Texas Instruments ADS1675REF, Руководство пользователя, Страница: 6 / 24

R18
0 W
R15
249
W
R20
10
W
R13
249
W
R19
10
W
R17
0
W
C17
750pF
AINP
AINN
V
IN+
V
IN
-
COM
VOUT -
VOUT+
8
2
1 4
5
PD
V
S+
V
S
-
V
S -
V
S -
THS4503ID
C40
10 F
m
C39
0.1 F
m
-
VCC
C38
10 F
m
C37
0.1 F
m
+VCC
RCM
JP1
6
C14
Not Installed
C72
C12
3 7
Not Installed
Not Installed
Digital Interface
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To maximize the dynamic range of the THS4503 and reduce the THD impact from this amplifier, +9V and
–4V are used for this THS4503. This configuration gives a maximum ±6.5V swing range.
Figure 1
illustrates the typical analog input section of the ADS1675REF.
Figure 1. ADS1675REF Schematic: Typical Analog Input Section
5 Digital Interface
The ADS1675REF is designed for easy interfacing with the USB2.0 interface for use with the XEM3010
board. The ADS1675REF kit also provides ADCPro software so that the user can configure the ADS1675
and read out the captured data through the USB interface on the XEM3010 board.
6 Reference Voltage
The ADS1675REF provides a 3.0V reference source via a REF5030 (U2) and OPA211A (U5) to provide a
high-quality reference voltage for ADS1675. The REF5030 (U2) generates the 3.0V reference signal. The
output of the REF5030 is heavily filtered to remove noise. The onboard OPA211 (U5) again filters and
buffers the reference signal so that the reference signal noise to the ADS1675 is less than the noise
generated by the converter itself. The OPA211 is a low-noise, unity-gain stable amplifier that provides a
reliable current source for the ADS1675 reference input. The OPA211 and output decoupling capacitors
work together to settle the VREFP (ADS1675) reference input voltage to within ±1/2 LSB, every 50ns. This
board uses a 10
m
F ceramic capacitor with a 0.1
m
F ceramic capacitor directly across the reference inputs,
VREFP and VREFN. Note that the 10 m F and 0.1 m F capacitors are placed as close to the ADS1675
reference pins as possible. These capacitors further reduce noise that is common to both inputs. The
ADS1675 VREFN pin goes to ground.
6 ADS1675REF SBAU162A – December 2009 – Revised September 2010
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