LM334S8#PBF Linear Technology, LM334S8#PBF Datasheet - Page 5

• Manufacturer Part Number: LM334S8#PBF
• Description: IC CURRENT SOURCE 8SOIC
• Manufacturer: Linear Technology

Specifications of LM334S8#PBF

• Function: Current Source
• Voltage - Input: 0.8 ~ 40 V
• Current - Output: 10mA
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Accuracy: -
• Sensing Method: -

APPLICATIO S I FOR ATIO
Basic Theory of Operation
The equivalent circuit of the LM134 is shown in Figure 1.
A reference voltage of 64mV is applied to the minus input
of A1 with respect to the V
to keep the R pin at 64mV, independent of the value of
R
the current flowing out of the V
total current into the V
and is equal to:
The 67.7mV equivalent reference voltage is directly pro-
portional to absolute temperature in degrees Kelvin (see
curve, “Operating Current vs Temperature”). This means
that the reference voltage can be plotted as a straight line
going from 0mV at absolute zero temperature to 67.7mV
at 298 K (25 C). The slope of this line is 67.7mV/298 =
227 V/ C.
The accuracy of the device is specified as a percent error
at room temperature, or in the case of the -3 and -6
devices, as both a percent error and an equivalent tem-
perature error. The LM134 operating current changes at a
percent rate equal to (100)(227 V/ C)/(67.7mV) = 0.336%/
lent to 3 C temperature error when the device is used as
a temperature sensor. The slope accuracy (temperature
coefficient) of the LM134 is expressed as a ratio com-
pared to unity. The LM134-3, for instance, is specified at
0.98 to 1.02, indicating that the maximum slope error of
C at 25 C, so each 1% operating current error is equiva-
SET
64
. Transistor Q1 is matched to Q2 at a 17:1 ratio so that
R
SET
mV
Q1
17
18
U
67 7
+
R
pin. This total current is called I
.
SET
Figure 1.
mV
A1
U
–
pin. A1 serves the drive to Q2
+
–
64mV
–
pin is always 1/18 of the
V
W
Q2
+
+
–
I
SET
R
R
V
134 F01
SET
–
U
SET
the device is 2% when the room temperature current is
set to the exact desired value.
Supply Voltage Slew Rate
At slew rates above a given threshold (see curve), the
LM134 may exhibit nonlinear current shifts. The slewing
rate at which this occurs is directly proportional to I
I
the limits is 1V/ s. Slew rates above the limit do not harm
the LM134, or cause large currents to flow.
Thermal Effects
Internal heating can have a significant effect on current
regulation for I
1V increase across the LM134 at I
junction temperature by 0.4 C in still air. Output current
(I
change in current due to temperature rise will be (0.4)(0.33)
= 0.132%. This is a 10:1 degradation in regulation com-
pared to true electrical effects. Thermal effects, therefore,
must be taken into account when DC regulation is critical
and I
age or the TO-92 leads can reduce this effect by more than
3:1.
Shunt Capacitance
In certain applications, the 15pF shunt capacitance of the
LM134 may have to be reduced, either because of loading
problems or because it limits the AC output impedance of
the current source. This can be easily accomplished by
buffering the LM134 with a FET, as shown in the applica-
tions. This can reduce capacitance to less than 3pF and
improve regulation by at least an order of magnitude. DC
characteristics (with the exception of minimum input
voltage) are not affected.
Noise
Current noise generated by the LM134 is approximately 4
times the shot noise of a transistor. If the LM134 is used
as an active load for a transistor amplifier, input referred
noise will be increased by about 12dB. In many cases, this
is acceptable and a single stage amplifier can be built with
a voltage gain exceeding 2000.
SET
SET
= 10 A, maximum dv/dt is 0.01V/ s; at I
) has a temperature coefficient of 0.33%/ C, so the
SET
exceeds 100 A. Heat sinking of the TO-46 pack-
SET
greater than 100 A. For example, each
LM134 Series
SET
= 1mA will increase
SET
= 1mA,
SET
5
. At