CS5531-AS datasheet(14/52 Pages) CIRRUS

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CS5531/32/33/34

DS289PP5

2. GENERAL DESCRIPTION

The CS5531/32/33/34 are highly integrated

∆Σ An-

alog-to-Digital Converters (ADCs) which use

charge-balance

techniques

achieve

16-bit

(CS5531/33) and 24-bit (CS5532/34) performance.

The ADCs are optimized for measuring low-level

unipolar or bipolar signals in weigh scale, process

control, scientific, and medical applications.

To accommodate these applications, the ADCs

come as either two-channel (CS5531/32) or four-

channel (CS5533/34) devices and include a very

low noise chopper-stabilized programmable gain

instrumentation amplifier (PGIA, 6 nV/

√Hz @0.1

Hz) with selectable gains of 1×, 2×, 4×, 8×, 16×,

32×, and 64×. These ADCs also include a fourth or-

der

∆Σ modulator followed by a digital filter which

provides twenty selectable output word rates of 6.25,

7.5, 12.5, 15, 25, 30, 50, 60, 100, 120, 200, 240, 400,

480, 800, 960, 1600, 1920, 3200, and 3840 Samples

per second (MCLK = 4.9152 MHz).

To ease communication between the ADCs and a

micro-controller, the converters include a simple

three-wire serial interface which is SPI and Mi-

crowire compatible with a Schmitt Trigger input on

the serial clock (SCLK).

2.1. Analog Input

Figure 3 illustrates a block diagram of the

CS5531/32/33/34. The front end consists of a multi-

plexer, a unity gain coarse/fine charge input buffer,

and a programmable gain chopper-stabilized instru-

mentation amplifier. The unity gain buffer is activat-

ed any time conversions are performed with a gain

of one and the instrumentation amplifier is activated

any time conversions are performed with gain set-

tings greater than one.

The unity gain buffer is designed to accommodate

rail to rail input signals. The common-mode plus

signal range for the unity gain buffer amplifier is

VA- to VA+. Typical CVF (sampling) current for

the unity gain buffer amplifier is about 500 nA

(MCLK = 4.9152 MHz, see Figure 4).

The instrumentation amplifier is chopper-stabi-

lized and operates with a chop clock frequency of

MCLK/128. The CVF (sampling) current into the

instrumentation amplifier is typically 500 pA over

VREF+

Sinc

Digital

Filter

XGAIN

AIN2+

AIN2-

AIN1+

AIN1-

CS5531/32 IN+

IN-

AIN4+

AIN4-

AIN1+

AIN1-

CS5533/34

IN+

IN-

IN+

IN-

GAIN is the gain setting of the PGIA (i.e. 2, 4, 8, 16, 32, 64)

VREF-

Differential

Order

∆Σ

Modulator

Programmable

Sinc

Digital Filter

Serial

Port

1000

Ω

1000

Ω

22 nF

C1 PIN

C2 PIN

Figure 3. Multiplexer Configuration

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