CS5532 datasheet(13/50 Pages) CIRRUS

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CS5532/34-BS

DS755F3

instrumentation amplifier is typically 1200 pA

over

-40°C to +85°C (MCLK=4.9152 MHz).

The common-mode plus signal range of the instru-

mentation amplifier is (VA-) + 0.7 V to (VA+) -

1.7 V.

Figure 4 illustrates the input models for the ampli-

fiers. The dynamic input current for each of the

pins can be determined from the models shown.

Note:

The C=3.9pF and C = 14pF capacitors are

for input current modeling only. For physical

input capacitance see ‘Input Capacitance’

specification under Analog Characteristics.

2.1.1. Analog Input Span

The full-scale input signal that the converter can

digitize is a function of the gain setting and the ref-

erence voltage connected between the VREF+ and

VREF- pins. The full-scale input span of the con-

verter is ((VREF+) - (VREF-))/(GxA), where G is

the gain of the amplifier and A is 2 for VRS = 0, or

A is 1 for VRS = 1. VRS is the Voltage Reference

Select bit, and must be set according to the differen-

tial voltage applied to the VREF+ and VREF- pins

on the part. See section 2.3.5 for more details.

After reset, the unity gain buffer is engaged. With a

2.5 V reference this would make the full-scale input

range default to 2.5 V. By activating the instrumen-

tation amplifier (i.e. a gain setting other than 1) and

using a gain setting of 32, the full-scale input range

can quickly be set to 2.5/32 or about 78 mV. Note

that these input ranges assume the calibration regis-

ters are set to their default values (i.e. Gain = 1.0 and

Offset = 0.0).

2.1.2. Multiplexed Settling Limitations

The settling performance of the CS5532/34 in mul-

tiplexed applications is affected by the single-pole,

low-pass filter which follows the instrumentation

amplifier (see Figure 3). To achieve data sheet set-

tling and linearity specifications, it is recommend-

ed that a 22 nF C0G capacitor be used. Capacitors

as low as 10 nF or X7R type capacitors can also be

used with some minor increase in distortion for AC

signals.

2.1.3. Voltage Noise Density Performance

Figure 5 illustrates the measured voltage noise

density versus frequency from 0.025 Hz to 10 Hz

of a CS5532-BS. The device was powered with

±2.5 V supplies, using 30 Sps OWR, the 64x gain

range, bipolar mode, and with the input short bit

enabled.

AIN

Gain =2, 4,8,16, 32,64

C =3 .9 pF

Gain = 1

AIN

C= 14 pF

φ Coarse

φ Fine

≤ 12 mV

i= fV

≤ 8mV

i= fV

MCLK

128

MCLK

Figure 4. Input models for AIN+ and AIN- pins

100

1000

0.025

0.10

1.00

10.00

Frequency (Hz)

Figure 5. Measured Voltage Noise Density, 64x

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