ADR280

Rev. C | Page 7 of 12

THEORY OF OPERATION

The ADR280 provides the basic core 1.2 V band gap reference.

It contains two NPN transistors, Q9 and Q17, with their emitter

a proportional to absolute temperature (PTAT) voltage that

cancels the complementary to absolute temperature (CTAT) Q9

constant 1.2 V over temperature is generated (see Figure 11).

Precision laser trimming of the internal resistors and other

proprietary circuit techniques are used to enhance the initial

accuracy, temperature curvature, and temperature drift

performance.

R1

R3

R5

R7

R9

Q17

Q9

Q18

R8

Q3

R6

Q5

Q6

R4

Q1

PNP3

R2

R12

Q2

Q10

R13

C1

Q7

R10

R11

V–

V+

I1

Figure 11. Simplified Architecture