Rainbow-electronics MAX1208 Bedienungsanleitung PDF herunterladen (Seite 23)

Unbuffered External

Reference Drives Multiple ADCs

The unbuffered external reference mode allows for pre-

cise control over the MAX1208 reference and allows

multiple converters to use a common reference.

Connecting REFIN to GND disables the internal refer-

ence, and allows REFP, REFN, and COM to be driven

directly by a set of external reference sources.

Figure 14 uses the MAX6029EUK30 precision 3.000V

reference as a common reference for multiple convert-

ers. A five-component resistive divider chain follows the

MAX6029 voltage reference. The 0.47µF capacitor along

this chain creates a 10Hz lowpass filter. Three MAX4230

operational amplifiers buffer taps along this resistor

chain providing 2.157V, 1.649V, and 1.141V to the

MAX1208’s REFP, COM, and REFN reference inputs,

MAX1208

12-Bit, 80Msps, 3.3V ADC

______________________________________________________________________________________ 23

MAX1208

*PLACE THE 1

F REFP-TO-REFN BYPASS CAPACITOR AS CLOSE TO THE DEVICE AS POSSIBLE.

0.1

2.157V

+3.3V

Ω

1.47k

Ω

+3.3V

330

+3.3V

2.2

0.1

REFOUT

REFN

REFIN

GND

COM

REFP

MAX6029EUK30

MAX4230

0.1

0.47

1.649V

Ω

1.47k

Ω

+3.3V

330

MAX4230

0.1

1.141V

Ω

1.47k

Ω

+3.3V

330

MAX4230

MAX1208

+3.3V

2.2

0.1

REFOUT

REFN

REFIN

GND

COM

REFP

3.000V

24.3k

Ω

20k

Ω

26.7k

Ω

26.7k

Ω

20k

Ω

20k

Ω

20k

Ω

0.1

2.2

Figure 14. External Unbuffered Reference Driving Multiple ADCs

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

12-Bit, 80Msps, 3.3V ADC 1

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