CS5180 datasheet(10/28 Pages) CIRRUS

10 / 28 page

CS5180

SYNC pulse should rise on a falling edge of the

MCLK signal. This ensures that the SYNC input to

all CS5180s in the system will be recognized on the

next rising edge of MCLK. Use of the SYNC input

is not necessary to make the converter operate

properly. If it is unused it should be tied to DGND.

Conversion data is output from the SDO and SDO

pins of the device. The data is output from the SDO

pin MSB first, in two’s complement format. The

converter furnishes a serial clock SCLK and its

complement SCLK to latch the data bits; and a data

framing signal, Frame Sync Output (FSO), which

frames the output conversion word. The SCLK

output frequency is MCLK/3.

Clock Generator

The CS5180 must be driven from a CMOS-com-

patible clock at its MCLK pin. The MCLK input is

powered from the VD+ supply and its signal input

should not exceed this supply.

The required

MCLK is 64 × OWR (Output Word Rate). To

achieve an Output Word Rate of 400 kHz, the

MCLK frequency must be 64 × 400 kHz, or

25.6 MHz. A second clock input pin, MCLK,is

not actually used inside the device but allows the

user to run a fully differential clock to the converter

to minimize radiated noise from the PC board lay-

out.

The CS5180 can be operated with MCLK frequen-

cies from 512 kHz up to 26 MHz. The output word

rate

scales

with

the

MCLK

rate

with

OWR = MCLK/64.

Voltage Reference

The CS5180 can be configured to operate from ei-

ther its internal voltage reference, or from an exter-

nal voltage reference.

The on-chip voltage reference is 2.375 V and is ref-

erenced to the AGND pin. This 2.375 V reference is

output from the VREFOUT pin. It is then filtered

andreturnedtothe VREFIN pin. VREFIN pinis

connected to a buffer which has a gain of 1.6. This

scales the on-chip reference of 2.375 V to 3.8 V.

This value sets the peak-to-peak input voltage into

the AIN pins of the converter. Figure 3 illustrates the

CS5180 connected to use the internal voltage refer-

ence. Note that a 1.0 µF and 0.1 µF capacitor are

shown connected to the VREFCAP pin to filter out

noise. A larger capacitor can be used, but may re-

quire a longer reset period when first applying power

to the part to allow for the reference to charge up the

capacitors and stabilize before self-calibration be-

gins.

10 µF

0.1 µF

VREFIN

VREF+

VREF-

VREFOUT

VREFCAP

X1.6

Modulator

Reference

CS5180

10 µF

0.1 µF

1µF

0.1 µF

Figure 3. CS5180 connection diagram for using the internal voltage reference.

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