ADR445B(RevE) Просмотр технического описания (PDF) - Analog Devices

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ADR445B
(Rev.:RevE)

Ultralow Noise, LDO XFET Voltage References with Current Sink and Source

Analog Devices 

ADR440/ADR441/ADR443/ADR444/ADR445

APPLICATIONS INFORMATION

OUTPUT ADJUSTMENT

The ADR44x family features a TRIM pin that allows the user to

adjust the output voltage of the part over a limited range. This

allows errors from the reference and overall system errors to be

trimmed out by connecting a potentiometer between the output

and the ground, with the wiper connected to the TRIM pin.

Figure 35 shows the optimal trim configuration. R1 allows fine

adjustment of the output and is not always required. RP should

be sufficiently large so that the maximum output current from

the ADR44x is not exceeded.

0.1µF

2

VIN

VOUT 6

ADR440/

ADR441/

ADR443/

ADR444/

ADR445

TRIM 5

GND

4

0.1µF

VO = ±0.5%

R1

100kΩ

RP

10kΩ

R2

1kΩ

Figure 35. ADR44x Trim Function

Using the trim function has a negligible effect on the temperature

performance of the ADR44x. However, all resistors need to be

low temperature coefficient resistors, or errors may occur.

BIPOLAR OUTPUTS

By connecting the output of the ADR44x to the inverting ter-

minal of an operational amplifier, it is possible to obtain both

positive and negative reference voltages. Care must be taken

when choosing Resistors R1 and R2 (see Figure 36). These

resistors must be matched as closely as possible to ensure mini-

mal differences between the negative and positive outputs. In

addition, care must be taken to ensure performance over

temperature. Use low temperature coefficient resistors if the

circuit is used over temperature; otherwise, differences exist

between the two outputs.

+VDD

0.1µF

2

VIN

ADR440/

ADR441/

ADR443/

ADR444/

ADR445

VOUT 6

+5V

GND

0.1µF

R1

R2

10kΩ 10kΩ

4

+10V

–5V

R3

5kΩ

–10V

Figure 36. ADR44x Bipolar Outputs

PROGRAMMABLE VOLTAGE SOURCE

To obtain different voltages than those offered by the ADR44x,

some extra components are needed. In Figure 37, two potenti-

ometers are used to set the desired voltage and the buffering

amplifier provides current drive. The potentiometer connected

between VOUT and GND, with its wiper connected to the

noninverting input of the operational amplifier, takes care of

coarse trim. The second potentiometer, with its wiper connected

to the trim terminal of the ADR44x, is used for fine adjustment.

Resolution depends on the end-to-end resistance value and the

resolution of the selected potentiometer.

+VDD

2

VIN

ADR440/

ADR441/

ADR443/

ADR444/

ADR445

VOUT 6

GND

4

R1

R2

10kΩ 10kΩ

ADJ VREF

Figure 37. Programmable Voltage Source

For a completely programmable solution, replace the two

potentiometers in Figure 37 with one Analog Devices dual

digital potentiometer, offered with either an SPI or an I2C

interface. These interfaces set the position of the wiper on both

potentiometers and allow the output voltage to be set. Table 9

lists compatible Analog Devices digital potentiometers.

Rev. E | Page 15 of 20

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