CS5374 datasheet(30/44 Pages) CIRRUS

30 / 44 page

CS5374

DS862F1

VOLTAGE REFERENCE

The CS5374 modulators require a 2.500 V preci-

sion voltage reference to be supplied to the VREF

pins.

7.1 VREF Power Supply

To guarantee proper regulation headroom for the

voltage reference device, the voltage reference

GND pin should be connected to VA– instead of

system ground, as shown in Figure 18. This con-

nection results in a VREF– voltage equal to VA–

and a VREF+ voltage very near ground potential

[(VA–) + 2.500 VREF].

Power supply inputs to the voltage reference device

should be bypassed to system ground with 0.1

μF

capacitors placed as close as possible to the power

and ground pins. In addition to 0.1

μF local bypass

capacitors, at least 100

μF of bulk capacitance to

system ground should be placed on each power

supply near the voltage regulator outputs. Bypass

capacitors should be X7R, C0G, tantalum, or other

high-quality dielectric type.

7.2 VREF RC Filter

A primary concern in selecting a precision voltage

reference device is noise performance in the mea-

surement bandwidth. The Linear Technology

LT1019AIS8-2.5 voltage reference yields accept-

able noise levels if the output is filtered with a low-

pass RC filter.

A separate RC filter is required for each device

connected to the voltage reference output. Signal-

dependent sampling of the voltage reference by one

system device could cause unwanted tones to ap-

pear in the measurement bandwidth of another sys-

tem device if a single VREF RC filter is common

to both.

7.3 VREF PCB Routing

To minimize the possibility of outside noise cou-

pling into the CS5374 voltage reference input, the

VREF

± traces should be routed as a differential

pair from the large capacitor of the voltage refer-

ence RC filter. Careful control of the voltage refer-

ence source and return currents by routing VREF

as a differential pair will significantly improve im-

munity from external noise.

To further improve noise rejection of the VREF

differential route, include 0.1

μF bypass capaci-

tors to system ground as close as possible to the

VREF+ and VREF– pins of the CS5374.

7.4 VREF Input Impedance

The switched-capacitor input architecture of the

VREF

± inputs results in an input impedance that

depends on the internal capacitor size and the

MCLK frequency. With a 15 pF internal capacitor

and a 2.048 MHz MCLK, the VREF input imped-

ance

approximately

To VREF+

From VA+

Regulator

2.500 V

VREF

0.1

μF

To VREF-

0.1

μF

100

μF

0.1

μF

0.1

μF

0.1

μF

100

μF

100

μF

From VA-

Regulator

Route VREF

± as a differential pair

from the 100uF RC filter capacitor

Figure 18. Voltage Reference Circuit

CS5374 датащи(PDF) 30 Page - Cirrus Logic

CS5374 датащи(HTML) 30 Page - Cirrus Logic

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

датащи скачать

ссылки URL