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參數(shù)資料
| 型號(hào)： | LM334 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | 3-Terminal Adjustable Current Sources |
| 中文描述： | 三端可調(diào)電流源 |
| 文件頁數(shù)： | 5/10頁 |
| 文件大?。?/td> | 109K |
| 代理商： | LM334 |
APPLICATION HINT
SLEWRATE
At slew rates above a threshold (see curve) the
LM134,LM234, LM334 can havea non-linearcur-
rentcharacteristic.Theslewrateatwhich thistakes
place is directly proportional to I
set
. At I
set
= 10
μ
A,
dv/dt max. = 0.01V/
μ
S ; at I
set
= 1mA, dv/dt max. =
1V/
μ
S. Slew rates of more than1V/
μ
S do not dam-
age the circuit nor do they producehighcurrents.
THERMAL EFFECTS
Internalheatingcanhaveasignificanteffectoncur-
rent regulation for an I
set
above100
μ
A. For exam-
ple, each increase of 1V in the voltage across the
LM134at I
set
= 1mAwill increase thejunction tem-
peratureby
≈
0.4
o
C (in stillair). The output current
(I
set
) has a temperature coefficient of about
0.33%/
o
C. Thusthe changein current due tothein-
creasein temperaturewill be (0.4)(0.33) =0.132%.
This is a degradationof 10 : 1 in regulationversus
the trueelectrical effects.Thermaleffectsshouldbe
taken into account when d.c. regulation is critical
and I
set
ishigher than100
μ
A. The dissipationof the
connectionsofCB-97packagecanreducethisther-
mal effectby acoefficientof more than3.
SHUNT CAPACITANCE
In certain applications,the15pFvaluefor theshunt
capacitanceshouldbe reduced :
- becauseof loadingproblems,
- becauseof limitation of the output impedance of
the current source in a.c. applications.This reduc-
tion of the capacitancecan be easily carried out by
addingaFETasindicatedinthetypicalapplications.
The valueof this capacitancecanbe reduced byat
least 3pF andregulation can be improved byan or-
derofmagnitudewithoutanymodificationofthed.c.
characteristics (except for the minimum input volt-
age).
NOISE
The current noise produced by LM134, LM234,
LM334 is about 4 times that of a transistor. If the
LM134, LM234,LM334is utilized as an active load
for a transistoramplifier, the noise at the input will
increase by about 12dB. In most cases this is ac-
ceptable,and a single amplifier can be built with a
voltagegainhigher than2000.
LEAD RESISTANCE
The sensevoltage which determines the current of
the LM134,LM234, LM334, is less than 100mV.At
this level, the effects of the thermocouple and the
connectionresistance should be reduced by locat-
ing the current setting resistor close to the device.
Donot usesocketsfortheICs. Acontactresistance
of 0.7
is sufficient to decreasethe output current
by 1%at the 1mAlevel.
SENSINGTEMPERATURE
The LM134, LM234, LM334 are excellent remote
controlled temperature sensors because their op-
erationas sources of current preserves their accu-
racy evenin the caseof longconnectingwires. The
outputcurrentisdirectlyproportionaltotheabsolute
temperaturein degreesKelvinaccording to the fol-
lowing equation.
I
set
=(
227
μ
V/
o
K
) (
T
)
R
set
Thecalibrationof theLM134,LM234,LM334is sim-
plified by the fact that most of the initial accuracy is
dueto gainlimitation (slopeerror) andnotan offset.
Gainadjustmentisaonepointtrimbecausetheout-
putof thedevice extrapolates to zero at 0
o
K.
This particularityof the LM134,LM234,LM334 is il-
lustratedin theabovediagram.Lineabcrepresents
thesensorcurrentbeforeadjustmentandline a’b’c’
representsthedesiredoutput.Anadjustmentof the
gain provided at T2 will move the output from b to
b’and will correcttheslopeat thesametime sothat
theoutputatT1andT3will becorrect.Thisgainad-
justment can be carried out by meansof R
set
or the
load resistor utilized in the circuit. Afteradjustment,
theslope error should be less than1%. A low tem-
peraturecoefficientforR
set
isnecessaryto keepthis
accuracy. A33ppm/
o
C temperaturedrift of R
set
will
givean error of 1% on the slope becausethe resis-
tance follows the same temperature variations as
the LM134, LM234, LM334. Three wires are re-
quired to isolate R
set
from the LM134, LM234,
LM334. Since this solution is not recommended.
Metal-film resistorswith a driftless than 20ppm/
o
C
arenow available.Wirewound resistors canbe util-
ized when very high stabilityis required.
T1
T2
T3
0
°
K
I
set
Desired output
Initial output
c
b
a
a’
b’
c’
LM134-LM234-LM334
5/10
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相關(guān)代理商/技術(shù)參數(shù) |
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