Rainbow-electronics MAX1326 Uživatelský manuál stáhnout pdf (Strana 21)

MAX1316–MAX1318/MAX1320–MAX1322/MAX1324–MAX1326

8-/4-/2-Channel, 14-Bit, Simultaneous-Sampling ADCs

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

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The input range is centered about V

MSV

. Normally,

MSV = AGND, and the input is symmetrical about zero.

For a custom midscale voltage, drive MSV with an

external voltage source. Noise present on MSV directly

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

voltage reference with adequate bypassing to prevent

MSV from degrading ADC performance. For maximum

FSR, be careful not to violate the absolute maximum

voltage ratings of the analog inputs when choosing

MSV

. Determine the input voltage as a function of

REF

, V

MSV

, and the output code in decimal using the

following equation:

Unipolar 0 to +5V Devices

Table 7 and Figure 11 show the offset binary transfer

function for the MAX1316/MAX1317/MAX1318 with a 0

to +5V input range. The FSR is two times the voltage at

REF. The internal +2.500V reference gives a +5V FSR,

while an external +2V to +3V reference allows an FSR

of +4V to +6V, respectively. Calculate the LSB size

using the following equation:

This equals 0.3052mV when using the internal reference.

LSB

REF

×2

V LSB CODE V

CH MSV_

=× +

Figure 10. ±5V Bipolar Transfer Function

4 x V

REF

4 x V

REF

4 x V

REF

1 LSB =

TWO'S COMPLEMENT BINARY OUTPUT CODE

-8192 -8190 +8191+8189

0x2000

0x2001

0x2002

0x2003

0x1FFF

0x1FFE

0x1FFD

0x1FFC

0x3FFF

0x0000

0x0001

-1 0 +1

(MSV)

INPUT VOLTAGE (V

CH_

- V

MSV

IN LSBs)

Table 6. ±5V Bipolar Code Table

TWO’S COMPLEMENT

BINARY OUTPUT CODE

DECIMAL

EQUIVALENT

OUTPUT

(CODE

)

INPUT

VOLTAGE (V)

REF

= 2.5V,

MSV

= 0V)

01 1111 1111 1111

0x1FFF

8191

4.9997

±0.5 LSB

01 1111 1111 1110

0x1FFE

8190

4.9991

±0.5 LSB

00 0000 0000 0001

0x0001

0.0009

±0.5 LSB

00 0000 0000 0000

0x0000

0.0003

±0.5 LSB

11 1111 1111 1111

0x3FFF

-1

-0.0003

±0.5 LSB

10 0000 0000 0001

0x2001

-8191

-4.9991

±0.5 LSB

10 0000 0000 0000

0x2000

-8192

-4.9997

±0.5 LSB

Table 7. 0 to +5V Unipolar Code Table

BINARY OUTPUT CODE

DECIMAL

EQUIVALENT

OUTPUT

(CODE

)

INPUT

VOLTAGE (V)

REF

= V

REFMS

= 2.5V)

11 1111 1111 1111

0x3FFF

16383

4.9998

±0.5 LSB

11 1111 1111 1110

0x3FFE

16382

4.9995

±0.5 LSB

10 0000 0000 0001

0x2001

8193

2.5005

±0.5 LSB

10 0000 0000 0000

0x2000

8192

2.5002

±0.5 LSB

01 1111 1111 1111

0x1FFF

8191

2.4998

±0.5 LSB

00 0000 0000 0001

0x0001

0.0005

±0.5 LSB

00 0000 0000 0000

0x0000

0.0002

±0.5 LSB

1 2 ... 16 17 18 19 20 21 22 23 24 25 26 27

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