Semtech SX8724SEVK, Руководство пользователя

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ADVANCED COMMUNICATIONS & SENSING USER GUIDE
SX8724SEVK
Evaluation Kit for SX8724S Data Acquisition System
ACS - Revision 1.0 May 2011
© Semtech Corp.
13.5 Voltage Control
The voltage control allows to select or read the board voltage. This allow the GUI to compute ZoomingADC
parameters and data values function of the registers settings in the GUI, for example the estimated device
performance. V
BATT
is read at the connection of the EVK or when the External V
REF
setting is changed.
Note that the V
BATT
voltage or external V
REF
voltage are estimated according to a 1.22V bandgap reference.
For more precise data values in the GUI, the User has the possibility to set manually the real device voltage
value.
13.6 Estimated Device Performances
These data are theoretical values extracted from registers settings and computed according to the equations
available in the datasheet. The values expressed in Volt units [V] are function of the V
REF
voltage set by the
user ( 13.5. Voltage Control ) in the GUI.
Input impedance – observed input impedance of the first PGA stage that is enabled or the input
impedance of the ADC if all three stages are disabled. Cg multiplied by gain is the equivalent gain
capacitor and Cp is the parasitic capacitor of the first enabled stage. The applied equation is:
Input referred noise – the simple noise model described in the datasheet is used to estimate the equivalent
input referred rms noise V
N,IN
of the acquisition chain. It is computed with the extracted rms output noise
Figure 22. Voltage Control
Figure 23. Computed Data Display
( )
] [
1
Ω
+ ⋅
=
Cp GD Cg
Z
in