Cirrus Logic CDB5374 - Manual (Page 19)

CDB5374
DS862DB1 19
2.2.5 Voltage Reference
A voltage reference on CDB5374 creates a precision voltage from the regulated analog supplies for the
modulator and test DAC VREF inputs. Because the voltage reference output is generated relative to the
negative analog power supply, VREF+ is near GND potential for bipolar power supplies.
2.2.5.1 VREF_MOD12, VREF_MOD34, VREF_DAC
The voltage reference output is provided to the CS5374
∆Σ modulators and the CS4373A test DAC
through separate low-pass RC filters. By separately filtering the voltage reference for each device, signal-
dependent sampling of VREF by one device is isolated from other devices. Each voltage reference signal
is routed as a separate differential pair from the large RC filter capacitor to control the sensitive VREF
source-return currents and keep them out of the ground plane. In addition to the RC filter function, the
100 uF filter capacitor provides a large charge well to help settle voltage reference sampling transients.
2.2.5.2 Common Mode Bias
A buffered version of the voltage reference is created as a low-impedance common mode bias source for
the analog signal inputs. The bias resistors connected between the buffered voltage reference and each
analog signal input half depends on the sensor type and should be modified to match the sensor manu-
facturer recommendations.
Specification Value
Precision Reference - Linear Tech
LT1019AIS8-2.5
Surface Mount Package Type SO-8
Output Voltage Tolerance +/- 0.05%
Temperature Drift 10 ppm / degC
Quiescent Current 0.65 mA
Output Voltage Noise, 10 Hz - 1 kHz 4 ppm
RMS
Ripple Rejection, 10 Hz - 200 Hz > 100 dB