LT1638 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
LT1638
Linear Technology
'LT1638' PDF : 18 Pages View PDF
LT1638/LT1639
TYPICAL APPLICATIONS
The application in Figure 3 utilizes the Over-The-Top
capabilities of the LT1638. The 0.2Ω resistor senses the
load current while the op amp and NPN transistor form a
closed loop making the collector current of Q1
proportional to the load current. As a convenient monitor,
the 2k load resistor converts the current into a voltage. The
positive supply rail, V+, is not limited to the 5V supply of
the op amp and could be as high as 44V.
The Figure 4 application uses the LT1638 in conjunction
with the LT1634 micropower shunt reference. The supply
current of the op amp also biases the reference. The drop
across resistor R1 is fixed at 1.2V generating an output
current equal to 1.2V/R1.
V+
200Ω
5V
0.2Ω
200Ω
LOAD ILOAD
+
1/2 LT1638
–
VOUT = (2Ω)(ILOAD)
Q1
2N3904
0V TO 4.3V
2k
1638/39 F03
Figure 3. Positive Supply Rail Current Sense
VCC
LT1634-1.2
VCC
R1
+
1/2 LT1638
–
IOUT
=
1.2V
R1
IOUT
1638/39 F04
Figure 4. Current Source
SIMPLIFIED SCHEMATIC
Q1
R1
6k
Q4
+
10μA
R2
1k
–IN
R3
1k
+IN
Q2
D1
D2
Q7 Q8
Q11 Q12
Q9
Q10
Q13
Q3
D3
V+
Q22
Q15
Q14
Q19
Q17
Q16 Q18
Q20
OUT
Q21
Q5
Q6
ONE AMPLIFIER
D4 D5
R4
R5
8k
8k
V–
1638/39 SS
16389fg
13
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