AS1545
Datasheet - Detailed Description
Figure 38. Definition of Fully Differential Input
RANGE = 1
0 < VCM < VDD
0 < AIN-, AIN+ < VDD
RANGE = 0 0 < VCM < VDD
VIN
VIN
0 < AIN-, AIN+ < VDD
AIN+
AIN+
±VREF/2
±VREF
VCM
VCM
AIN-
AIN-
t
t
Pseudo Differential Mode
The AS1545 consists of six pseudo differential pairs. In pseudo differential mode, AIN+ is connected to the signal
source with an amplitude of VREF or 2 × VREF (depending on the range selected) to make use of the full dynamic range
of the part. A dc input is applied to the AIN- pin. The voltage applied to this input provides an offset from ground or a
pseudo ground for the AIN+ input. The benefit of pseudo differential inputs is that they separate the analog input signal
ground from the ADC’s ground allowing dc common-mode voltages to be cancelled. Figure 39 shows a connection
diagram for pseudo differential mode.
Figure 39. Pseudo Differential Mode Connection Diagram
+
VREF p-p
VIN+
AS1545
-
REFA/
VIN-
REFB
DC Input Voltage
4.7µF
Figure 40. Definition of Pseudo Differential Input
0 < AIN-, AIN+ < VDD
RANGE = 0
0 < AIN-, AIN+ < VDD
RANGE = 1
VIN
VIN
AIN+
AIN+
AIN- + VREF
AIN- + 2VREF
VREF
2VREF
AIN-
AIN-
t
t
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