input Voltage and Output Current vs. Time

4

5

0

3

1

0

10

10

9

8

7

6

5

4

3

2

1

0

CS453

2

2.4

5

0

1.8

0.6

0

10

10

9

8

7

6

5

4

3

2

1

0

CS452

1.2