5

LT1166

Overvoltage Protection

diodes that turn on when they exceed

±12V. These diodes

act as ESD protection and serve to protect the LT1166

when used with large power MOS devices that produce

limited to

±75mA maximum.

Multiplier Operation

Figure 2 shows the current multiplier circuit internal to the

LT1166 and how it works in conjunction with power

(bottom) of the LT1166 are set by the required “on”

base of Q9 and Q10 which are 1/10 the emitter area of Q7

and Q8. The expression for this current multiplier is:

or in terms of current:

mirrored and set the voltage on the (+) inputs of a pair of

internal op amps. The feedback of the op amps force the

same voltage on the (–) inputs and these voltages then

appear on the sense resistors in series with the power

devices. The product of the two currents in the power

devices is constant, as one increases the other decreases.

The excellent logging nature of Q9 and Q10 allows this

relation to hold over many decades in current.

and a small error current from the shunt regulator. During

high output current conditions the error current from the

regulator decreases. Current conducted by the regulator

needed to drive the power devices.

Driving the Input Stage

Figure 3 shows the input transconductance stage of the

input current is then mirrored by Q3/Q4 and current

supplied to Q4’s collector is sourced by power device M1.

The signal current in Q4’s emitter is absorbed by external

Figure 2. Constant Product Generator

+

–

1k

1k

1

Ω

1

Ω

8

1

3

5

4

Q7

× 10

Q8

× 10

Q9

× 1

Q10

× 1

1k

1k

–

+

10

SHUNT

REGULATOR

1166 • F02

1

Ω

1

Ω

R1

R2

1

3

4

Q11

Q12

Q1

Q2

1k

1k

1166 • F03

Q4

× 32

Q6

× 32

Q3

× 1

Q5

× 1

2

Figure 3. Input Stage Driving Gates