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LDC1612: Questions in Snoa949 [Power Reduction Techniques for the Multichannel LDCs in Inductive Sensing Applications]

Part Number: LDC1612
Other Parts Discussed in Thread: LDC2114,

Hello 

Expressions not found in the LDC1612 SPEC sheet appear in this snoa949.

https://www.ti.com/lit/an/snoa949/snoa949.pdf?ts=1591840390864&ref_url=https://www.google.com/

 

t N = t S + t C + t SD + t RB

It is tN or tRB.

The data readback time (tRB) comes out for the first time on page 3 of snoa949. Is it necessary to read data at this timing (immediately after t SD)? If so, what is the trigger to start the readback?

Also, I'm not sure what the relationship between duty cycle and sampling rate is in this article. I don't know what the duty cycle is because I don't have a diagram.

 

I was reading the data with I2C at a proper timing apart from sampling. Is it the wrong way to read data?

Also, this document doesn't quite know when to enter sleep mode. Will it be done during sampling? It looks like a very complicated program.

Could you tell me?

Best regards

Questions in Snoa949.docx

  • Hello, 

    If you are very interested in low power applications with a current consumption being a key factor I highly recommend that you look at our LDC2114 device which is low power and specifically target towards HMI button applications. 

    If you like to use LDC1612 application and are concerned that the power consumption is a concern we have the app note that provides techniques to lower power consumption. The reference to app note is an extension to the datasheet for applications that require low power consumption. 

    If the LDC1612 is configured in multichannel configuration. ts is the sampling time, tc is the conversion time and tsd is the switch delay time. For channel 1 after these times the data is available to be read for Ch1. Since LDC1612 is a 28 bit register depending on the I2C speed the time can be calculated. The LDC1612 device doesn't have any trigger that can be set to be readback but the data and the diagram indicates and assumes that you have a clock that is running at a particular speed. (for eg: 400 Khz) based on teh clock running speed you can estimate the time and control the readback using the uC. 

    As long as the data is readback after ts + tc + tsd the data is OK. There are also flags in teh device known as STATUS flags which can be used to ensure you the data that is read back is after the conversion. The device enables a flag in the status register that can be read. If the INT pin is configured to assert at this status the uC can read start the conversion. More details on how to use the conversion status bits can be fund here

    If you like to take advantage of duty cycle the device needs to be in sleep mode the device needs to be entered by configuring SLEEP_MODE_EN. There is an I2C transaction to put the device in sleep and that is controlled by the uC. 

  • Hello Arjun

    I was surprised at your early reply. Thank you very much. I wonder if you are around me.

    The LDC2114 is a very good sensor IC, but it cannot be used because it is not used in vehicles.
    In my experiment, the LDC1612EVM LDC PCB and coil are controlled by Arduino UNO. RawCode data is also read at 10ms intervals or at an appropriate timing.

    Duty cycle is mentioned in this document, but it's not specifically illustrated and I don't understand this. What do you say in the example in Figure 2?

    tc is the conversion time. Does this time include the time when the conversion data is written to the LDC register (0x00-0x03)?
    I understand that the timing of reading data is independent of the sample rate. Is this correct? Is it always possible to read data from a register using I2C from a microcomputer? For example, it is impossible to read during the time of tc.

    I apologize for my poor understanding.

    Best regards

  • Hello,

    Thanks you for your kind words in regards to our support. We appreciate that. 

    I do agree that the LDC2114 is a good device and perhaps what you are looking for is a Q1 version for automotive applications. We will update you when there is an update on a Q1 version. 

    In regards to Duty Cycle. You can refer to Figure 3 for more information in regards to timing. The duty cycle applies to after performing a full conversion whether in a single channel mode or multichannel mode. For example, after you analysis if the tN is identified as 5mS you can put the device in sleep mode after 5mS and lets say for 50mS and the reengage after after 50mS this is equivalent to 90% duty cycle. 

    The conversion time includes the time it takes for the device to convert the analog signal and measure the digital format. The digital data is then placed in the register 0x00-0x03. The time required to place the converted digital content is minimal when compared to the I2C speed data and conversion time. Since our LDC is an asynchronous system you can always read the data from the register as fast as you can but the data update to the contents is dependent on the conversion time. 

    I hope this answers and clarifies your question if not please reach out to us. 

  • Hello Arjun

    I’m sorry for the late reply.

    Thank you for your detailed answer. I feel like I understand it somehow.

    It means that there is no problem when the Raw Code of the register is read at any time.

    Also

    Duty Cycle = Sleep time / (tN + Sleep time) x 100 [%]

    Does that mean?

    Including the Sleep time in the read cycle feels complicated.

    Does it mean switching to sleep mode at the moment when one 28-bit data is read?

    Of course, that requires external control, right?

    Best regards

  • Hello,

    Yes, thats correct. You can choose to put the device in sleep mode once you have read the 28 bits of data. All of the timing needs to be controlled externally and managed through the mcu that is being used. 

  • Hello Arjun

    Thank you for your prompt reply.

    I understood that. 

    It's a bit off, but is there no plan to release an in-vehicle version of the LDC2114?

    Why is there no Q1 version on the LDC2114?  Please tell me as much as you can understand.

     

    Best regards

  • We will certainly keep you posted if and when LDC2114-Q1 is made available. Thanks for your interest in our parts.

  • Hello Arjun

    Thank you for your quick reply.

    We hope LDC2114-Q1 will be released soon.

    Best regards