SPT7722 Ver la hoja de datos (PDF) - Fairchild Semiconductor

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componentes Descripción

Fabricante

SPT7722

8-bit, 250 MSPS A/D Converter with Demuxed Outputs

Fairchild Semiconductor 

SPT7722

Mode

Select

Reset

Diff In

Clock Power

Diff Down

30kΩ

DATA SHEET

+D3/5

AIN

T1

VCM

DA0–DA7

VIN+

50Ω

SPT7722

DCLKOUT

DCLKOUT

VIN–

Mini-Circuit

T1-6T

.01µF

DB0–DB7

Interfacing

Logics

Notes:

.01µF

.01µF

1) FB = Ferrite bead. It must placed as close to the ADC as possible.

2) All 0.01 microfarad capacitors are surface mount caps. They must be

placed as close to the respective pin as possible.

+

3) For details, refer to the Application Note AN7722.

+

FB

10µF

10µF

+A5

+D3/5

Figure 3. Typical Interface Circuit

+D3/5

AVCC

CLK

&

RES

300Ω

100kΩ

17.5kΩ

300Ω

7.5kΩ

CLK

&

RES

AGND

Figure 4. CLK and Reset Equivalent Circuit

(without ESD Diodes)

100kΩ

AVCC

100kΩ

VIN+

300Ω

200Ω

200Ω

300Ω

VIN–

100kΩ

100kΩ

AGND

Typical Interface Circuit

Very few external components are required to achieve the

stated device performance. Figure 3 shows the typical inter-

face requirements when using the SPT7722 in normal circuit

operation. The following sections provide descriptions of the

major functions and outline performance criteria to consider

for achieving the optimal device performance.

Analog Input

The input of the SPT7722 can be configured in various ways

depending on whether a single-ended or differential input is

desired.

The AC-coupled input is most conveniently implemented

using a transformer with a center-tapped secondary winding.

The center tap is connected to the VCM pin as shown in

Figure 3. To obtain low distortion, it is important that the

selected transformer does not exhibit core saturation at the

full-scale voltage. Proper termination of the input is important

for input signal purity. A small capacitor across the input

attenuates kickback noise from the internal track-and-hold.

Figure 6 illustrates a solution (based on operational amplifiers)

that can be used if a DC-coupled single-ended input is

desired.

Figure 5. Analog Input Equivalent Circuit

Rev. 1.0.2 December 2002

9

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