Rainbow-electronics MAX1314 Manual de usuario descargar pdf (Pagina 27)

MAX1304–MAX1306/MAX1308–MAX1310/MAX1312–MAX1314

8-/4-/2-Channel, 12-Bit, Simultaneous-Sampling ADCs

with ±10V, ±5V, and 0 to +5V Analog Input Ranges

______________________________________________________________________________________ 27

Transfer Functions

Unipolar 0 to +5V Devices

Table 5 and Figure 12 show the offset binary transfer

function for the MAX1304/MAX1305/MAX1306 with a 0

to +5V input range. The full-scale input range (FSR) is

two times the voltage at REF. The internal +2.5V refer-

ence gives a +5V FSR, while an external +2V to +3V

reference allows an FSR of +4V to +6V, respectively.

Calculate the LSB size using:

which equals 1.22mV when using a 2.5V reference.

The input range is centered about V

MSV

, internally set

to +2.5V. For a custom midscale voltage, drive REF

with an external voltage source and MSV will follow

REF

. Noise present on MSV or REF

directly cou-

ples into the ADC result. Use a precision, low-drift volt-

age reference with adequate bypassing to prevent MSV

from degrading ADC performance. For maximum FSR,

do not violate the absolute maximum voltage ratings of

the analog inputs when choosing MSV.

Determine the input voltage as a function of V

REF

MSV

, and the output code in decimal using:

CH_

= LSB x CODE

+ V

MSV

- 2.500V

LSB

REF

Table 5. 0 to 5V Unipolar Code Table

BINARY

DIGITAL

OUTPUT CODE

DECIMAL

EQUIVALENT

DIGITAL OUTPUT

CODE

(CODE

)

INPUT VOLTAGE

(V)

REF

= +2.5V

REFMS

= +2.5V

1111 1111 1111

= 0xFFF

4095

+4.9994 ± 0.5 LSB

1111 1111 1110

= 0xFFE

4094

+4.9982 ± 0.5 LSB

1000 0000 0001

= 0x801

2049

+2.5018 ± 0.5 LSB

1000 0000 0000

= 0x800

2048

+2.5006 ± 0.5 LSB

0111 1111 1111

= 0x7FF

2047

+2.4994 ± 0.5 LSB

0000 0000 0001

= 0x001

+0.0018 ± 0.5 LSB

0000 0000 0000

= 0x000

+0.0006 ± 0.5 LSB

(

)

2 x V

REF

2 x V

REF

1 LSB =

BINARY OUTPUT CODE

021

40954093

0x0000

0x0001

0x0002

0x0003

0xFFF

0xFFE

0xFFD

0xFFC

0x7FF

0x800

0x801

2046 2048

2050

(MSV)

INPUT VOLTAGE (LSBs)

Figure 12. 0 to +5V Unipolar Transfer Function

1 2 ... 22 23 24 25 26 27 28 29 30 31 32 ... 35 36

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Rainbow-electronics MAX1314 Manual de usuario Pagina 27

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