SLDS216 Data sheet

SLDS216 December 2017 PGA302

PRODUCTION DATA.

9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

9.1 Application Information

The PGA302 device must be paired with an external sensor, and can be used in a variety of applications depending on the chosen sensor. When choosing a sensor, the most important consideration is to ensure that the voltages applied to the analog input pins on the PGA302 stay within the recommended operating range of 0.2 V minimum and 4.2 V maximum. A programmable gain stage allows a wide selection of sensors to be used while still maximizing the input range of the 16-Bit ADC. The PGA302’s internally regulated bridge voltage supply and independent current source for temperature sensors eliminates the need for externally excited sensors. The interface options include I²C and OWI.

9.1.1 0-5V Voltage Output

The 0-5V Analog Output application presents the default PGA302 device in a typical application scenario used as a part of a Sensor Transmitter system.

Figure 115. 0-5V Voltage Output

9.2 Typical Application

Figure 116 shows the schematic for a resistive bridge pressure-sensing application.

PGA302 application-schematic-slds239.gif

Figure 116. Application Schematic

9.2.1 Design Requirements

For this design example, use the parameters listed in Table 65 as the input parameters.

Table 65. Design Parameters

DESIGN PARAMETER	EXAMPLE VALUE
Input voltage range (VDD)	4.5 V to 5.5 V
Input voltage recommended	5 V
Bridge excitation voltage	2.5 V
Input mode	Differential
VINPP and VINPN voltage range	0.2 V to 4.2 V
VINPP and VINPN voltage range	5 kΩ

9.2.2 Detailed Design Procedure

Table 66 shows the recommended component values for the design shown in Figure 116.

Table 66. Recommended Component Values for Typical Applications

DESIGNATOR	VALUE	COMMENT
VINPP resistor (R1) VINPN resistor (R2)	0 Ω	These resistors are in place to determine the cutoff frequency of the lowpass filter created by R1/R2 and C1/C2. When using a resistive bridge these resistors should be 0 Ω (not used) and C1/C2 are calculated based on the bridge resistance.
VINPP capacitor (C1)	0.15 μF	Place as close to the VINPP pin as possible.
VINPN capacitor (C2)	0.15 μF	Place as close to the VINPN pin as possible.
VDD capacitor (C4)	0.1 μF	Place as close to the VDD pin as possible.
DVDD capacitor (C3)	0.1 μF	Place as close to the DVDD pin as possible.

To make use of the full range of the internal ADC it is important to carefully select the sensor to be paired with the PGA302. While the input pins can handle between 0.2 V and 4.2 V, it is good practice to make sure that the common-mode voltage of the sensor remains in middle of this range for differential signals. Note that the P Gain amplifier can be configured to measure half-bridge output, where the half bridge is connected to either VINPP or VINPN, and the remaining pin is internally connected to a voltage of VBRG/2.

To achieve the best performance, take the differential voltage range of the sensor into account. Using proper calibration with a digital compensation algorithm, any voltage range can be mapped to the full range of ADC output values, but the final measurement accuracy will be the highest if the analog voltage input matches the ADC’s input range. The gain of the P Gain amplifier can be selected from 1.33 V/V to 200 V/V to aid in matching the input range of the ADC from –2.5 V to 2.5 V.

9.2.2.1 Application Data

Following is application data measured from a PGA302EVM-037 board. The PGA302 device has been used and was calibrated with three pressure points at one temperature (3P1T) using a resistive bridge emulator board with a schematic as pictured in Figure 117.

PGA302 resistive-bridge-schematic-slds239.gif

Figure 117. Resistive Bridge Emulator Schematic

For setup, the only parameter changed was to increase the PGAIN of the PGA302 device to 40 V/V. After the calibration was performed, the resulting VOUT output voltages were measured at each of the three pressure points and error was calculated based on the expected values as shown in Table 67. Error was calculated using the formula ((VOUT measured – VOUT Expected)/VOUT range) × 100 to account for the expected output range.

Table 67. 3P1T Calibration Accuracy

CALIBRATION POINT	VDD (V)	VINPP - VINPN (mV)	VOUT MEASURED (V)	VOUT EXPECTED (V)	ERROR (%FSR)
P1	4.8642	34.651	0.503	0.5	0.075
P2	4.8602	13.844	2.501	2.5	0.025
P3	4.8589	1.608	4.498	4.5	–0.05%

Additional testing was also done with varying calibration points of 3P3T and 4P4T to show accuracy data across temperature. Table 68 includes 3P3T and 4P4T data at the P2 (2.5-V VOUT) pressure point only. The experimental setup is identical to that used to produce the 3P1T data shown in Table 67 with the exception of the resistive bridge emulator which includes an extra pressure point for four possible calibration points.

Table 68. 3P3T and 4P4T Calibration Accuracy

CALIBRATION METHOD	VOUT VOLTAGE			ERROR, %FSR
CALIBRATION METHOD	–40°C	50°C	150°C	–40°C	50°C	150°C
3P3T	2.494	2.503	2.502	0.0125	0.2625	0.2875
4P4T	2.495	2.501	2.502	0.0375	0.2375	0.3125

9.2.3 Application Curves

Table 69 lists the application curves also found in the Typical Characteristics section.

Table 69. Table of Graphs

GRAPH TITLE	FIGURE
Internal Temperature Sensor	Figure 3
ADE and ADC Linearity Error	Figure 4
AFE and ADC Linearity Error	Figure 5
DAC Linearity Error	Figure 6
Ratiometric Error vs VDD Supply	Figure 7
AFE Gain vs Common-Mode Input	Figure 8