CS5321 datasheet(23/38 Pages) CIRRUS

23 / 38 page

CS5320/21/22

DS454PP1

2.9 Power Supply Considerations

The system connection diagram, Figure 20, illus-

trates the recommended power supply arrange-

ments. There are two positive power supply pins

for the CS5320/21 and two negative power supply

pins. Power must be supplied to all four pins and

each of the supply pins should be de-coupled with

a 0.1

µF capacitor to the nearest ground pin on the

device.

When used with the CS5322 digital filter, the max-

imum voltage differential between the positive sup-

plies of the CS5320/21 and the positive digital

supply of the CS5322 must be less than 0.25 V. Op-

eration beyond this constraint may result in loss of

analog

performance

the

CS5320/22

and

CS5321/22 system performance.

Many seismic or portable data acquisition systems

are battery powered and utilize dc-dc converters to

generate the necessary supply voltages for the sys-

tem. To minimize the effects of power supply inter-

ference, it is desirable to operate the dc-dc

converter at a frequency which is rejected by the

digital filter, or locked to the modulator sample

clock rate.

A synchronous dc-dc converter, whose operating

frequency is derived from the 1.024 MHz clock

used to drive the CS5322, will minimize the poten-

tial for "beat frequencies" appearing in the pass-

band between dc and the corner frequency of the

digital filter.

2.10 Power Supply Rejection Ratio

The PSRR of the CS5320/21 is frequency depen-

dent. The CS5322 digital filter attenuation will aid

in rejection of power supply noise for frequencies

above the corner frequency setting of the CS5322.

For frequencies between dc and the corner frequen-

cy of the digital filter, the PSRR is nearly constant

at about 60 dB.

2.11 RESET Operation

The RESET pin puts the CS5322 into a known ini-

tialized state. RESET is recognized on the next

CLKIN rising edge after the RESET pin has been

brought high (RESET=1). All internal logic is ini-

tialized when RESET is active.

Normal device operation begins on the second

CLKIN rising edge after RESET is brought low.

The CS5322 will remain in an idle state, not per-

forming convolutions, until triggered by a SYNC

event.

A RESET operation clears memory, sets the data

output register, offset register, and status flags to all

zeroes, and sets the configuration register to the

state of the corresponding hardware pins (PWDN,

ORCAL, DECC, DECB, DECA, USEOR, and

CSEL). The reset state is entered on power on, in-

dependent of the RESET pin. If RESET is low, the

first CLKIN will exit the power on reset state.

2.12 Power-down Operation

The PWDN pin puts the CS5322 into the power-

down state. The power-down state is entered on the

first CLKIN rising edge after the PWDN pin is

brought high. While in the power-down state, the

MCLK and MSYNC signals to the CS5320/21 an-

alog modulator are held low. The loss of the MCLK

signal to the modulator causes it to power-down.

The signals on the MDATA and MFLG pins are ig-

nored. The serial interface of the CS5322 remains

active allowing read and write operations. Informa-

tion in the data register, offset register, configura-

tion register, and convolution data memory are

maintained during power-down. The internal con-

troller requires 64 clock cycles after PWDN is as-

serted before CLKIN stops.

The CS5322 exits the power-down state on the first

CLKIN rising edge after the PWDN pin is brought

low. The CS5322 then enters an idle state until trig-

gered by a SYNC event.

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