- 您現(xiàn)在的位置：買(mǎi)賣(mài)IC網(wǎng) > PDF目錄385476 > LM1951 (National Semiconductor Corporation) LM1951 Solid State 1 Amp Switch PDF資料下載
參數(shù)資料
| 型號(hào)： | LM1951 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | LM1951 Solid State 1 Amp Switch |
| 中文描述： | LM1951固態(tài)1安培開(kāi)關(guān) |
| 文件頁(yè)數(shù)： | 8/10頁(yè) |
| 文件大?。?/td> | 171K |
| 代理商： | LM1951 |
Application Hints
When inductive loads are turned OFF, they produce a nega-
tive voltage spike. The LM1951 contains a voltage clamp
that limits these spikes to approximately
b
30V, thus an ex-
ternal clamp is not necessary in most applications.
Loads with an inductance of greater than 1H, driven to full
output current, may damage the clamp simply by exceeding
the power capabilities of the LM1951. An LM1951 can dissi-
pate 25W continuous at 25
§
C ambient when mounted on a
large heatsink. If the load current is limited to 800 mA, the
sustained spike from an infinitely large inductance can be
handled. Sustained spikes produced by higher currents and
high inductances will exceed the 25W limit.
For inductances above 1H, care should be taken to see that
the output current does not exceed a value that could dam-
age the clamp. While 800 mA is acceptable for the device
running at 25
§
C ambient on a heatsink, derate this current
for smaller heatsinks or higher ambient temperatures to limit
the junction temperature to 150
§
C. Alternatively, an external
clamp or resonating capacitor can be added to handle any
combination of load inductance, load current, and device
temperature. This is especially important if the output cur-
rent is boosted, such as the application shown inFigure 3. A
peak power of 750W could be developed in the internal
clamp if an inductive load is switched without external
clamping.
Another case where the clamp’s power capability may be
exceeded is when driving a solenoid. The inductance of a
solenoid is greatest when energized, with the plunger pulled
in. As the plunger is pulled out of the solenoid, the induc-
tance goes down. Under certain conditions of high solenoid
inductance and fast mechanical time constants, the current
may actually
increase
when the solenoid is turned OFF.
Since the energy stored in an inductor cannot change in-
stantaneously, the current must increase to conserve ener-
gy when the inductance decreases. This condition is traced
by observing the load current with a current probe and stor-
age oscilloscope.
Load capacitances larger than 1 nF will slow rise and fall
times. Inductive loads having a capacitive component larger
than 1 nF will also exhibit overshoot. Furthermore, ringing
may be evident in a combination inductive/capacitive load,
or in an inductive load with supply decoupling capacitors in
the range of 100 nF to 1
m
F. For fast rise and fall times and
minimum ringing with inductive loads, a supply decoupling
capacitor of 10 nF and an output capacitor of 1 nF is recom-
mended. These should be located as close to the IC pins as
possible.
The error flag is an open collector output that pulls low un-
der certain fault conditions. These errors include overvolt-
age (V
CC
l
26V), overcurrent (I
OUT
l
1.3A), undercurrent
(I
OUT
k
2 mA), output short circuit to ground, output short
circuit to supply, and junction temperature greater than
150
§
C. By connecting a 2 k
X
resistor from the error flag
output to a 5V supply a logic output to a microprocessor is
provided.
The error flag can give seemingly false indications in a num-
ber of situations. Slewing large capacitive loads (
l
100 nF)
can drive the LM1951 into temporary current limit, produc-
ing a momentary error indication. Incandescent lamps and
DC motors require an inrush current that will also cause a
temporary current limit and error indication. Large inductive
loads (
l
50 mH) initially appear as open circuits, falsing the
error flag. The error flag pulses for about 1
m
s when any
load is turned ON since the output is initially at ground. In
microprocessor systems these false indications are easily
ignored in software. In discrete logic circuits utilizing a latch
at the error flag output, some filtering may be required.
An internal current sink (10
m
A minimum) is connected to
the input, pin 5. If this pin is left open it is guaranteed to pull
low, switching the LM1951 OFF. This characteristic is im-
portant under certain fault conditions such as when the con-
trol line fails open cirucit.
Although the input threshold has hysteresis, the switch
points are derived from a very stable band-gap reference. In
many applications, such as Figures 5 and 7, the LM1951
input can replace an extenal reference and comparator.
The input (pin 5) is clamped at
b
0.7V and includes a series
resistance of approximately 30 k
X
. This pin tolerates nega-
tive inputs of up to 1 mA without affecting the performance
of the chip.
8
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LM1951T | LM1951 Solid State 1 Amp Switch |
| LM195H | Ultra Reliable Power Transistors |
| LM195K | Ultra Reliable Power Transistors |
| LM295 | Ultra Reliable Power Transistors |
| LM295H | Ultra Reliable Power Transistors |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM1951T | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:LM1951 Solid State 1 Amp Switch |
| LM195H | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Ultra Reliable Power Transistors |
| LM195H WAF | 制造商:Texas Instruments 功能描述: |
| LM195H/883 | 制造商:Texas Instruments 功能描述:Trans GP BJT NPN 42V 3-Pin TO-39 Tray |
| LM195K | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Ultra Reliable Power Transistors |
發(fā)布緊急采購(gòu)，3分鐘左右您將得到回復(fù)。