LT1638CMS8 Linear Technology, LT1638CMS8 Datasheet - Page 13

• Manufacturer Part Number: LT1638CMS8
• Description: IC OPAMP R-R IN/OUT DUAL 8-MSOP
• Manufacturer: Linear Technology
• Series: Over-The-Top®r

Specifications of LT1638CMS8

• Amplifier Type: General Purpose
• Number Of Circuits: 2
• Output Type: Rail-to-Rail
• Slew Rate: 0.4 V/µs
• Gain Bandwidth Product: 1.2MHz
• Current - Input Bias: 20nA
• Voltage - Input Offset: 400µV
• Current - Supply: 205µA
• Current - Output / Channel: 40mA
• Voltage - Supply, Single/dual (±): 2.5 V ~ 44 V, ±1.25 V ~ 22 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• -3db Bandwidth: -

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
the op amp and could be as high as 44V.
SIMPLIFIED SCHEMATIC
Figure 3. Positive Supply Rail Current Sense
ONE AMPLIFIER
LOAD
+
R1
6k
V
+
10μA
0.2Ω
200Ω
200Ω
Q5
Q1
I
LOAD
Q4
V
+
OUT
, is not limited to the 5V supply of
–
–IN
+IN
+
1/2 LT1638
Q6
= (2Ω)(I
5V
R2
R3
1k
1k
LOAD
)
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 fi xed at 1.2V generating an output
current equal to 1.2V/R1.
Q13
R4
8k
Q14
R5
8k
LT1634-1.2
Q15
Figure 4. Current Source
D3
+
–
1/2 LT1638
Q16
Q3
V
CC
Q17
Q18
LT1638/LT1639
V
Q19
CC
R1
1638/39 F04
I
OUT
Q20
Q22
Q21
I
1638/39 SS
OUT
OUT
=
1.2V
R1
V
V
+
–
13
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