AD1580BRT 查看數據表（PDF） - Analog Devices

零件编号

产品描述 (功能)

生产厂家

AD1580BRT

1.2 V Micropower, Precision Shunt Voltage Reference

Analog Devices 

AD1580

THEORY OF OPERATION

The AD1580 uses the “bandgap” concept to produce a stable,

low temperature coefficient voltage reference suitable for high

accuracy data acquisition components and systems. The device

makes use of the underlying 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, unsuitable for use directly as a low TC

reference; however, extrapolation of the temperature characteristic

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

current proportional to absolute temperature) reveals that its

VBE will go to approximately the silicon bandgap voltage. Thus,

if a voltage could be developed with an opposing temperature

coefficient to sum with VBE, a zero TC reference would result.

The AD1580 circuit in Figure 6, 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 TC). The sum of VBE and V1 provide a

stable voltage reference.

V+

V1

∆VBE

VBE

V–

Figure 6. Schematic Diagram

APPLYING THE AD1580

The AD1580 is simple to use in virtually all applications. To

operate the AD1580 as a conventional shunt regulator (Figure

7a), an external series resistor is connected between the supply

voltage and the AD1580. For a given supply voltage the series

resistor, RS, determines the reverse current flowing through the

AD1580. The value of RS must be chosen to accommodate the

expected variations of the supply voltage, VS, load current, IL,

and the AD1580 reverse voltage, VR, while maintaining an

acceptable reverse current, IR, through the AD1580.

The minimum value for RS should be chosen when VS is at

its minimum, and IL and VR are at their maximum while

maintaining the minimum acceptable reverse current.

The value of RS should be large enough to limit IR to 10 mA

when VS is at its maximum, and IL and VR are at their minimum.

The equation for selecting RS is as follows:

RS = (VS – VR)/(IR + IL)

Figure 7b shows a typical connection with the AD1580BRT

operating at a minimum of 100 µA that can provide ± 1 mA to

its load, while accommodating ± 10% power supply variations.

VS

RS

VR

IR

IR + IL

IL

VOUT

+5V(+3V) ±10%

RS

2.94kΩ

(1.30kΩ)

VR

VOUT

(a)

(b)

Figure 7. Typical Connection Diagram

TEMPERATURE PERFORMANCE

The AD1580 is designed for reference applications where

stable temperature performance is important. Extensive

temperature testing and characterization ensures that the device’s

performance is maintained over the specified temperature range.

Some confusion exists in the area of defining and specifying

reference voltage error over temperature. Historically, references

have been characterized using a maximum deviation per degree

centigrade, i.e., 50 ppm/°C. However, because of nonlinearities

in temperature characteristics which originated in standard

Zener references (such as “S” type characteristics), most

manufacturers now use a maximum limit error band approach

to specify devices. This technique involves the measurement of

the output at three or more different temperatures to guarantee

that the voltage will fall within the given error band. The

proprietary curvature correction design techniques used to

minimize the AD1580 nonlinearities allow the temperature

performance to be guaranteed using the maximum deviation

method. This method is of more use to a designer than the one

which simply guarantees the maximum error band over the

entire temperature change.

Figure 8 shows a typical output voltage drift for the AD1580

and illustrates the methodology. The maximum slope of the

two diagonals drawn from the initial output value at 25°C to the

output values at 85°C and –40°C determines the performance

grade of the device. For a given grade of the AD1580 the

designer can easily determine the maximum total error from the

initial tolerance plus temperature variation. For example, the

AD1580BRT initial tolerance is ± 1 mV, a ± 50 ppm/°C

temperature coefficient corresponds to an error band of ± 4 mV

1.2258

1.2256

1.2254

SLOPE = TC = —————(V—MA—X—– —VO—) —––––

(85°C – 25°C) x 1.225 x 10–6

VMAX

1.2252

1.2250

VO

1.2248

1.2246

1.2244

1.2242

1.2240

1.2238

–55

SLOPE = TC = —————(V—MI—N —– V—O—) —–––––

(–40°C – 25°C) x 1.225 x 10–6

VMIN

–35 –15

5 25 45 65

TEMPERATURE – °C

85 105 125

Figure 8. Output Voltage vs. Temperature

–4–

REV. 0

Share Link: