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Precision Amplifiers Forum
Auto calibration Algoritm
1-I want use pga309 in my design with strain gauge , please explain for auto calibration process .
2- how much maximum current for Vexc for non linear bridge sensor?
Thank you very much.
Thank you for your interest in the PGA309.
Ian WilliamsLinear Applications EngineerPrecision Analog and Sensing Products
Hi Ian It is possible to use an catalytic sensor with the pga309? I'm asking because is a bridge sensor and I'm wondering if this could work.
If it is a bridge sensor, it should work with the PGA309. If you provide a link to a data sheet for the sensor I can take a more thorough look.
here is the link to the datasheet of the sensor : http://www.citytech.com/PDF-Datasheets/4p75ct4.pdf
Only needs a few external resistor to complete the bridge.
There's an application note (SBOA10) that explain that connecting the TEST pin to Vcc, the I2C will be released (In my case I won't need the EEPROM Memory). I will be using the pga309 with the msp430f2274. I have a question regarding the Test Pin in the pga309:
In the application note pag3 says that :
"it may be optimal for the microcontroller to control the Test pin in order to keep VOUT at high impedance until the microcontroller has configured the PGA309 for the desired settings"
But in pag1 says that if the Test pin is pulled high: a microcontroller can modify the register and that Vout will be enable.
Is this a contradiction? What I understand of this is that I need to pull high the Test Pin to configure the registers but in that case Vout will be enable too.
How can I modify the registers of the pga309 while keeping Vout at high impedance?
This configuration only need to be done once, at the beginning of the program or requires multiple configs?
The only issue I can see is the high current consumption of the sensor (75 ±7 mA). This exceeds the PGA309's maximum VEXC current of 50mA. Therefore you would need a separate power supply for the sensor.
If I understand correctly, you desire the following operation from your system (PGA309 + MSP430):
1. Power on system, PGA309 VOUT at high impedance2. Use MSP430 to configure PGA309 registers3. Enable PGA309 VOUT
It is entirely possible to achieve this. Simply keep the TEST pin low ('0') at power-up so that the PGA309 begins its usual power-up sequence. VOUT will be disabled and the PGA309 will attempt to read its register settings from an external EEPROM. Since the EEPROM will not be present, VOUT will not enable. You can then write the initial register settings to the PGA309 using your MSP430 (with the TEST pin still low), since the power-on state machine cycle will reset once you address the PGA309 over the communication bus. Once the settings have been written, you can bring the TEST pin high ('1'), VOUT will enable, and at that point you have full control over the registers.
The above information comes from section 3.1, "Power-On Sequence and Normal Stand-Alone Operation," of the PGA309 User's Guide.
Please disregard my previous comment about the current requirements of the catalytic sensor. As I stated in an earlier post on this thread, you can use a pull-up resistor to VCC to provide the additional current. The attachment contains more information and a simulation to support this.
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