LM1949N

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 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 g 10% supply the IC is typically operable over the entire temperature range (b55 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 factory for other package options) Features Y Y Y Y Y Y Y Y Y Y Y Y Y Low voltage supply (3V – 5 5V) 22 mA output drive current No RFI radiation Adaptable to all injector current levels Highly accurate operation TTL CMOS compatible input logic levels Short circuit protection High impedance input Externally set holding current IH Internally set peak current (4 c IH) Externally set time-out Can be modified for full switching operation Available in plastic 8-pin miniDIP Applications Y Y Y Y Y Fuel injection Throttle body injection Solenoid controls Air and fluid valves 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 COPSTM is a trademark of National Semiconductor Corporation C1995 National Semiconductor Corporation TL H 5062 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 Power Dissipation (Note 1) 8V 1235 mW Input Voltage Range Operating Temperature Range Storage Temperature Range Junction Temperature Lead Temp (Soldering 10 sec ) b 0 3V to VCC b 40 C to a 125 C b 65 C to a 150 C 150 C 260 C Electrical Characteristics (VCC e 5 5V Symbol ICC Parameter Supply Current Off Peak Hold Input On Level Input Off Level Input Current Output Current Peak Hold Output Saturation Voltage Sense Input Peak Threshold Hold Reference Time-out t VIN e 2 4V Tj e 25 C Figure 1 unless otherwise specified ) Conditions Min Typ 11 28 16 14 12 10 07 b 25 Max 23 54 26 24 16 Units mA mA mA V V V V VIN e 0V Pin 8 e 0V Pin 8 Open VCC e 5 5V VCC e 3 0V VCC e 5 5V VCC e 3 0V VOH VOL IB IOP 1 35 1 15 3 b 22 b5 a 25 mA mA mA Pin 8 e 0V Pin 8 Open 10 mA VIN e 0V VCC e 4 75V t d RTCT b 10 b1 5 VS Vp VH t 02 350 88 90 386 94 100 04 415 102 110 V mV mV % 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 3 TL H 5062 – 3 FIGURE 2 LM1949 Circuit 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 Sense Input Hold Voltage vs Junction Temperature (Continued) LM1949N Junction Temperature Rise Above Ambient vs Supply Voltage Normalized Timer Function vs Junction Temperature 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 processor (COPSTM ) 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 L1 will depend upon the status of the solenoid In other words L1 will change depending age and the saturation voltage of Q1 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 Q1 within a closed loop system to maintain the hold reference voltage typically 94 mV across RS 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 solenoids and Q1 is reduced by at least the same factor In the circuit of Figure 1 it was known that the type of injector 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 RS of 0 1X Dividing 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 RS may be changed accordingly An 8-amp peak injector would use RS 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 respectively) should be Kelvin connected to RS 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 RS lead from opposite sides of the board 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 voltage available for the injector to achieve the peak current In the Figure 2 waveforms under the low battery condition the injector current can be seen to be leveling out at 3 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 RS The driver IC when initiated by a logic 1 signal at Pin 1 initially drives Darlington transistor Q1 into saturation The injector current will rise exponentially from zero at a rate dependent upon L1 R1 the battery volt- 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 RTCT) The timer is reset at the end of each input pulse For 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 CT e 0) Leaving RT in place is 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 RT is approximately 1k to 240k The capacitor CT is limited only by 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 (VBE) by 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 Figure 1 The 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 Q1 to ground with an appropriately rated 0 1 mF capacitor This is however rarely necessary FLYBACK ZENER The purpose of zener Z1 is twofold Since the load is inductive a voltage spike is produced at the collector of Q1 anytime 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 Q1 from damaging voltage levels Thus the rated zener voltage at the system peak current must be less than the guaranteed minimum breakdown of Q1 Also even while Z1 is conducting the majority of the injector current during the peak-to-hold transition (see Figure 4 ) Q1 is 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 RS Q1 will be biased to provide exactly that Thus the safe operating area (SOA) of Q1 must include the hold current with a VCE of Z1 volts For systems where this is not desired the zener anode may be reconnected to the top of RS as shown in Figure 5 Since the voltage across the sense resistor now accurately portrays the injector current at all times the error 6 TL H 5062 – 7 FIGURE 4 Circuit Waveforms amplifier keeps Q1 off 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 Z1 is to provide system transient protection Automotive systems are susceptible to a vast array of voltage transients on the battery line Though their duration is usually only milliseconds long Q1 could suffer permanent damage unless buffered by the injector and Z1 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 TL H 5062 – 8 FIGURE 5 Alternate Configuration for Zener Z1 POWER DISSIPATION The power dissipation of the system shown in Figure 1 is 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 values are given in parentheses e Sense Resistor (0 1X) RS VH Vp VZ VBATT L1 R1 n e Sense Input Hold Voltage ( 094V) e Sense Input Peak Voltage ( 385V) e Z1 Zener 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) The LM1949 can be easily modified to function as a switcher Accomplished with the circuit of Figure 7 the only additional components required are two external resistors RA and RB Additionally the zener needs to be reconnected as shown to RS The amount of ripple on the hold current is easily controlled by the resistor ratio of RA to RB RB is kept small so that sense input bias current (typically 0 3 mA) has negligible effect on VH Duty cycle and frequency of oscillation during the hold state are dependent on the injector characteristics RA RB and the zener voltage as shown in the following equations VH Hold Current RS RB VH b  VZ RA Minimum Hold Current RS  J Ripple or DI Hold fo RB 1  VZ  RA RS V RS RA VBATT    1 b BATT L1 RB VZ VZ fo e Hold State Oscillation Frequency  J Duty Cycle of fo f Q1 Power Dissipation PQ n  VBATT  VBATT VZ Component Power Dissipation V  SAT  VH VZ RS E 1 Amp (1 5V) VSAT e Q1 Saturation Volt VBATT  VH n PZ RS PQ n VH Watts RS (VP2 a VH2) Watts ((VZ-VBATT)  RS2) 1 V b BATT J Zener Dissipation PZ VZ  L1  f  Injector Dissipation VH2 Watts PI n  R1  RS2 Sense Resistor PR n VH2 Watts RS2 n VP2 Watts RS2 VB  VZ R1 As shown the power dissipation by Q1 in this manner is substantially reduced Measurements made with a thermocouple on the bench indicated better than a fourfold reduction in power in Q1 However the power dissipation of the zener (which is independent of the zener voltage chosen) is increased over the circuit of Figure 1 PRA PR (worst case) SWITCHING INJECTOR DRIVER CIRCUIT The power dissipation of the system and especially of Q1 can be reduced by employing a switching injector driver circuit Since the injector load is mainly inductive transistor Q1 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 Q1 will be reduced A note of caution The large amplitude switching voltages that 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 TL H 5062 – 9 FIGURE 6 Switching Waveforms 7 TL H 5062 – 10 FIGURE 7 Switching Application Circuit 8 Physical Dimensions inches (millimeters) 14-Lead (0 150 Wide) Molded Small Outline Package JEDEC Order Number LM1949M NS Package Number M08A 9 LM1949 Injector Drive Controller Physical Dimensions inches (millimeters) (Continued) Molded Dual-In-Line Package (N) Order Number LM1949N NS Package Number N08E LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMICONDUCTOR CORPORATION As used herein 1 Life support devices or systems are devices or systems which (a) are intended for surgical implant into the body or (b) support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in a significant injury to the user National Semiconductor Corporation 1111 West Bardin Road Arlington TX 76017 Tel 1(800) 272-9959 Fax 1(800) 737-7018 2 A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system or to affect its safety or effectiveness National Semiconductor Europe Fax (a49) 0-180-530 85 86 Email cnjwge tevm2 nsc com Deutsch Tel (a49) 0-180-530 85 85 English Tel (a49) 0-180-532 78 32 Fran ais Tel (a49) 0-180-532 93 58 Italiano Tel (a49) 0-180-534 16 80 National Semiconductor Hong Kong Ltd 13th Floor Straight Block Ocean Centre 5 Canton Rd Tsimshatsui Kowloon Hong Kong Tel (852) 2737-1600 Fax (852) 2736-9960 National Semiconductor Japan Ltd Tel 81-043-299-2309 Fax 81-043-299-2408 National does not assume any responsibility for use of any circuitry described no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications