lt1638is8-trpbf Linear Technology Corporation, lt1638is8-trpbf Datasheet - Page 12

• Manufacturer Part Number: lt1638is8-trpbf
• Description: Lt1639 -output Op Amps
• Manufacturer: Linear Technology Corporation

LT1638/LT1639
TYPICAL APPLICATIONS
SI PLIFIED SCHE ATIC
12
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
the op amp and could be as high as 44V.
W
Figure 3. Positive Supply Rail Current Sense
LOAD
ONE AMPLIFIER
V
+
+
R1
6k
0.2Ω
10μA
200Ω
200Ω
I
Q5
LOAD
Q1
Q4
V
+
OUT
+
–
, is not limited to the 5V supply of
1/2 LT1638
– IN
+IN
= (2Ω)(I
Q6
5V
R2
R3
W
1k
1k
LOAD
)
U
D4
Q1
2N3904
2k
1638/39 F03
D5
Q9
0V TO 4.3V
Q7
D1
Q8
Q10
D2
Q11
Q2
Q12
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.
Q13
R4
8k
Q14
R5
8k
LT1634-1.2
Figure 4. Current Source
Q15
D3
+
–
1/2 LT1638
V
CC
Q3
Q16
Q17
Q18
V
CC
Q19
R1
1638/39 F04
I
OUT
Q20
Q22
Q21
I
OUT
1638/39 SS
OUT
=
1.2V
R1
V
V
+
–
16389fd