Datasheet LM1949N Datasheet (NSC)

LM1949 Injector Drive Controller

LM1949 Injector Drive Controller

February 1995

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 injec­tor solenoid. The current required to open a solenoid is sev­eral times greater than the current necessary to merely hold
it open; therefore, the LM1949, by directly sensing the actu­al solenoid current, initially saturates the driver until the
‘‘peak’’ injector current is four times that of the idle or ‘‘hold­ing’’ 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
cally operable over the entire temperature range (

a

125§C ambient) with supplies as low as 3 volts. This is

g

10% supply, the IC is typi-

b

55§Cto

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 fac­tory for other package options).

Typical Application Circuit

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

Y

Internally set peak current (4cIH)

Y

Externally set time-out

Y

Can be modified for full switching operation

Y

Available in plastic 8-pin miniDIP

H

Applications

Y

Fuel injection

Y

Throttle body injection

Y

Solenoid controls

Y

Air and fluid valves

Y

DC motor drives

FIGURE 1. Typical Application and Test Circuit

TL/H/5062– 1

Order Number LM1949M or LM1949N

See NS Package Number M08A or N08E

COPSTMis a trademark of National Semiconductor Corporation.

C

1995 National Semiconductor Corporation RRD-B30M115/Printed in U. S. A.

TL/H/5062

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

Operating Temperature Range

Storage Temperature Range

b

0.3V to V

b

40§Ctoa125§C

b

65§Ctoa150§C

CC

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
Peak Pin 8

e

0V 11 23 mA

IN

e

0V 28 54 mA

Hold Pin 8 Open 16 26 mA

V

OH

V

OL

I

B

I

OP

V

S

Input On Level V

Input Off Level V

Input Current

Output Current

Output Saturation Voltage 10 mA, V

Peak Pin 8
Hold Pin 8 Open

e

5.5V 1.4 2.4 V

CC

e

V

3.0V 1.2 1.6 V

CC

e

5.5V 1.0 1.35 V

CC

e

V

3.0V 0.7 1.15 V

CC

b

25 3

e

0V

e

0V 0.2 0.4 V

IN

b

10

b

1.5

b

22 mA

b

5mA

a

25 mA

Sense Input

V

p

V

H

Peak Threshold V
Hold Reference 88 94 102 mV

t Time-out, t tdRTC

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.

§

e

4.75V 350 386 415 mV

CC

T

90 100 110 %

Typical Circuit Waveforms

TL/H/5062– 2

2

Schematic Diagram

TL/H/5062– 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

Normalized Timer Function
vs Supply Voltage

Output Current vs
Junction Temperature

Sense Input Peak Voltage
vs Supply Voltage

Quiescent Supply Current
vs Junction Temperature

Input Voltage Thresholds
vs Junction Temperature

Sense Input Hold Voltage
vs Supply Voltage

Quiescent Supply Current
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

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 proces­sor (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 cir­cuits 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
of the solenoid. In other words, L

will depend upon the status

1

will change depending

1

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 constric­tive 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
logic 1 signal at Pin 1, initially drives Darlington transistor Q

. The driver IC, when initiated by a

S

into saturation. The injector current will rise exponentially
from zero at a rate dependent upon L

, the battery volt-

1,R1

age and the saturation voltage of Q
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
closed loop system to maintain the hold reference voltage,
typically 94 mV, across R
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 sole­noids and Q

In the circuit of
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 tempera­ture range of the system, a peak current of approximately 4
amps was chosen. This led to a value of R
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
An 8-amp peak injector would use R
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 respec­tively), should be Kelvin connected to R
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

lead from opposite sides of the board.

S

TIMER FUNCTION

The purpose of the timer function is to limit the power dissi­pated 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

1

voltage available for the injector to achieve the peak cur­rent. In the
tion, the injector current can be seen to be leveling out at 3

LM1949N Junction
Temperature Rise Above
Ambient vs Supply Voltage

. The drop across the

1

. Once the injector current drops

S

is reduced by at least the same factor.

1

Figure 1

, it was known that the type of injec-

S

may be changed accordingly.

S

Figure 2

waveforms under the low battery condi-

equal to .05X, etc.

S

S

TL/H/5062– 5

within a

1

of 0.1X . Divid-

. High current

5

Timer Function (Continued)

amps, or 1 amp below the normal threshold. Since continu­ous operation at 3 amps may overheat the injectors, the
timer function on the IC will force the transition into the hold
state after one time constant (the time constant is equal to
R

). The timer is reset at the end of each input pulse. For

TCT

systems where the timer function is not needed, it can be
disabled by grounding Pin 8. For systems where the initial
peak state is not required, (i.e., where the solenoid current
rises immediately to the hold level), the timer can be used to
disable the peak function. This is done by setting the time
constant equal to zero, (i.e., C
recommended. The timer will then complete its time-out and
disable the peak condition before the solenoid current has
had a chance to rise above the hold level.

The actual range of the timer in injection systems will proba­bly never vary much from the 3.9 milliseconds shown in

Figure 1

. However, the actual useful range of the timer ex­tends from microseconds to seconds, depending on the
component values chosen. The useful range of R
proximately 1k to 240k. The capacitor C
stray capacitances for low values and by leakages for large
values.

The capacitor reset time at the end of each controller pulse
is determined by the supply voltage and the capacitor value.
The IC resets the capacitor to an initial voltage (V
discharging it with a current of approximately 15 mA. Thus,
a 0.1 mF cap is reset in approximately 25 ms.

COMPENSATION

Compensation of the error amplifier provides stability for the
circuit during the hold state. External compensation (from
Pin 2 to Pin 3) allows each design to be tailored for the
characteristics of the system and/or type of Darlington pow­er device used. In the vast majority of designs, the value or
type of the compensation capacitor is not critical. Values of
100 pF to 0.1 mF work well with the circuit of
value shown of .01 mF (disc) provides a close optimum in
choice between economy, speed, and noise immunity. In
some systems, increased phase and gain margin may be
acquired by bypassing the collector of Q
appropriately rated 0.1 mF capacitor. This is, however, rarely
necessary.

FLYBACK ZENER

The purpose of zener Z
tive, a voltage spike is produced at the collector of Q
time the injector current is reduced. This occurs at the peak­to-hold transition, (when the current is reduced to one fourth
of its peak value), and also at the end of each input pulse,
(when the current is reduced to zero). The zener provides a
current path for the inductive kickback, limiting the voltage
spike to the zener value and preventing Q
voltage levels. Thus, the rated zener voltage at the system
peak current must be less than the guaranteed minimum
breakdown of Q
majority of the injector current during the peak-to-hold tran­sition (see

. Also, even while Z1is conducting the

1

Figure 4

), Q1is operating at the hold current
level. This fact is easily overlooked and, as described in the
following text, can be corrected if necessary. Since the error
amplifier in the IC demands 94 mV across R
biased to provide exactly that. Thus, the safe operating area
(SOA) of Q
volts. For systems where this is not desired, the zener an-

must include the hold current with a VCEof Z

1

ode may be reconnected to the top of R

ure 5

. Since the voltage across the sense resistor now ac-

curately portrays the injector current at all times, the error

e

0). Leaving RTin place is

T

T

is limited only by

T

BE

Figure 1

to ground with an

1

is twofold. Since the load is induc-

1

from damaging

1

will be

S,Q1

as shown in

S

is ap-

)by

. The

any-

1

Fig-

FIGURE 4. Circuit Waveforms

amplifier keeps Q1off until the injector current has decayed
to the proper value. The disadvantage of this particular con­figuration is that the ungrounded zener is more difficult to
heat sink if that becomes necessary.

The second purpose of Z
protection. Automotive systems are susceptible to a vast

is to provide system transient

1

array of voltage transients on the battery line. Though their
duration is usually only milliseconds long, Q
permanent damage unless buffered by the injector and Z
This is one reason why a zener is preferred over a clamp
diode back to the battery line, the other reason being long
decay times.

1

FIGURE 5. Alternate Configuration for Zener Z

6

TL/H/5062– 7

could suffer

1

TL/H/5062– 8

.

1

1

POWER DISSIPATION

The power dissipation of the system shown in

Figure 1

dependent upon several external factors, including the fre­quency and duty cycle of the input waveform to Pin 1. Cal­culations are made more difficult since there are many dis­continuities and breakpoints in the power waveforms of the
various components, most notably at the peak-to-hold tran­sition. Some generalizations can be made for normal opera­tion. For example, in a typical cycle of operation, the majori­ty of dissipation occurs during the hold state. The hold state
is usually much longer than the peak state, and in the peak
state nearly all power is stored as energy in the magnetic
field of the injector, later to be dumped mostly through the
zener. While this assumption is less accurate in the case of
low battery voltage, it nevertheless gives an unexpectedly
accurate set of approximations for general operation.

The following nomenclature refers to

Figure 1

. Typical val-

ues are given in parentheses:

e

R

V

V

V

V

L

R

n

f

S

H

p

Z

BATT

1

1

Sense Resistor (0.1X)

e

Sense Input Hold Voltage (.094V)

e

Sense Input Peak Voltage (.385V)

e

Z1Zener Breakdown Voltage (33V)

e

Battery Voltage (14V)

e

Injector Inductance (.002H)

e

Injector Resistance (1X)

e

Duty Cycle of Input Voltage of Pin 1 (0 to 1)

e

Frequency of Input (10Hz to 200Hz)

Q1Power Dissipation:

V

BATT

H

Watts

#

R

S

&

P

V

n

#

Q

Zener Dissipation:

2

2

a

(V

V

BATT

H

)#R

)

Watts

2

)

S

&

P

Z

L

V

#

#f#

Z

1

P

((VZ-V

Injector Dissipation:

2

V

&

P

n

I

H

R

#

Watts

#

1

2

R

S

Sense Resistor:

2

V

H

&

P

R

(worst case)&n

P

R

Watts

n

2

R

S

2

V

P

Watts

2

R

S

SWITCHING INJECTOR DRIVER CIRCUIT

The power dissipation of the system, and especially of Q
can be reduced by employing a switching injector driver cir­cuit. Since the injector load is mainly inductive, transistor Q
can be rapidly switched on and off in a manner similar to
switching regulators. The solenoid inductance will naturally
integrate the voltage to produce the required injector cur­rent, while the power consumed by Q
note of caution: The large amplitude switching voltages that

will be reduced. A

1

are present on the injector can and do generate a tremen­dous amount of radio frequency interference (RFI). Because
of this, switching circuits are not recommended. The extra
cost of shielding can easily exceed the savings of reduced
power. In systems where switching circuits are mandatory,
extensive field testing is required to guarantee that RFI can­not create problems with engine control or entertainment
equipment within the vicinity.

is

The LM1949 can be easily modified to function as a switch­er. Accomplished with the circuit of

Figure 7

tional components required are two external resistors, R
and RB. Additionally, the zener needs to be reconnected, as
shown, to R
easily controlled by the resistor ratio of R

. The amount of ripple on the hold current is

S

small so that sense input bias current (typically 0.3 mA) has
negligible effect on V
tion during the hold state are dependent on the injector
characteristics, R
the following equations.

Hold Current

Minimum Hold Current

Ripple or DI Hold

R

R

S

A

&

f

#

o

L

R

1

B

Duty Cycle of f

. Duty cycle and frequency of oscilla-

H

, and the zener voltage as shown in

A,RB

V

H

&

R

S

&

R

B

&

R

A

V

BATT

#

#

V

#

Z

e

f

o

V

BATT

&

o

V

Z

R

B

b

V

#

H

R

#

A

R

S

1

V

#

#

Z

R

S

V

BATT

b

1

V

J

Z

Hold State Oscillation Frequency

Component Power Dissipation

&

P

n

Q

e

V

SAT

&

n

P

Z

&

P

RA

V

b

1

#

#

Q1Saturation Volt

V

#

BATT

#

R

S

V

V

#

B

Z

R

1

BATT

V

Z

V

H

V

SAT

V

#

#

H

R

J

S

@

E

1 Amp (1.5V)

As shown, the power dissipation by Q1in this manner is
substantially reduced. Measurements made with a thermo­couple on the bench indicated better than a fourfold reduc­tion in power in Q
zener (which is independent of the zener voltage chosen) is
increased over the circuit of

,

1

1

. However, the power dissipation of the

1

Figure 1

.

FIGURE 6. Switching Waveforms

, the only addi-

to RB.RBis kept

A

V

Z

J

TL/H/5062– 9

A

7

FIGURE 7. Switching Application Circuit

TL/H/5062– 10

8

Physical Dimensions inches (millimeters)

14-Lead (0.150×Wide) Molded Small Outline Package, JEDEC

Order Number LM1949M

NS Package Number M08A

9

Physical Dimensions inches (millimeters) (Continued)

LM1949 Injector Drive Controller

Molded Dual-In-Line Package (N)

Order Number LM1949N

NS Package Number N08E

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DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL
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systems which, (a) are intended for surgical implant support device or system whose failure to perform can
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failure to perform, when properly used in accordance support device or system, or to affect its safety or
with instructions for use provided in the labeling, can effectiveness.
be reasonably expected to result in a significant injury
to the user.

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