ADR380/ADR381

Rev. C | Page 11 of 16

THEORY OF OPERATION

Band gap references are the high performance solution for low

supply voltage and low power voltage reference applications, and

the ADR380/ADR381 are no exception. However, the uniqueness

of this product lies in its architecture. As shown in Figure 26,

the ideal zero TC band gap voltage is referenced to the output,

not to ground. The band gap cell consists of the PNP pair Q51

and Q52, running at unequal current densities. The difference

by the ratio of 2 × R58/R54. This PTAT voltage, combined with

Reduction in the band gap curvature is performed by the ratio

of the two resistors, R44 and R59. Precision laser trimming and

other patented circuit techniques are used to further enhance

the drift performance.

GND

Q1

R59

R54

Q51

R60

R61

R48

R49

R44

R58

R53

Q52

–

+

Figure 26. Simplified Schematic

DEVICE POWER DISSIPATION CONSIDERATIONS

The ADR380/ADR381 are capable of delivering load currents to

5 mA with an input voltage that ranges from 2.8 V (ADR381 only)

to 15 V. When this device is used in applications with large input

voltages, take care to avoid exceeding the specified maximum

power dissipation or junction temperature that may result in

premature device failure. Use the following formula to calculate

a device’s maximum junction temperature or dissipation:

JA

A

J

D

T

T

P

θ

−

=

where:

INPUT CAPACITOR

An input capacitor is not required on the ADR380/ADR381.

There is no limit for the value of the capacitor used on the input,

but a capacitor on the input improves transient response in

applications where the load current suddenly increases.

OUTPUT CAPACITOR

The ADR380/ADR381 do not need an output capacitor for

stability under any load condition. Using an output capacitor,

typically 0.1 μF, removes any very low level noise voltage and does

not affect the operation of the part. The only parameter that

degrades by applying an output capacitor is turn-on time. (This

varies depending on the size of the capacitor.) Load transient

response is also improved with an output capacitor, which acts

as a source of stored energy for a sudden increase in load current.