ADR390ART-RL7 查看數據表（PDF） - Analog Devices

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ADR390ART-RL7

Precision Low Drift 2.048 V/2.5 V/4.096 V/5.0 V SOT-23 Reference with Shutdown

Analog Devices 

ADR390/ADR391/ADR392/ADR395

100

90

80

70

60

CL = 0␮F

50

40

30

20

CL = 0.1␮F

CL = 1␮F

10

0

10

100

1k

10k

100k

1M

FREQUENCY – Hz

TPC 37. Output Impedance vs. Frequency

THEORY OF OPERATION

Band gap references are the high performance solution for low

supply voltage and low power voltage reference applications, and

the ADR390/ADR391/ADR392/ADR395 is no exception. The

uniqueness of this product lies in its architecture. By observing

Figure 2, the ideal zero TC band gap voltage is referenced to the

output, not to ground. Therefore, if noise exists on the ground

line, it will be greatly attenuated on VOUT. The band gap cell

consists of the pnp pair Q51 and Q52, running at unequal cur-

rent densities. The difference in VBE results in a voltage with a

positive

TC,

which

is

amplified

by

the

ratio

of

2×

R58

. This

R54

PTAT voltage, combined with VBEs of Q51 and Q52, produces

the stable band gap voltage.

Reduction in the band gap curvature is performed by the ratio of

the resistors R44 and R59, one of which is linearly temperature

dependent. Precision laser trimming and other patented circuit

techniques are used to further enhance the drift performance.

VIN

Q1

R59

R44

VOUT (FORCE)

VOUT (SENSE)

R58

R49

R54

SHDN

R53

Q51

Q52

R48

R60

R61

GND

Figure 2. Simplified Schematic

Device Power Dissipation Considerations

The ADR390/ADR391/ADR392/ADR395 is capable of deliver-

ing load currents to 5 mA with an input voltage that ranges from

2.8 V (ADR391 only) to 15 V. When this device is used in applica-

tions with large input voltages, care should be taken to avoid

exceeding the specified maximum power dissipation or junction

temperature that could result in premature device failure. The

following formula should be used to calculate a device’s maxi-

mum junction temperature or dissipation:

PD

=

TJ − TA

θ JA

In this equation, TJ and TA are, respectively, the junction and

ambient temperatures, PD is the device power dissipation, and

␪JA is the device package thermal resistance.

Shutdown Mode Operation

The ADR390/ADR391/ADR392/ADR395 includes a shutdown

feature that is TTL/CMOS level compatible. A logic LOW or a

zero volt condition on the SHDN Pin is required to turn the device

off. During shutdown, the output of the reference becomes a

high impedance state where its potential would then be deter-

mined by external circuitry. If the shutdown feature is not used,

the SHDN Pin should be connected to VIN (Pin 2).

APPLICATIONS

BASIC VOLTAGE REFERENCE CONNECTION

The circuit in Figure 3 illustrates the basic configuration for the

ADR39x family. Decoupling capacitors are not required for circuit

stability. The ADR39x family is capable of driving capacitive

loads from 0 µF to 10 µF. However, a 0.1 µF ceramic output

capacitor is recommended to absorb and deliver the charge as is

required by a dynamic load.

SHUTDOWN

INPUT

*

CB 0.1␮F

SHDN

GND

ADR39x

VIN

VOUT(S) VOUT(F)

* NOT REQUIRED

OUTPUT

*

CB 0.1␮F

Figure 3. Basic Configuration for the ADR39x Family

Stacking Reference ICs for Arbitrary Outputs

Some applications may require two reference voltage sources,

which are a combined sum of standard outputs. Figure 4

circuit shows how this “stacked output” reference can be

implemented:

–12–

REV. C

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