LT1638CS8 datasheet(12/16 Pages) LINER

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LT1638/LT1639

16389fd

TYPICAL APPLICATIONS

–

1/2 LT1638

V +

200

0.2

0V TO 4.3V

1638/39 F03

VOUT = (2Ω)(ILOAD)

2N3904

LOAD

ILOAD

Figure 4. Current Source

Figure 3. Positive Supply Rail Current Sense

SI PLIFIED SCHE ATIC

Q10

–IN

+IN

Q11

Q12

ONE AMPLIFIER

Q13

Q14

μA

Q15

Q19

Q16

Q18

Q22

V +

Q17

Q20

Q21

OUT

V –

1638/39 SS

–

1/2 LT1638

1.2V

IOUT =

LT1634-1.2

IOUT

1638/39 F04

VCC

The application in Figure 3 utilizes the Over-The-Top

capabilities of the LT1638. The 0.2

Ω 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.

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