Rainbow-electronics MAX1209 Manual de usuario descargar pdf (Pagina 15)

REFOUT sources up to 1.0mA and sinks up to 0.1mA

for external circuits with a load regulation of 35mV/mA.

Short-circuit protection limits I

REFOUT

to a 2.1mA

source current when shorted to GND and a 0.24mA

sink current when shorted to V

Analog Inputs and Reference

Configurations

The MAX1209 full-scale analog input range is

adjustable from ±0.35V to ±1.15V with a common-

mode input range of V

/ 2 ±0.5V. The MAX1209 pro-

vides three modes of reference operation. The voltage

at REFIN (V

REFIN

) sets the reference operation mode

(Table 1).

To operate the MAX1209 with the internal reference,

connect REFOUT to REFIN either with a direct short or

through a resistive divider. In this mode, COM, REFP,

and REFN are low-impedance outputs with V

COM

/ 2, V

REFP

= V

/ 2 + V

REFIN

/ 4, and V

REFN

/ 2 - V

REFIN

/ 4. The REFIN input impedance is very

large (>50MΩ). When driving REFIN through a resistive

divider, use resistances ≥10kΩ to avoid loading

REFOUT.

Buffered external reference mode is virtually identical to

internal reference mode except that the reference source

is derived from an external reference and not the

MAX1209 REFOUT. In buffered external reference mode,

apply a stable 0.7V to 2.3V source at REFIN. In this

mode, COM, REFP, and REFN are low-impedance out-

puts with V

COM

= V

/ 2, V

REFP

= V

/ 2 + V

REFIN

/ 4,

and V

REFN

= V

/ 2 - V

REFIN

/ 4.

To operate the MAX1209 in unbuffered external refer-

ence mode, connect REFIN to GND. Connecting REFIN

to GND deactivates the on-chip reference buffers for

COM, REFP, and REFN. With the respective buffers

deactivated, COM, REFP, and REFN become high-

impedance inputs and must be driven through sepa-

rate, external reference sources. Drive V

COM

to V

/ 2

±5%, and drive REFP and REFN such that V

COM

REFP

+ V

REFN

) / 2. The full-scale analog input range

is ±(V

REFP

- V

REFN

MAX1209

12-Bit, 80Msps, 3.3V IF-Sampling ADC

______________________________________________________________________________________ 15

T/H

CLKN

CLKP

TRACK HOLDTRACK HOLDTRACK HOLDTRACKHOLD

ANALOG

INPUT

SAMPLED

DATA

Figure 4. T/H Aperture Timing

REFIN

REFERENCE MODE

35% V

REFOUT

to 100%

REFOUT

Internal Reference Mode. Drive REFIN with REFOUT either through a direct short or a resistive divider.

The full-scale analog input range is ±V

REFIN

/ 2:

COM

= V

/ 2

REFP

= V

/ 2 + V

REFIN

/ 4

REFN

= V

/ 2 – V

REFIN

/ 4

0.7V to 2.3V

Buffered External Reference Mode. Apply an external 0.7V to 2.3V reference voltage to REFIN.

The full-scale analog input range is ±V

REFIN

/ 2:

COM

= V

/ 2

REFP

= V

/ 2 + V

REFIN

/ 4

REFN

= V

/ 2 – V

REFIN

/ 4

<0.4V

Unbuffered External Reference Mode. Drive REFP, REFN, and COM with external reference sources.

The full-scale analog input range is ±(V

REFP

– V

REFN

Table 1. Reference Modes

1 2 ... 10 11 12 13 14 15 16 17 18 19 20 ... 26 27

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Rainbow-electronics MAX1209 Manual de usuario Pagina 15

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