CS5516-ASZ datasheet(34/41 Pages) CIRRUS

34 / 41 page

posed of one byte for command which is trans-

mitted with its LSB first.

The command is

followed by three data bytes which make up the

24-bit word to be written to the selected register

of the A/D converter. The three bytes are trans-

mitted lowest order byte first (bits 7 - 0) with the

LSB of the byte transmitted first.

Figure 3 illustrates the power supply connections

to the evaluation board. Voltages of +5 and -5

analog and +5 digital are required.

Using the Evaluation Board

Prior to using the board to evaluate the CS5516

or CS5520 A/D converter, a good understanding

of the full potential of the converter is necessary.

It is recommended that the CS5516/CS5520 de-

vice data sheet be thoroughly read prior to

attemp ting to u se the ev al uation board.

The CS5516 or CS5520 bridge transducer A/D

converter actually contains two A/D converters.

One of the converters is used to convert the

VREF voltage input, and the other is used to

convert the AIN signal input.

Both converters

utilize an on-chip voltage reference to perform

conversions of their respective inputs.

Since

both converters use the same reference they

track one another. The digital processing logic

of the A/D converter depends on the presence of

both signals to properly compute a digital output

word. If the evaluation board is configured for

bridge measurement, and no bridge (load cell or

simulator) is connected to the bridge transducer

terminal block, the converter will output a code

of zero because no reference voltage is present

between the VREF+ and VREF- pins.

The span of the AIN input signal is determined

by a combination of the instrumentation ampli-

fier gain (X25), the programmable gain amplifier

(PGA) gain, the magnitude of the voltage be-

tween the VREF+ and VREF- input pins, and

the calibration words for gain and offset. For ex-

Read

Write

Conversion Data Register

50(H)

Configuration Register

51(H)

D1(H)

DAC Register

53(H)

D3(H)

Gain Register

52(H)

D2(H)

AIN Ratiometric Offset Register

54(H)

D4(H)

AIN Nonratiometric Offset Register

55(H)

D5(H)

VREF Nonratiometric Offset Register

56(H)

D6(H)

Table 1. Microcontroller commands via RS-232

+5VD

0.1

µF

+5VA

0.1

µF

0.1

µF

-5VA

-5V

+5V

AGND

DGND

Figure 3. Power Supplies

CDB5516/CDB5520

DS74DB3

DS74DB4

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