Datasheet

SDA
SCL
A0
A1
INT
IN0
ADC128D818
GND
V+
IN1
IN2
IN3
IN4
VREF
IN5
IN6
IN7
LM4140
+
+
0.1 PF
1
2
1
1
Bridge Sensor
R2
+
-
Instrumentation
Op-Amp
Microcontroller
V+
V+
RB_top
R
R
R
RB_bottom
R2
R2
R2
1 PF
0.1 PF
1 PF
RB_top
RB_bottom
ADC128D818
SNAS483E –FEBRUARY 2010–REVISED MARCH 2013 www.ti.com
Bridge Sensors
Figure 39. Bridge Sensor Application
ADC128D818 is perfect for transducer applications such as pressure sensors. These sensors measure pressure
of gases or liquids and produce a pressure-equivalent voltage at their outputs. Figure 39 shows a typical
connection of a pressure sensor, represented by the bridge sensor.
Most pressure sensor has a low sensitivity characteristic, which means its output is typically in the millivolts
range. Because of that reason, an op-amp, such as an instrumentation amplifier, can be used for the gain stage.
The positive aspect of this configuration is its ratiometric connection. A ratiometric connection is when the ADC’s
VREF and GND are connected to the bridge sensor’s voltage references. With a ratiometric configuration,
external VREF accuracy can be ignored.
Layout and Grounding
Analog inputs will provide best accuracy when referred to the GND pin or a supply with low noise. A separate,
low-impedance ground plane for analog ground, which provides a ground point for the voltage dividers and
analog components, will provide best performance but is not mandatory. Analog components such as voltage
dividers should be located physically as close as possible to the ADC128D818.
REGISTER MAP
ADC128D818 Internal Registers
Table 8. ADC128D818 Internal Registers
Register
Read/ Default Value Register
Register Name Address Register Description
Write [7:0] Format
(hex)
Configuration Register R/W 00h 0000_1000 Provides control and configuration 8-bit
Provides status of each WATCHDOG limit or
Interrupt Status Register R 01h 0000_0000 8-bit
interrupt event
Masks the interrupt status from propagating
Interrupt Mask Register R/W 03h 0000_0000 8-bit
to INT
Conversion Rate Register R/W 07h 0000_0000 Controls the conversion rate 8-bit
Disables conversion for each voltage or
Channel Disable Register R/W 08h 0000_0000 8-bit
temperature channel
Initiates a single conversion of all enabled
One-Shot Register W 09h 0000_0000 8-bit
channels
Deep Shutdown Register R/W 0Ah 0000_0000 Enables deep shutdown mode 8-bit
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