Datasheet

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
areas scaled in a fixed ratio. The difference in the V
BE
produces
a proportional to absolute temperature (PTAT) voltage that
cancels the complementary to absolute temperature (CTAT) Q9
V
BE
voltage. As a result, a core band gap voltage that is almost a
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
V
OUT
03065-013
Figure 11. Simplified Architecture