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MSP430FR2311: TIA + SAC + comparator

Part Number: MSP430FR2311
Other Parts Discussed in Thread: TIDM-FRAM-IRREFLECTIONSENSING, MSP430F2121, , MSP430FR2353, MSP430FR2355

Hello,

I need to make a IR smoke measurement and choose the best hardware, because the hardware suggested in the "TIDM-FRAM-IRREFLECTIONSENSING" is not enough sensible. I have to read the IR value in two cases: when I have the IR led in On (100us pulsed) and IR led in off. These two values must be different, even if the difference is not so much. With the hardware suggested in the "TIDM-FRAM-IRREFLECTIONSENSING", this difference is very very small, and come times is zero or negative!

So, I ask if it's possible and which is the register configuration for:

1) TIA: the output connected to external pin output without any internal connection

2) SAC: input connected only to external pin. Output connected to external pin and internally to ADC input or eComp input.

Is it possible to do this? If yes, which is the right configuration?

Thank You

Federico Battaglin

  • Hi Federico,

    The two values (IR led on and IR led off) are difference which is based on the difference of received IR light strength. So you need a chamber to reflect IR light from  led emitter and shield the ambient light. The configuration you mentioned is possible. Please refer to the MSP430FR4xx and MSP430FR2xx Family User's Guide (Rev. H) for detail register configuration.

    B.R

    Winter

  • Dear Winter,

    in first, thank You for your answer and schematic and sorry for my delay in reply.

    I just have a smoke chamber and circuit base on MSP430F2121 + external double operational amplifiers chip. This final product works enough well.
    The first OPA works as TIA, instead the second OPA works as integrator so to have a good dynamic range of current amplification.

    But I have to update the schematic using a newer and cheaper solution.
    Following the example, if I connect the TIA directly to ADC, I have the similar ADC value in cases of IR LED ON and OFF, and so I can not use that example even if the schematic is very simple.

    So I need to implement the TIA + Integrator in hardware inside the MSP430FR2311.
    In my schematic, the IN+ of integrator is connected to a dynamic resistive divider so I can choose between two Vin+, in order to change the integrator slope.
    In my schematic, the IN- of integrator is connected, by 2 resistors in serie, to the TIA output: in this way I can reset and discharge my integrator.
    Question 1: is it possible to connect inside the IN+ to the DAC output?
    Question 2: can I implement the integrator using the SAC?

    Finally, 2 questions:
    1) why the TRIO- is multiplexed in 20 pin version? Not good solution, because 16 pin eften is too much low. Is it planned a new version with TRIO- not multiplexed and with more pins?
    2) why there's no version which more FRAM memory? If I need to implement a good smoke detector, 3.75kB is very small quantity. Is it planned a have a new device with more memory?

    Thank You and Best Regards
    Federico Battaglin

  • Hi Federico,

    Thanks for your post.

    Question 1: is it possible to connect inside the IN+ to the DAC output?

    The 6bit-DAC is just for internal comparator and connected to comparator's input. For more details, please see "section 6.11.15 eCOMP0, SAC0, TIA0, and ADC in SOC Interconnection" in MSP430FR2311 datasheet.

    Question 2: can I implement the integrator using the SAC?

    Actually, the SAC of MSP430FR2311 includes a OPA whoes IN+ and IN- can be configured to external pin. Since you can implement your own circuit.

    Finally, 2 questions:
    1) why the TRIO- is multiplexed in 20 pin version? Not good solution, because 16 pin eften is too much low. Is it planned a new version with TRIO- not multiplexed and with more pins?

    Currently, we have no plan for a 20 pin version with dedicated TRIO- pin. Except for smoke detector application, do you have any other function demands to need more pins? The input bias current of TRIO- multiplesed is 5nA. What's your input bias current requirement?

    2) why there's no version which more FRAM memory? If I need to implement a good smoke detector, 3.75kB is very small quantity. Is it planned a have a new device with more memory?

    For high end smoke detector, we recommend our new device MSP430FR2355/2353 which has 4 SAC-L3, including 12 bits-DAC, OPA and PGA. And the FRAM size of MSP430FR2355 IS 32KB, MSP430FR2353 is 16KB version. The configuration of SAC-L3 is more flexible. The input bias current of amplifoer of SAC-L3 is 50 pA. 

    Additional resources: 

    Best Regards,

    If my post helped solve your issue, please click on the  VERIFY ANSWER    button. 

    Winter,

    Search E2E! Your questions may already be answered! 

  • Winter Yu said:

    Hi Federico,

    Thanks for your post.

    Question 1: is it possible to connect inside the IN+ to the DAC output?

    The 6bit-DAC is just for internal comparator and connected to comparator's input. For more details, please see "section 6.11.15 eCOMP0, SAC0, TIA0, and ADC in SOC Interconnection" in MSP430FR2311 datasheet.

    Yes, in the manual at figure 19-1, I see it's possible to connect the DAC-6bit at IN+ of SAC.
    But in the data sheet of MFP430FR2311 there's not electric specification for DAC... is it missing or didn't see it?

    Question 2: can I implement the integrator using the SAC?

    Actually, the SAC of MSP430FR2311 includes a OPA whoes IN+ and IN- can be configured to external pin. Since you can implement your own circuit.

    Ok. I need to fix the Vin+ at 30mV or 90mV. In the first release, the solution is to use an external resistor divider and with additional pin I can modify a bit the voltage in the middle of resistor divider... but it requires an additional pin... and the pins are very low in number (16pin package!)

     

    Finally, 2 questions:
    1) why the TRIO- is multiplexed in 20 pin version? Not good solution, because 16 pin often is too much low. Is it planned a new version with TRIO- not multiplexed and with more pins?

    Currently, we have no plan for a 20 pin version with dedicated TRIO- pin. Except for smoke detector application, do you have any other function demands to need more pins? The input bias current of TRIO- multiplexed is 5nA. What's your input bias current requirement?

    I hope we will plan the 32 pin version!

    More pins are always useful!!!
    Some example that brings me to use the 20pin version:
    * 2-3 pin for 2-wires digital communication to control panel (1: tx, 1 edge rx and, if need 1 level rx)
    * 1-2 for for led indication (now I have only one led, but it's not enough)
    * 1-2 pin for NTC heat sensor (1 pin if I power NTC at 3,3V or share it to parts of circuits; in the first release: 1 pin to power NTC and 1 pin to read the value)
    * 2 pin for I2C for other use (not need for this version, but it's my hope to have it)
    * 2-3 pin for additional sensor, such as CO
    * 2 pins if I have the loop isolator inside

    5nA such as Ibias is enormous value when I use a photodiode! Considering that TRIO- not multiplexed is 50pA, but it's not enough! In my original circuit, that work well (certified in according to EN54), the external operational has 1pA that increase to 20pF at t=+85°C!
    it's clear that to have 50pF is too much to read the value and distinguish the these value when IR led is in ON and in OFF. Instead using a external operational amplifier I can distinguish very very well. So, It's not possible to use the internal TIA connected directly to ADC, as suggested in the example. The TIA for a real smoke detection is not good and not enough! I will try to use a integrator, but the BOM is increased. If You really want to make a chip for smoke detection, eh, ask to the person the work to smoke detector and have experienced to laboratory certification and certificate! I hope You have a plan for a new good chipo for real smoke detection... For example, it needs to add the integrator...

     

    2) why there's no version which more FRAM memory? If I need to implement a good smoke detector, 3.75kB is very small quantity. Is it planned a have a new device with more memory?

    For high end smoke detector, we recommend our new device MSP430FR2355/2353 which has 4 SAC-L3, including 12 bits-DAC, OPA and PGA. And the FRAM size of MSP430FR2355 IS 32KB, MSP430FR2353 is 16KB version. The configuration of SAC-L3 is more flexible. The input bias current of amplifoer of SAC-L3 is 50 pA. 

    Then, 3.75kB for flash is too mush small. I used 3.3kB for a simple smoke and heat detection for addressable fire system with a digital filter for digital 2-wire communication, but I need to add many other things, such as different behaviour at smoke detection, and other feature... 8kB it's a bit enough... 16kB it's ok.

    Take in mind the price must be not similar to MSP430FR2353, that is too much expensive for a single chip solution, because it has too much pins (38 pin) and too much analog modules inside (4 SAC it's too much) and 50pA as too much as Ibias for a real smoke detection.

    If You want to make a new chip for smoke (heat and CO) detection for addressable fire system, it's better to ask to who has real experience and make a partnership! For example, I'm available... ;-)

     

    Additional resources: 

    Best Regards,

    If my post helped solve your issue, please click on the  VERIFY ANSWER    button. 

    Winter,

     

    Thank You a lot for your answer!

     

    Search E2E! Your questions may already be answered! 

  • Dear Winter Yu,
    please, do You have answers for my questions / notes?

    Thank You and Best Regards
    Federico Battaglin
  • Hi Federico,

    Sorry for late. I'd like to summarize your remained questions as below:

    1. But in the data sheet of MFP430FR2311 there's not electric specification for DAC... is it missing or didn't see it?

    [Reply]: Some electric specifications for 6-bit DAC are not released.

    2. I hope we will plan the 32 pin version!

    More pins are always useful!!!
    Some example that brings me to use the 20pin version:
    * 2-3 pin for 2-wires digital communication to control panel (1: tx, 1 edge rx and, if need 1 level rx)
    * 1-2 for for led indication (now I have only one led, but it's not enough)
    * 1-2 pin for NTC heat sensor (1 pin if I power NTC at 3,3V or share it to parts of circuits; in the first release: 1 pin to power NTC and 1 pin to read the value)
    * 2 pin for I2C for other use (not need for this version, but it's my hope to have it)
    * 2-3 pin for additional sensor, such as CO
    * 2 pins if I have the loop isolator inside

    5nA such as Ibias is enormous value when I use a photodiode! Considering that TRIO- not multiplexed is 50pA, but it's not enough! In my original circuit, that work well (certified in according to EN54), the external operational has 1pA that increase to 20pF at t=+85°C!
    it's clear that to have 50pF is too much to read the value and distinguish the these value when IR led is in ON and in OFF. Instead using a external operational amplifier I can distinguish very very well. So, It's not possible to use the internal TIA connected directly to ADC, as suggested in the example. The TIA for a real smoke detection is not good and not enough! I will try to use a integrator, but the BOM is increased. If You really want to make a chip for smoke detection, eh, ask to the person the work to smoke detector and have experienced to laboratory certification and certificate! I hope You have a plan for a new good chipo for real smoke detection... For example, it needs to add the integrator... 

     [Reply]: Thanks for sharing your experience. We will consider your suggestions in our future products. But MSP430FR2311 and MSP430FR235x have many successful examples in our smoke detector customers. So, if 50pA Ibias is not enough, TI still has many 1pA-level operation amplifier products. 

    3.If You want to make a new chip for smoke (heat and CO) detection for addressable fire system, it's better to ask to who has real experience and make a partnership! For example, I'm available... ;-)

      [Reply]: Again, thanks for sharing your experience. We will consider your suggestions in our future products.

     

    Best Regards,

    Winter Yu