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參數(shù)資料
| 型號(hào)： | LM1949M |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 外設(shè)及接口 |
| 英文描述： | LM1949 Injector Drive Controller |
| 中文描述： | 0.022 A BUF OR INV BASED PRPHL DRVR, PDSO8 |
| 封裝： | 0.150 INCH, SO-8 |
| 文件頁(yè)數(shù)： | 6/10頁(yè) |
| 文件大?。?/td> | 214K |
| 代理商： | LM1949M |
Timer Function
(Continued)
amps, or 1 amp below the normal threshold. Since continu-
ous 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
T
C
T
). 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., C
T
e
0). Leaving R
T
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 proba-
bly never vary much from the 3.9 milliseconds shown in
Figure 1. However, the actual useful range of the timer ex-
tends from microseconds to seconds, depending on the
component values chosen. The useful range of R
T
is ap-
proximately 1k to 240k. The capacitor C
T
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 (V
BE
) by
discharging it with a current of approximately 15 mA. Thus,
a 0.1
m
F cap is reset in approximately 25
m
s.
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 pow-
er 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
m
F work well with the circuit of Figure 1. The
value shown of .01
m
F (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
1
to ground with an
appropriately rated 0.1
m
F capacitor. This is, however, rarely
necessary.
FLYBACK ZENER
The purpose of zener Z
1
is twofold. Since the load is induc-
tive, a voltage spike is produced at the collector of Q
1
any-
time the injector current is reduced. This occurs at the peak-
to-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
1
from damaging
voltage levels. Thus, the rated zener voltage at the system
peak current must be less than the guaranteed minimum
breakdown of Q
1
. Also, even while Z
1
is conducting the
majority of the injector current during the peak-to-hold tran-
sition (see Figure 4), Q
1
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 R
S
, Q
1
will be
biased to provide exactly that. Thus, the safe operating area
(SOA) of Q
1
must include the hold current with a V
CE
of Z
1
volts. For systems where this is not desired, the zener an-
ode may be reconnected to the top of R
S
as shown in Fig-
ure 5. Since the voltage across the sense resistor now ac-
curately portrays the injector current at all times, the error
TL/H/5062–7
FIGURE 4. Circuit Waveforms
amplifier keeps Q
1
off until the injector current has decayed
to the proper value. The disadvantage of this particular con-
figuration is that the ungrounded zener is more difficult to
heat sink if that becomes necessary.
The second purpose of Z
1
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, Q
1
could suffer
permanent damage unless buffered by the injector and Z
1
.
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 Z
1
6
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM1949N | 功能描述:開(kāi)關(guān)變換器、穩(wěn)壓器與控制器 RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開(kāi)關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| LM1949N/NOPB | 功能描述:開(kāi)關(guān)變換器、穩(wěn)壓器與控制器 RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開(kāi)關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| LM1949N/NOPB | 制造商:Texas Instruments 功能描述:Power Driver IC |
| LM194C | 制造商:Texas Instruments 功能描述: |
| LM194H/883 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:LM194/LM394 Supermatch Pair |
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