CS5372 View Datasheet(PDF) - Cirrus Logic
Part Name
Description
MFG CO.
'CS5372' PDF : 22 Pages View PDF
CS5371/CS5372
VREF- pin connected to VA-. Because most 2.5 V
voltage references require a power supply voltage
greater than 3 V to operate, when powering the
voltage reference from dual ±2.5 V or ±3.0 V sup-
plies the reference voltage into the VREF+ pin is
defined relative to the VA- supply.
The selected voltage reference should produce less
than 1 µVrms of noise in the measurement band-
width on the VREF+ pin. The CS5376 digital filter
output word rate selection determines the band-
width over which voltage reference noise affects
the CS5371/CS5372 modulator dynamic range.
6.1. Voltage Reference Configurations
For a 2.5 V reference, the Linear Technology
LT1019-2.5 voltage reference yields low enough
noise if the output is filtered with a low pass RC fil-
ter as shown in Figure 6. The filtered version in
Figure 6 is acceptable for most spectral measure-
ment applications, but a buffered version with low-
er source impedance, Figure 7, may be preferred
for DC measurement applications. The configura-
tion shown in Figure 7 can use a Linear Technolo-
gy LT1077 or similar low voltage op-amp to buffer
the voltage reference output.
6.2. VREF Input Impedance
Due to the dynamic switched-capacitor input archi-
tecture the input current required from the voltage
reference, and thus the input impedance of the
modulator VREF+ pin, will change any time
MCLK is changed. The input impedance of the
voltage reference input is calculated similar to the
analog signal input impedance as [1 / (f * C)]
where f is the modulator clock frequency, MCLK,
+3 V
10 µF 0.1 µF
Option A
2.5 REF
200 Ω
0.1 µF
+ 68 µF
-3 V
10 µF 0.1 µF
To VREF+
To VREF -
Figure 6. 2.5 Voltage Reference Option A
+3 V
-3 V
10 µu 0.1 µF
Option B
2.5 REF
10 µu 0.1 µF
1k Ω 49.9 Ω
+
+
10k Ω
100 µF
-
AL
+
100 µF
100 Ω
1k Ω
AL
OPAMP
0.1 µF
To VREF+
+ 68 µF
Tant
To VREF -
Figure 7. 2.5 Voltage Reference Option B
12
DS255PP2
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