TL H 5062
LM1949
Injector
Drive
Controller
February 1995
LM1949 Injector Drive Controller
General Description
The LM1949 linear integrated circuit serves as an excellent
control of fuel injector drive circuitry in modern automotive
systems The IC is designed to control an external power
NPN Darlington transistor that drives the high current injec-
tor solenoid The current required to open a solenoid is sev-
eral times greater than the current necessary to merely hold
it open therefore the LM1949 by directly sensing the actu-
al solenoid current initially saturates the driver until the
``peak'' injector current is four times that of the idle or ``hold-
ing'' current
(Figure 3 Figure 7) This guarantees opening
of the injector The current is then automatically reduced to
the sufficient holding level for the duration of the input
pulse In this way the total power consumed by the system
is dramatically reduced Also a higher degree of correlation
of fuel to the input voltage pulse (or duty cycle) is achieved
since opening and closing delays of the solenoid will be
reduced
Normally powered from a 5V
g
10% supply the IC is typi-
cally operable over the entire temperature range (
b
55 C to
a
125 C ambient) with supplies as low as 3 volts This is
particularly useful under ``cold crank'' conditions when the
battery voltage may drop low enough to deregulate the
5-volt power supply
The LM1949 is available in the plastic miniDIP (contact fac-
tory for other package options)
Features
Y
Low voltage supply (3V 5 5V)
Y
22 mA output drive current
Y
No RFI radiation
Y
Adaptable to all injector current levels
Y
Highly accurate operation
Y
TTL CMOS compatible input logic levels
Y
Short circuit protection
Y
High impedance input
Y
Externally set holding current I
H
Y
Internally set peak current (4
c
I
H
)
Y
Externally set time-out
Y
Can be modified for full switching operation
Y
Available in plastic 8-pin miniDIP
Applications
Y
Fuel injection
Y
Throttle body injection
Y
Solenoid controls
Y
Air and fluid valves
Y
DC motor drives
Typical Application Circuit
TL H 5062 1
FIGURE 1 Typical Application and Test Circuit
Order Number LM1949M or LM1949N
See NS Package Number M08A or N08E
COPS
TM
is a trademark of National Semiconductor Corporation
C1995 National Semiconductor Corporation
RRD-B30M115 Printed in U S A
Absolute Maximum Ratings
If Military Aerospace specified devices are required
please contact the National Semiconductor Sales
Office Distributors for availability and specifications
Supply Voltage
8V
Power Dissipation (Note 1)
1235 mW
Input Voltage Range
b
0 3V to V
CC
Operating Temperature Range
b
40 C to
a
125 C
Storage Temperature Range
b
65 C to
a
150 C
Junction Temperature
150 C
Lead Temp (Soldering 10 sec )
260 C
Electrical Characteristics
(V
CC
e
5 5V V
IN
e
2 4V T
j
e
25 C
Figure 1 unless otherwise specified )
Symbol
Parameter
Conditions
Min
Typ
Max
Units
I
CC
Supply Current
Off
V
IN
e
0V
11
23
mA
Peak
Pin 8
e
0V
28
54
mA
Hold
Pin 8 Open
16
26
mA
V
OH
Input On Level
V
CC
e
5 5V
1 4
2 4
V
V
CC
e
3 0V
1 2
1 6
V
V
OL
Input Off Level
V
CC
e
5 5V
1 0
1 35
V
V
CC
e
3 0V
0 7
1 15
V
I
B
Input Current
b
25
3
a
25
m
A
I
OP
Output Current
Peak
Pin 8
e
0V
b
10
b
22
mA
Hold
Pin 8 Open
b
1 5
b
5
mA
V
S
Output Saturation Voltage
10 mA V
IN
e
0V
0 2
0 4
V
Sense Input
V
p
Peak Threshold
V
CC
e
4 75V
350
386
415
mV
V
H
Hold Reference
88
94
102
mV
t
Time-out t
t
d
R
T
C
T
90
100
110
%
NOTE 1
For operation in ambient temperatures above 25 C the device must be derated based on a 150 C maximum junction temperature and a thermal
resistance of 100 C W junction to ambient
Typical Circuit Waveforms
TL H 5062 2
2
Schematic Diagram
TLH5062
3
FIGURE
2
LM1949
Circuit
3
Typical Performance Characteristics
Quiescent Current vs
Supply Voltage
Supply Current vs
Supply Voltage
Output Current vs
Supply Voltage
Input Voltage Thresholds
vs Supply Voltage
Sense Input Peak Voltage
vs Supply Voltage
Sense Input Hold Voltage
vs Supply Voltage
Normalized Timer Function
vs Supply Voltage
Quiescent Supply Current
vs Junction Temperature
Quiescent Supply Current
vs Junction Temperature
Output Current vs
Junction Temperature
Input Voltage Thresholds
vs Junction Temperature
Sense Input Peak Voltage
vs Junction Temperature
TL H 5062 4
4
Typical Performance Characteristics
(Continued)
Sense Input Hold Voltage
vs Junction Temperature
Normalized Timer Function
vs Junction Temperature
LM1949N Junction
Temperature Rise Above
Ambient vs Supply Voltage
TL H 5062 5
Application Hints
The injector driver integrated circuits were designed to be
used in conjunction with an external controller The LM1949
derives its input signal from either a control oriented proces-
sor (COPS
TM
) microprocessor or some other system This
input signal in the form of a square wave with a variable
duty cycle and or variable frequency is applied to Pin 1 In
a typical system input frequency is proportional to engine
RPM Duty cycle is proportional to the engine load The cir-
cuits discussed are suitable for use in either open or closed
loop systems In closed loop systems the engine exhaust is
monitored and the air-to-fuel mixture is varied (via the duty
cycle) to maintain a perfect or stochiometric ratio
INJECTORS
Injectors and solenoids are available in a vast array of sizes
and characteristics Therefore it is necessary to be able to
design a drive system to suit each type of solenoid The
purpose of this section is to enable any system designer to
use and modify the LM1949 and associated circuitry to
meet the system specifications
Fuel injectors can usually be modeled by a simple RL circuit
Figure 3 shows such a model for a typical fuel injector In
actual operation the value of L
1
will depend upon the status
of the solenoid In other words L
1
will change depending
TL H 5062 6
FIGURE 3 Model of a Typical Fuel Injector
upon whether the solenoid is open or closed This effect if
pronounced enough can be a valuable aid in determining
the current necessary to open a particular type of injector
The change in inductance manifests itself as a breakpoint in
the initial rise of solenoid current The waveforms on Page 2
at the sense input show this occurring at approximately 130
mV Thus the current necessary to overcome the constric-
tive forces of that particular injector is 1 3 amperes
PEAK AND HOLD CURRENTS
The peak and hold currents are determined by the value of
the sense resistor R
S
The driver IC when initiated by a
logic 1 signal at Pin 1 initially drives Darlington transistor Q
1
into saturation The injector current will rise exponentially
from zero at a rate dependent upon L
1
R
1
the battery volt-
age and the saturation voltage of Q
1
The drop across the
sense resistor is created by the solenoid current and when
this drop reaches the peak threshold level typically 385 mV
the IC is tripped from the peak state into the hold state The
IC now behaves more as an op amp and drives Q
1
within a
closed loop system to maintain the hold reference voltage
typically 94 mV across R
S
Once the injector current drops
from the peak level to the hold level it remains there for the
duration of the input signal at Pin 1 This mode of operation
is preferable when working with solenoids since the current
required to overcome kinetic and constriction forces is often
a factor of four or more times the current necessary to hold
the injector open By holding the injector current at one
fourth of the peak current power dissipation in the sole-
noids and Q
1
is reduced by at least the same factor
In the circuit of
Figure 1 it was known that the type of injec-
tor shown opens when the current exceeds 1 3 amps and
closes when the current then falls below 0 3 amps In order
to guarantee injector operation over the life and tempera-
ture range of the system a peak current of approximately 4
amps was chosen This led to a value of R
S
of 0 1X Divid-
ing the peak and hold thresholds by this factor gives peak
and hold currents through the solenoid of 3 85 amps and
0 94 amps respectively
Different types of solenoids may require different values of
current The sense resistor R
S
may be changed accordingly
An 8-amp peak injector would use R
S
equal to 05X etc
Note that for large currents above one amp IR drops within
the component leads or printed circuit board may create
substantial errors unless appropriate care is taken The
sense input and sense ground leads (Pins 4 and 5 respec-
tively) should be Kelvin connected to R
S
High current
should not be allowed to flow through any part of these
traces or connections An easy solution to this problem on
double-sided PC boards (without plated-through holes) is to
have the high current trace and sense trace attach to the
R
S
lead from opposite sides of the board
TIMER FUNCTION
The purpose of the timer function is to limit the power dissi-
pated by the injector or solenoid under certain conditions
Specifically when the battery voltage is low due to engine
cranking or just undercharged there may not be sufficient
voltage available for the injector to achieve the peak cur-
rent In the
Figure 2 waveforms under the low battery condi-
tion the injector current can be seen to be leveling out at 3
5
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