Cirrus Logic CS5534-BS - Manual (Page 12)

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 1Ч, 2Ч, 4Ч, 8Ч,
16Ч, 32Ч, 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
M
U
X
AIN2+
AIN2-
AIN1+
AIN1-
CS5531/32 IN+
IN-
AIN4+
AIN4-
*
*
*
AIN1+
AIN1-
CS5533/34
M
U
X
IN+
IN-
IN+
IN-
GAIN is the gain setting of the PGIA (i.e. 2, 4, 8, 16, 32, 64)
X1
X1
X1
VREF-
X1
Differential
4 Order
∆Σ
Modulator
th
5 Programmable
Sinc
Digital Filter
3 Serial
Port
1000 Ω
1000
Ω
22 nF
C1 PIN
C2 PIN
X 1
X 1
Figure 3. Multiplexer Configuration