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INA180-Q1: Automotive current modulation interface

Shinji Tsuji
Genius 13188 points
Part Number: INA180-Q1
Other Parts Discussed in Thread: INA240, INA381, INA290-Q1, INA303, INA302, INA301, INA180, INA293-Q1, INA181, TINA-TI, INA200-Q1, INA302-Q1, TLV3201-Q1, , TLV4021, INA185, TLV3201, INA293

Hi team,

I would like to decode the signal from the sensor which is superimposed on to the power line(5V to 9V).

Power is sourced by regulator and the signal is transmitted by the sensor by alternating its load current.

The interface is a current modulation from 20mA to maximum 70mA. The data is Manchester coded binary data and its current amplitude can

be adjusted from 20mA to 70mA.

I would like to sense the load current by shunt resistor on the power rail(5V to 9V) and would like to decode the Manchester code.

Could you advise the best possible solution to achieve this?

regards,

  • 0
    Guru 140200 points

    Hi Shinji,

    what about the data rate?

    Kai

  • 0
    TI__Mastermind 31355 points

    Hey Shinji,

    This will only be possible if the amplifier has a BW exceeding the data rate of the encoding. Specifically as a minimum, the amplifier output needs to settle to final value before the HIGH or LOW time of the bit could change. So we really need the data rate/frequency here to know if a current sense amplifier (CSA) could be used.

    There are other considerations. So is the current switching between 20mA and 70mA? So is 20mA = LOW and 70mA = HIGH? If this is the case, then you could use a uni-directional CSA (no REF pin).

    If current can switch from 0mA to 20mA, then you will need a bidirectional CSA (REF pin included). Maybe this could be a startup condition? How quickly does the encoding begin after the rail is powered up? How quickly does decoding need to begin after power up? Answering this question will dictate whether or not you need a unidirectional or bidirectional device.

    The REF pin allows you to offset the amplifier so you can avoid output saturation, which will slow down output response. 

    Devices I would look into are the INA290-Q1, INA293-Q1, INA301/INA302/INA303, INA240, INA180, INA381 and INA181.

    The INA290-Q1 and INA293-Q1 offer the best bandwidth and thus settling time, but are unidirectional. The INA302 has good BW and best slew rate and also comes with integrated window comparators that could be used to decode the Manchester coding transitions. The INA180 (unidirectional) and INA181 (bidirectional) are decently fast and cheaper. The INA381 is very similar to INA181, but includes integrated comparator.

    Please consider using TINA-TI spice simulator. All of the devices I mention have models that model BW and slew rate and can easily show performance for measuring a square wave current signal.

    Hope this makes sense and helps out.

    Best,

    Peter

  • 0 in reply to Peter Iliya
    TI__Genius 13188 points

    Hi Peter,

    Thank you for your response. I will look into more detail about the interface spec especially data rate.

    regards,

  • 0 in reply to Shinji Tsuji
    TI__Genius 13188 points

    Hi Peter,

    Data rate is 250kbps maximum.

    current is 20mA = low, 70mA( or selectable between 40mA to 70mA) = High.

    I need Q100 device.

    Do you have a plan to release Q100 version of INA381?

    Or INA200-Q1 could be a candidate?

    regards,

  • 0 in reply to Shinji Tsuji
    Guru 140200 points

    Hi Shinji,

    the comparators of INA200-Q1 and INA381A1 are not fast enough to generate a symmetric square wave with a 125k clock (250kBaud). So, I would give this circuit with the INA302A2 a try:

    shinji_ina302a2.TSC

    Well, it also shows a propagation delay, but it's symmteric with nearly equal low-to-high and high-to-low propagations delays. So, the digital transmission can very well be decoded, at least in the simulation.

    Kai

  • 0 in reply to kai klaas69
    TI__Genius 13188 points

    Hi Kai,

    Thank you very much for you support.

    INA302-q1 seems a bit expensive.

    How about INA180-Q1 + TLV3201-Q1 combined solution?

    Total cost is lower than INA302-q1 and still seems to meet the requirement from the spec.

    Does it meet this requirement?

    regards,

  • 0 in reply to Shinji Tsuji
    TI__Mastermind 31355 points

    Hey Shinji,

    Consider this circuit using the INA185A1 and TLV4021: https://www.ti.com/lit/an/sboa349/sboa349.pdf. The INA185 does not come in Q100, but it very similar to the INA180A1-Q1 so the design procedure can be used. In order to meet the requirement the output should reach the comparator threshold voltage in a couple microseconds, so before the end of the ON time (4us). You can approximate the rise time of an amplifier with tr = 0.35/BW. So for the INA180A1, the rise time to about 90% final value is 0.35/350kHz = 1us. 

    So as long as the TLV3201 propagation delay is < 2us, then your idea should work.

    Please test in simulation to verify and check the TLV3201 datasheet.

    Best,

    Peter

  • 0 in reply to Shinji Tsuji
    Guru 140200 points

    Hi Shinji,

    the "A2" versions of INA180 and INA185 are not fast enough, for my taste:

    But the "A1" versions are better:

    Provided the models are correct...

    Kai

  • 0 in reply to kai klaas69
    TI__Genius 13188 points

    Hi Kai,

    Thank you very much.

    This is mostly due to the slow Slew rate(2V/us) of the device?

    Do you have a higher slew rate version of these devices?

    regards,

  • 0 in reply to Shinji Tsuji
    TI__Mastermind 27715 points

    Hello Shinji,

    Currently the only device we offer with a faster slew rate is the INA293, with a typical of 2.5V/us, or the INA302 with 4V/us as Peter mentioned before. For faster slew rate, you will need to use a different circuit configuration with a faster op amp.

    Best regards,

    Ian Williams
    Applications Manager
    Current Sensing

  • 0 in reply to Shinji Tsuji
    Guru 140200 points

    Hi Shinji,

    yes, the slew rate is an important parameter. Because of that I recommended the INA302 with its 4V/µs slew rate.

    Kai