CS5181 Datasheet, PDF (10/24 Pages) Cirrus Logic – Modulator & 400 kHz to 625 kHz 16-Bit ADC

CS5181
VS
+
10 µF
0.1 µF
2.5 V
+
10 µF
0.1 µF
10 µF +
0.1 µF
VREFIN
VREF+
VREF-
CS5181
X1.6
Modulator
VREFOUT
X1
+
10 µF
0.1 µF
+
1 µF
VREFCAP
0.1 µF
Reference
Figure 4. CS5181 connection diagram for using an external voltage reference.
Analog Input
The analog signal to the converter is input into the
AIN+ and AIN- pins. The input signal is fully dif-
ferential with the maximum peak-to-peak ampli-
tude of VREFIN X 1.6 V. The signal needs to have
a common mode voltage in a range from 1.0 V to
VREF + 0.25 V for minimum distortion. A resis-
tor-capacitor filter should be included on the AIN+
and AIN- inputs of the converter. This should con-
sist of a 20 Ω resistor and a 2200 pF capacitor on
each input to ground as illustrated in the system
connection diagram (Figure 11).
Output Coding
Table 1 illustrates the output coding for the con-
verter when operating with the digital filter
(MODE = 1). The converter outputs its data from
the serial port in twos complement format, MSB
first.
The chip offers an MFLAG signal to indicate when
the modulator has gone unstable. MFLAG is set
when an overrange signal forces the modulator into
an unstable condition. Under this condition, output
Fully Differential Bipolar
Input Voltage¹
>(V_FS - 1.5 LSB)
V_FS - 1.5 LSB
-0.5 LSB
-V_FS + 0.5 LSB
<(-V_FS + 0.5 LSB)
Twos Complement
7FFF
7FFF
7FFE
0000
FFFF
8001
8000
8000
Notes: 1. V_FS = VREFIN x 1.6
Table 1. Output Coding.
codes from the converter will be locked to either
plus or minus full scale as is appropriate for the
overrange condition.
Modulator-Only mode
The CS5181 can be operated in modulator-only
mode by connecting the MODE pin to a logic 0
(DGND).
In modulator-only mode the noise-shaped bit-
stream from the fifth-order delta-sigma modulator
is output from the SDO and SDO (inverse bit-
stream) pins.
10
DS250PP1