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TIDA-00914: TIDA-00914

Part Number: TIDA-00914
Other Parts Discussed in Thread: TMS320F28379D, AMC1306M25, AMC1306M05, AMC3306M05, AMC3306M25, INA240, INA241A, AMC1035, ADS7042, LMG1210, ISO6760

My customer is considering a new generation of servo driver design based on the TIDA-00914 reference design, which requires high precision, but there are some differences in parameters, and needs to confirm with TI engineers whether changes are needed.

Let's start with the characteristics of the two products: (customer's product referred to as CC-MD)

TIDA-00914 features:

  • Reinforced Isolated Inverter Power Stage Suited for 200- to 480-V AC Powered Drives;
  • Nominal Phase Current Measurement Range of 28 ARMS, Transient Peak Range of ±80 Apk With 4-mΩ Shunt Resistor;
  • IGBTs are used;
  • Control by TMS320F28379D;

Features of CC-MD: (customer's features abbreviated as CC-MD)

  • 24- to 60-V DC Powered Drives;
  • Nominal Phase Current Measurement Range of 40 ARMS, Transient Peak Range of ±80 Apk;
  • With MOSFETs or GaN FETs.
  • Control by FGPA.

The above 4 features are the main differences, so CC-MD products with such characteristics are suitable for the ΔΣ Modulator solution?

And CC-MD if using MOSFET (for example: NTMFSC004N08MC) or GaN FET (for example: EPC2218), we are not aware of any device with isolation for the time being (if so, please let me know).

So based on the characteristics of CC-MD products, is it possible to meet the high resolution and accurate isolated phase current measurement?

Because we note that in the TIDA-00914 document, there is a particularly important statement "High-resolution, accurate, isolated phase current measurement is vital in industrial motor drive These applications include servo drives, robotics, machine tools, industrial manufacturing, and CNC machines."

We look forward to hearing from TI experts.

  • Oh, I'm sorry, I must add that the drive motor is a PMSM motor

  • Dear Kim,

    thank you for your interest in our TIDA-00914 reference design and isolated modulators. 

    I'd see two options for phase current sensing with 24V-60VDC servo drives depending on your isolation requirements.

    If you need isolation between your power stage and FPGA, the AMC1306M05 (+/-50mV input) or AMC1306M25  (+/-250mV input) would provide very accurate results as as shown with TIDA-00914. The AMC1306 has a very high CMTI (common mode transient immunity) of  100V/ns (typical), and quite well fits the high slew rate (dV/dt) seen when using GaN-FETs, which typically 10V/ns to 50V/ns.

    As mentioned we offer a 50mV or 250mV input voltage version. The 50mV version would allow you use a lower resistance shunt, if desired in your application.  

    Since the AMC1306 is powered from the high-side gate drive supply you can apply the AMC1306 circuit design from TIDA-00914 in a first step. A key difference is likely your high-side gate drive supply voltage, which may be 5V (or 12V) instead of 15V from the IGBT. If you do not have a high-side supply 
    the AMC3306M05 AMC3306M05 data sheet, product information and support | or AMC3306M25 would be a good option. It includes the an isolated DC/DC which powers the analog section of the modulator.

    If you open the replace the FPGA with our C2000 MCU like F28379D already includes the Sinc filters for delta-sigma modulators, otherwise you need to program on your FPGA. 

    If you do not need isolation between the power stage and your FPGA, you may also consider our INA241A (or INA240) ultraprecise current sense amplifiers with enhanced PWM rejection. Please refer to our reference design, whuch shows an example 48-60V GaN-FET inverter using the INA240 with a in-phase current shunt. In that example we use the C2000 MCU integrated ADC. I assume your FPGA does not have an ADC. In that case 
    you may use our non-isolated delta-sigma modulator AMC1035 for A/D conversion or our 12-bit 1MSPS SAR ADC like ADS7042 with SPI interface.

    Regarding GaN-FET drivers

    Have you looked at our 200V half-bridge gate drivers LMG1210 LMG1210 data sheet, product information and support | 
    The integrated dead time allows you to drive from a single PWM. In case you needed isolation you may use our multi-channel digital isolators, for example 
    our 6-channel isolator ISO6760, which fits 3-phase power stages. In case of the LMG1210 we'd use 3x PWM and 3x EN. 

    Please let me know when you have further questions. 


    Martin Staebler 

  • Thank you for your enthusiastic response, which made me experience TI's excellent service, and professionalism. I really like TI's devices. It is trustworthy. Let me describe to you in more detail our current environment and the considerations.

    Because our company has purchased a lot of Xilinx FPGA chips (the specific model is ZYNQ 7010) in the previous time, so far, the remaining quantity is about 5,000 pieces. So we don't want to waste it.

    The most important point is that the size of our PCB is very sensitive, its appearance is round, the outer diameter is only 90mm, and it has a hollow hole, the hole diameter is 40mm, so we can use very limited space, of course it has 2 layers, one layer is designed for the power board, one layer is designed for the control board, they are connected by B2B plug.

    These are some objective environmental factors.

    Then I will describe in detail the main confusion we encountered.

    Because we had little experience with isolated devices before that, we were not clear about the prerequisites for whether we needed to use them. For example, why do we need to use isolation devices and under what conditions? Of course, I probably understand that security may be a very important aspect, including the protection of the devices. However, due to the size sensitivity of the PCB, and cost control considerations, as we are currently accepting orders from customers in excess of 30,000 pieces.

    So my particular concern about whether or not to use isolated devices, in addition to the safety features, is whether or not there will be an impact on the accuracy of current sampling if isolated devices are not used? Resulting in inaccurate sampling?

    So based on this, we hope that TI experts, from a professional point of view for our portfolio selection (taking into account the size of our PCB, performance, cost), the more detailed the better, and can tell us why? After all, no one knows better than you the characteristics of TI products and the best use of scenarios.

    Thank you very much for the existence of such a great company as TI.

  • Dear Kim,

    Thank you for your feedback. If you system does not need isolation for electrical safety reasons, like we may see with 48Vdc-fed inverters, isolation
    can help to improve the common mode voltage and common mode voltage transient immunity (CMTI) of the current sensing. 

    When we use an isolated modulator like AMC1306 (SOIC-8), the isolated supply (typically the high-side gate drive supply and a 5V LDO)
    drives the input amplifier of the modulator. It therefore operate at a rather small voltage range, hence can be used with 230V-690V AC-fed systems, as well as 24-60V DC-fed systems. The AMC3306M25 or AMC3306M05 (SOIC-16) integrated an isolated DC/DC, hence do not need an isolated supply.

    Non-isolated amplifiers when powered with 3.3V or 5V and connected to an ADC, typically cannot operate at a common mode voltage range
    from 0V to 60V, as required for 60V DC-fed amplifiers. The INA240 and the later version INA241 have a common mode voltage range from -4V to 110V and in addition a very fast recovery from the transient PWM switching. The INA241 for example settles to 0.5% is just 1.5us after a PWM transient from 0V to 60V or
    vice versa. If you don’t intend to measure during the PWM switching time, the performance of the INA241 should be excellent too.  

    An overview is provided here: Selecting amplifiers for shunt-based current sensing in 3-phase motor drives:

    The INA241A (SOT-23-THN) with external 12-bit 1MSPS ADC ADS7042 (X2QFN (8)) would offer the significant smaller footprint vs. an isolated modulator.
    If you need higher than 12-bit the 14-bit 2.5MSPS ADS7056 (X2QFN (8)) would be an option.

    For details on the performance / accuracy I’d like to refer to again to the test results in the reference designs TIDA-00913 (INA240) and TIDA-00914 (AMC1306). If the accuracy of INA240 (INA241) meets your needs the INA241 + ADS7042 offers a significant smaller footprint solution.    

    From that you may decide which solution better fits your need.

    Does this answered your question?

    Martin Staebler