CDB5521 datasheet(8/28 Pages) CIRRUS

8 / 28 page

CDB5521/22/23/24/28

DS317DB2

1.3 Using the Evaluation Board

The CS5521/22/23/24/28 are highly integrated

ADCs. They contain a multiplexer, an instrumenta-

tion amplifier (IA), a programmable gain amplifier

(PGA), an on-chip charge pump drive (CPD), and

programmable output word rates (OWR). The IA

provides a set gain of 20 while the PGA sets the in-

put levels of the ADC at either 25 mV, 55 mV,

100 mV, 1 V, 2.5 V, or 5 V (for VREF = 2.5 V).

The CPD provides a square wave output. This out-

put, along with two diodes and two capacitors, is

used to supply the negative supply to the IA, en-

abling measurements of ground referenced signals.

The ADC’s digital filter allows the user to select

output word rates (OWR’s) from 1.88 Hz up to

101 Hz. higher output word rates can be attained

when a faster clock source is used. Since the

CS5521/22/23/24/28 have such a high degree of in-

tegration

and

flexibility,

the

CS5521/23

CS5522/24/28 data sheet should be read thorough-

ly before and consulted during the use of the

CDB5521/22/23/24/28. Table 1 lists the different

headers on the CDB5521/22/23/24/28 and their

functions. The locations of these headers are

marked on the top of the board, and the silkscreen

and layout of the board can also be found at the end

of this document in Figures 12, 13, and 14 for ref-

erence.

1.4.

Power Connections

Figure 4 illustrates the power supply connections to

the evaluation board. The +5 V Analog supplies the

analog section of the evaluation board, the LT1019

and the ADC. The -5 V Analog supplies the nega-

tive bias voltage circuitry. The +5 V Digital sup-

plies a separate five volts to the digital section of

the evaluation board, the 80C51, the reset circuitry,

and the RS-232 interface circuitry.

1.5 Negative Bias Voltage

The evaluation board provides three means of sup-

plying the Negative Bias Voltage (NBV). HDR4

(Header 4) selects between them. When HRD4 is in

position one, the LM337 supplies NBV with an ad-

justable voltage. R16 is used to adjust this voltage

between -1.25 V and -5 V. When in position two,

HDR4 grounds NBV. And by setting HDR4 to po-

sition three, the converter’s Charge Pump Drive

provides NBV with a dc rectified voltage, nominal-

ly -2.1 V.

Note:

NBV should not exceed a voltage more

negative than -3.0 V.

+5V Analog

-5V Analog

P6KE6V8P

47µF

C13

0.1µF

P6KE6V8P

47µF

C10

0.1µF

+5V Digital

P6KE6V8P

47µF

C12

0.1µF

+5V Analog

-5V Analog

+5V Digital

AGND

DGND

Figure 4. Power Supplies

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