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CS5532/34-BS

12 DS755F3

2. GENERAL DESCRIPTION

The CS5532/34 are highly integrated ∆Σ Analog-

to-Digital Converters (ADCs) which use charge-

balance techniques to achieve 24-bit 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 (CS5532) or four-chan-

nel (CS5534) devices and include a very-low-

noise, chopper-stabilized, programmable-gain in-

strumentation 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-order ∆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

microcontroller, 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

CS5532/34. The front end consists of a multiplexer,

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

programmable-gain, chopper-stabilized instrumen-

tation amplifier. The unity gain buffer is activated

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 50 nA

(MCLK = 4.9152 MHz, see Figure 4).

The instrumentation amplifier is chopper stabilized

and operates with a chop-clock frequency of

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

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

4 Order

∆Σ

Modulator

Programmable

Sinc

Digital Filter

Serial

Port

1000

Ω

1000

Ω

22 nF

C1 PIN

C2 PIN

Figure 3. Multiplexer Configuration

1 2 ... 7 8 9 10 11 12 13 14 15 16 17 ... 49 50

CS5532/34-BS 1

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