CS5126 datasheet(22/32 Pages) CIRRUS

22 / 32 page

Power Supplies

Figure 1 shows the power supply arrangements.

The analog section of the board is powered by

± 15 volts, which is regulated down to ± 5 V for

the ADC. A separate +5 V digital supply is re-

quired to power the discrete logic. Be sure to

switch on the

± 15 V at the same time as, or be-

fore, the + 5 V logic supply. This will make sure

that the CLK and other logic signal are not driv-

ing the part before it is powered.

Analog Input

The analog input range is either

± Vref in the bi-

polar mode or 0 V to +Vref in the unipolar mode.

The voltage reference is factory set to the recom-

mended value of +4.5 volts, so the typical input

signal ranges become

± 4.5 volts or 0 V to +4.5

The source driving the analog inputs should have

a low (< 200

Ω at high frequency) output imped-

ance. Be careful not to overdrive the inputs

outside the power supplies of the ADC (

± 5 V).

Figure 2 shows the buffer circuit used at the

Crystal factory to drive the ADC when perform-

ing FFT testing. See the CS5126 data sheet for

example FFT test results.

Voltage Reference

As shown in Figure 3, an LT1019-5 voltage ref-

erence provides a stable 4.5 V reference for the

ADC. An optional OP27 buffer filters out excess

reference noise and provides a very low output

impedance. To try the unbuffered LT1019-5 di-

rectly, solder in J2 and cut the VREF trace.

Alternatively the shunt reference based reference

schematic given in the CS5126 data sheet can be

evaluated by adding it to the analog patch area.

+15V

-15V

C22

C23

C24

C25

0.22

µF

0.47

µF

+5VA

-5VA

+ C20

µF

C21

µF

0.22

µF

79L05

OUT

COM

78L05

OUT

COM

0.47

µF

C26

+ C27

µF 0.1 µF

+15V

-15V

Analog

Digital

+5V

Logic

TP16

+5VL

Figure 1. Power Supplies

CDB5126

DS32DB5

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