ADR280 Analog Devices, Inc., ADR280 Datasheet - Page 7

• Manufacturer Part Number: ADR280
• Description: 1.2 V Ultralow Power High Psrr Voltage Reference
• Manufacturer: Analog Devices, Inc.

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
a proportional to absolute temperature (PTAT) voltage that
cancels the complementary to absolute temperature (CTAT) Q9
V
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.
BE
voltage. As a result, a core band gap voltage that is almost a
BE
produces
Rev. C | Page 7 of 12
R1
R3
Q17
Q1
Q3
R5
R7
PNP3
Q18
R6
R4
Q9
R8
R9
Figure 11. Simplified Architecture
I1
Q5
Q6
R2
Q2
R13
Q10
R12
R10
C1
R11
Q7
ADR280
V+
V
V–
OUT