Circuit Description
Inductive actuators such as automotive electronic fuel
Input Signal
IN
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.
V
>1.4V
0
2.0
4.0ms
Load
Current
Ipk
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.
Ipk
Ipk (SENSE)
Output
Current
Isus
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 1.2½ and require the
CS453 driver. The smaller type, popular worldwide, have
an inductance of 4.0mH and an impedance of 2.4½ 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.
ti
tp
td
Output
VZ
Voltage
VBAT
VBAT - (Isus RL)
VSAT
VZ Ipk
Power
Dissipation
VZ Isus
Operating frequencies range from 5.0Hz to 250Hz depend-
ing on the injector location and engine type. Duty cycle in
some designs reaches 80%.
(VBAT - Isus RL) Isus
VSAT Ipk
Figure 1. Operating Waveforms (Max. Frequency 250Hz, CONTROL
Grounded)
Timing Diagrams
Input Voltage and Output Current vs. Time
CS453
CS452
10
5
10
5
4
3
2
1
0
2.4
1.8
1.2
0.6
0
0
0
IOUT
IOUT
0
1
2
3
4
5
6
7
8
9
10
0
1
2
3
4
5
6
7
8
9
10
3
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
