ADR550ART-REEL7(RevA) データシートの表示（PDF） - Analog Devices

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ADR550ART-REEL7
(Rev.:RevA)

High Precision Shunt Mode Voltage References

Analog Devices 

ADR520/ADR525/ADR530/ADR540/ADR550

THEORY OF OPERATION

The ADR520/ADR525/ADR530/ADR540/ADR550 use the

band gap concept to produce a stable, low temperature

coefficient voltage reference suitable for high accuracy data

acquisition components and systems. The devices use the

physical nature of a silicon transistor base-emitter voltage in the

forward-biased operating region. All such transistors have

approximately a –2 mV/°C temperature coefficient (TC),

making them unsuitable for direct use as a low temperature

coefficient reference. Extrapolation of the temperature

characteristic of any one of these devices to absolute zero (with

the collector current proportional to the absolute temperature),

however, reveals that its VBE approaches approximately the

silicon band gap voltage. Thus, if a voltage develops with an

opposing temperature coefficient to sum the VBE, a zero

temperature coefficient reference results. The ADR5xx circuit

shown in Figure 18 provides such a compensating voltage (V1)

by driving two transistors at different current densities and

amplifying the resultant VBE difference (∆VBE, which has a

positive temperature coefficient). The sum of VBE and V1

provides a stable voltage reference over temperature.

+

V+

V1

• The RBIAS must be large enough so that IIN does not exceed

10 mA when the supply voltage is at its maximum value

and the load current is at its minimum value.

Given these conditions, the RBIAS is determined by the supply

voltage (VCC), the ADR5xx load and operating current (IL and

IQ), and the ADR5xx output voltage (VOUT).

RBIAS

=

VCC

IL

− VOUT

− IIN

(3)

VS

RBIAS

IIN

IIN + IL

VOUT

IL

ADR550

Figure 19. Shunt Reference

Precision Negative Voltage Reference

The ADR5xx is suitable for applications where a precise

negative voltage is desired. Figure 20 shows the ADR5xx

configured to provide a negative output.

–

+

∆VBE

–

+

VBE

–

V–

Figure 18. Circuit Schematic

APPLICATIONS

The ADR520/ADR525/ADR530/ADR540/ADR550 are a series

of precision shunt voltage references. They are designed to

operate without an external capacitor between the positive and

negative terminals. If a bypass capacitor is used to filter the

supply, the references remains stable.

All shunt voltage references require an external bias resistor

(RBIAS) between the supply voltage and the reference (see

Figure 19). The RBIAS sets the current that flows through the load

(IL) and the reference (IIN). Because the load and the supply

voltage can vary, the RBIAS needs to be chosen based on the

following considerations:

• The RBIAS must be small enough to supply the minimum IIN

current to the ADR5xx, even when the supply voltage is at

its minimum value and the load current is at its maximum

value.

ADR525

RBIAS

–2.5V

VCC

Figure 20. Negative Precision Reference Configuration

Output Voltage Trim

The ADR5xx TRIM terminal can be used to adjust the output

voltage over a range of ±0.5%. This allows systems designers to

trim system errors by setting the reference to a voltage other

than the preset output voltage. An external mechanical or elec-

trical potentiometer can be used for this adjustment. Figure 21

illustrates how the output voltage can be trimmed by using the

AD5273, an Analog Devices 10 kΩ potentiometer.

VCC

RBIAS

ADR530

R1

470kΩ

VOUT

AD5273

POTENTIOMETER

10kΩ

Figure 21. Output Voltage Trim

Rev. A | Page 11 of 16

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