Texas Instruments | PGA900, PGA300 and PGA305 Use Case for HVAC Applications | Application notes | Texas Instruments PGA900, PGA300 and PGA305 Use Case for HVAC Applications Application notes

Texas Instruments PGA900, PGA300 and PGA305 Use Case for HVAC Applications Application notes
____________________________________________________
PGA900, PGA300 and PGA305 Use Case for HVAC
Applications
Introduction
The resistive bridge sensors are used in a variety of
end-equipment like Pressure Transmitters or
Transducers, Flow Meters, HVAC, and Weight Scales.
HVAC has the sensor transmitter to measure the
pressure and temperature and input the controller, and
the controller will send an output signal to valves,
actuators, and motor drives based on the needed
environmental conditions.
HVAC
The HVAC needs to measure precisely, so need the
following spec in signal conditioning device:
• High resolution
• High accuracy
• Temperature compensation and linearization
• Output interface : voltage of 4 to 20 mA or I2C
Evaporator
PGA900
T1
Figure 3 shows the PGA900 functional diagram. The
device has two high-resolution ADCs (24-bit) with an
integrated ARM M0 MCU that allows the development
of application specific compensation linearization
algorithms. The PGA900 supports multiple output
choices, including the analog voltage (0 – 5, 0 – 10 V),
the current output (4 – 20 mA), and the digital I2C,
UART, PWM, and One Wire interface.
Valve
Compressor
M
P2
Figure 2. Resistive Bridge
Important System Factors
Figure 1 shows the HVAC mechanism. The HVAC
system measures and monitors the air temperature
and pressure for both the evaporator (T1 and P1) and
condenser (T2 and P2) to control the environmental
condition. The sensor element to measure the
pressure value is normally the resistive bridge.
Figure 2 shows the resistive bridge.
P1
Pressure
T2
Condenser
PGA900
Figure 1. HVAC System
RATIOMETRIC
BRIDGE EXCITATION
VBRGP
REFERENCE
VINPP
PGA
VINPN
24-bit
ADC
SOFTWARE
AND DATA
MEMORY
POWER MANAGEMENT
OWI
VDD
(3.3 ± 30 V)
SPI,
UART
MISO/TX,
MOSI/RX,
CSN, SCK
I2C
SCL, SDA
RESISTIVE SENSING AFE
VBRGN
VINTP
MUX
Figure 2 shows the resistive bridge. Ideally, the signal
from the resistive bridge would be linear with the
change of pressure, but that is not always the case.
Furthermore, each individual resistance is not equal to
the others, so a voltage offset is observed. This
particularly comes to effect when no pressure is
applied to the resistive bridge. Finally, the output is
temperature-dependent, meaning the signal from the
resistive bridge must be temperature-compensated in
the system. This requires that the typical system
connected to a load cell sensor is capable of
linearization and temperature dependency cancellation
for accurate measurements across pressure and
temperature.
EEPROM
VINTN
PGA
24-bit
ADC
CONTROL
AND
STATUS
REGISTERS
TOPDIG,
TONDIG
PWM
14-bit
DAC
GAIN
VOUT
TEMPERATURE SENSING AFE
INTERNAL
TEMPERATURE
SENSOR
DIAGNOSTICS
ARM
CORTEX M0
(PROGRAMMABLE
BY USERS)
INTERNAL
OSCILLATOR
DEBUGGER
SWDIO,
SWDCLK
Figure 3. PGA900 Block Diagram
SPACER
SPACER
SPACER
SPACER
SPACER
SLYA025 – February 2017
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PGA900, PGA300 and PGA305 Use Case for HVAC Applications
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PGA300
PGA305
RATIOMETRIC
BRIDGE EXCITATION
REFERENCE
EEPROM
POWER MANAGEMENT
PGA
RESISTIVE SENSING AFE
MUX
VINTP
VINTN
PGA
INTERNAL
TEMPERATURE
SENSOR
DIAGNOSTICS
VINTP
VINTN
VDD
(3.3 ± 30 V)
CONTROL
AND
STATUS
REGISTERS
I2C
SCL, SDA
PGA
14-bit
DAC
24-bit
ADC
GAIN
VOUT
TEMPERATURE SENSING AFE
GAIN
INTERNAL
TEMPERATURE
SENSOR
3rd ORDER TC & 3rd
ORDER NL
SENSOR
COMPENSATION
DIAGNOSTICS
INTERNAL
OSCILLATOR
Figure 5. PGA305 Block Diagram
VOUT
Device
Optimized Parameters
Performance Trade-Off
PGA308
High Gain Setting,
Automotive AECQ100
available
High current consumption
PGA309
High Gain Setting
High current consumption
INTERNAL
OSCILLATOR
Figure 4. PGA300 Block Diagram
Table 2. Adjacent Tech Notes
PGA305
Figure 5 shows the PGA305 Block Diagram. This
device integrates a dual-channel, 24-bit ADC, followed
by a 3rd-order digital linearity compensation algorithm.
The system accuracy achieved can be <0.1%FS over
temperature. The PGA305 supports the analog voltage
and the current output (4 – 20 mA), along with the I2C
output and the One Wire Interface.
2
OWI
24-bit
ADC
RESISTIVE SENSING AFE
TEMPERATURE SENSING AFE
OPTIONAL
EXTERNAL
TEMPERATURE
SENSOR
POWER MANAGEMENT
Table 1. Alternative Device Recommendations
14-bit
DAC
3rd ORDER TC & 3rd
ORDER NL
SENSOR
COMPENSATION
EEPROM
REFERENCE
VBRGN
CONTROL
AND
STATUS
REGISTERS
24-bit
ADC
PGA
VINPN
24-bit
ADC
VBRGN
RATIOMETRIC
BRIDGE EXCITATION
VINPP
VDD
(3.3 ± 30 V)
OWI
VINPP
VINPN
BRIDGE
SENSOR
OPTIONAL
EXTERNAL
TEMPERATURE
SENSOR
PGA300
VBRGP
VBRGP
MUX
Figure 4 shows the PGA300 Block Diagram. The
PGA300 integrates two 16-bit ADCs while a 3rd-order
compensation algorithm is employed for sensor
linearization. The system accuracy achieved can be
<0.1%FS over temperature. PGA300 supports the
analog voltage, the current output (4 – 20 mA), and
the One Wire interface.
SLYA025
PGA900/300/305 Use Case for the HVAC
Application
SLYA026
PGA900/300/305 Use Case for the
Pressure Transmitter Application
PGA900, PGA300 and PGA305 Use Case for HVAC Applications
Copyright © 2017, Texas Instruments Incorporated
SLYA025 – February 2017
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