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PDF AN629 Data sheet ( Hoja de datos )
| Número de pieza | AN629 | |
| Descripción | Digitally Adjustable Voltage References | |
| Fabricantes | Maxim Integrated Products | |
| Logotipo |  |
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DIGITAL POTENTIOMETERS
Jul 01, 2001
Digitally Adjustable Voltage References
A digitally adjustable voltage reference is useful in many applications. For instance, it can be
used to finely tune the reference voltage when absolute accuracy is required or to adjust the
reference voltage to match the full-scale voltage range of an analog-input signal to maximize the
dynamic range of an analog-to-digital conversion. You can easily create one by combining an
adjustable voltage reference with a digital potentiometer (pot). Using the digitally variable aspect
of the digital pot to control the adjustment voltage on the reference results in a flexible and
useful circuit. Three basic circuit topologies are presented here. The first achieves a coarse
adjustment over a wide voltage range, the second a fine adjustment over a narrow voltage
range, and the third a fine adjustment over a wide voltage range. These simple circuits can be
used directly or can form the basis for more complex control systems.
The output voltage of an adjustable voltage reference, like the MAX6160, is set by the ratio of
two resistors, R1 and R2, in Figure 1. The relationship between the voltage and the resistors is
given by the equation next to the circuit in the figure. The equations for calculating the values for
R1 and R2 are also shown.
Figure 1. The MAX6160 adjustable output circuit with fixed precision resistors
Coarse Adjustment over a Wide Voltage Range
Figure 2 combines the MAX6160 with the MAX5462 (a 100-kilohm, 32-tap digital pot). This
circuit is capable of digitally adjusting the output over the range from 1.23V to 5.3V. The ADJ pin
voltage limits the minimum output voltage, and the supply voltage for the MAX5462 and the
1 page  
Figure 6. Plot of Figure 5 circuit of reference voltage output versus pot A and pot B (32-by-32
taps used instead of 256-by-256 taps for clarity)
Summary
Three circuit topologies were presented that provide the capability to digitally adjust the
MAX6160's output voltage. The first topology provides the capability to coarsely adjust the
output voltage over a wide range using a 32- or 256-tap digital pot. The second topology is
capable of finely adjusting the output voltage about a single output voltage by using two fixed
resistors and a 32-tap digital pot. The third topology can finely tune the output voltage over a
wide range by using a dual, 256-tap digital pot. Table 2 summarizes the initial accuracy for each
circuit presented.
Table 2. Summary of Initial Accuracy
Output
Voltage
2.048V
2.500V
4.096V
MAX5462
32T, 100
Kilohms
5%
7%
11%
Digital Pot Features
MAX5401
256T, 100
Kilohms
MAX5160
32T, 50
Kilohms,
Two
Resistors
0.6%
0.5%
0.8%
0.5%
1.3%
0.5%
MAX5415
256T, 100
Kilohms,
Dual
0.06%
0.03%
0.08%
5 Page | ||
| Páginas | Total 6 Páginas | |
| PDF Descargar | [ Datasheet AN629.PDF ] | |
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