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DS90C031B: Recommended LVDS Products available for C2000 controller interface Expansion

CHOI SEUNG WON
Expert 1245 points
Part Number: DS90C031B
Other Parts Discussed in Thread: DS90C031, SN75LVDS9637, THVD2450, THVD2452V, THVD1452, THVD1450, THVD1428, THVD2429

Tool/software:

Dear TI

I reviewed the data on converting 3.3~5V digital signals to differential signals and interfacing them to C2000 series controllers in the sbaa607a.pdf data. I can't believe I'm looking at this data so late!

From my experience, I know that differential circuits are used for interfaces that operate at hundreds of MHz to hundreds of GHz for video signals, PCI, Ethernet, and synchronous dynamic memory.

Based on the sbaa607a.pdf data, I looked for LVDS parts that can be used for high-frequency PWM, digital output, and digital input. If the maximum frequency that can be driven from the GPIO of the C2000 is 50~100MHz and the power is used at 5V or 3.3V, I would like to ask if the products marked in blue in the block below can be used. Since I use the signal of the external connection connector of the C2000 as a voltage level of 5V, I searched under the 5V condition. I would like to ask if there are any additional products that TI experts can recommend.

Conditions: Electrical specifications that can be directly connected to C2000 (LVC~TTL 3.3V), PWM (important)/Communication (SPI, CAN, SCI, etc.)/GPIO signal expansion of C2000 product group, automotive grade (desired condition), 1~4 channel quantity, for digital circuits

  • 0
    TI__Genius 15321 points

    Hello,

    Would it be possible to share a block diagram of the intended application? 

    Can you let me know the intended input and output signal types? What is the signaling rate you desire?

    Do you have a preference for # of channels, and core supply voltage (5V or 3.3V or 1.8V)?

    Thank you, Amy

  • 0 in reply to Amy
    Expert 1245 points

    Dear Amy

    I use a single-ended voltage buffer when designing a controller using c2000. If I may add a little explanation, it is because I develop power electronics circuits, and I use 400V 800V high-voltage circuits, SiC, IGBT, etc. I think 5V is the minimum voltage that can be used in a noise-only circuit. Below 3.3V, it is very easy to be affected by noise in the 0~1200V range of automobiles/industry/batteries that I mainly deal with. 5V signals are also affected to some extent, but from experience, I think 5V components are relatively durable against external electrical noise.

    Even a few years ago, the systems I was developing were mostly products smaller than the internal A4 area. However, the output power is increasing from 7kW to 11kW, 22kW, 50kW, and even up to 200kW, so inevitably, larger power components are used, so the controller is designed to be modularized, and even if it is designed as an integrated controller, the distance between the controller and the power semiconductor increases significantly. Now, we have to consider up to 1~2 times the A3 area, and in this case, the pattern for the C2000 PWM signal becomes considerably long. If it is short, 10cm is possible, but if it is long, it is arranged up to 30~50cm.

    I am thinking of TI's LVDS application materials limited to the fields of video/RF/high-speed memory, etc., and I have never reviewed LVDS products as buffers.
    As shown in the reference image, I mainly use 3.3 to 5V, uni-directional, high-speed signal interfaces. I would like to receive recommendations for LVDS components that can be applied to such circuits. In fact, some circuits such as JTAG signals have been designed by replacing them with Isolated Digital Interface or RS422, but even if the insulation characteristics are obtained, the RS422 performance for increasing the cable length is very limited, so it could not operate at a maximum of 10MHz in the Jtage for C2000. If there is an LVDS suitable for automotive use or general signal use (such as general signal of digital signals, pwm, di, do, reset, etc.), I would like to receive a recommendation.

    Best regards, Choi

  • 0 in reply to CHOI SEUNG WON
    TI__Genius 15321 points

    Hi Choi,

    Thank you for all the detailed information. LVDS does have the benefit of noise cancellation due to the differential nature if that is of interest to you. 

    I have filtered through our portfolio and for 3.3-V to 5-V options: LVDS, M-LVDS & PECL ICs product selection | TI.com 

    You can further narrow the search by desired channel count and/or signaling rate.

    Here is a helpful post that I believe will relate to your application SN75LVDS9637: Noise immunity - Interface forum - Interface - TI E2E support forums

    Let me know if you have any other questions!

    Thank you, Amy

  • 0 in reply to Amy
    Expert 1245 points

    Dear Amy

    Wow, I just found out that RS485/422 interface and LVDS are comparable interfaces. I thought RS485/422 is a communication-only interface.

    But as you mentioned in the conversation, if RS485/422 can be used for signal extension of PWM, and higher noise margin and higher current output are possible, I have an additional question.

    As in my question, I am interested in a solution to extend high-speed interfaces such as PWM, SPI, DI, DO to C2000 microcontroller. In particular, PWM is a problem, and I need to review condition 1 below 100kHz, condition 2 100k~200kHz, and condition 3 above 200kHz~500kHz. Sadly, electric vehicles and environmental energy devices being developed recently use quite high frequencies.

    In the inverter field, the usual PFC topology operates at low frequencies of 10~20kHz. Currently, the vehicle is operating at 65kHz or higher, and 100~200kHz is also under development.

    In the converter field, OBC and LDC are already using 100~500kHz, and 200~300kHz is used on average.

    The power controlled by this system is at least 11kW~22kW, and in the case of high-capacity chargers, they are developed as 50~100kW modules, so they use quite a large space or area. As a result, the distance between the controller and each power device can be from tens of cm to meters.

    I am very interested in differential interface components that can transmit high-speed signals. I will review components such as SN75LVDS9637, DS90C031/032. And can you recommend components with RS485/422, 5V, and high-speed transmission specifications suitable for signal transmission such as PWM? I will review based on the recommended products.

    Best regards, Choi

  • 0 in reply to CHOI SEUNG WON
    TI__Genius 15321 points

    Hi Choi,

    Glad to hear that the article was helpful. I will loop in an RS485 expert to comment on RS485 solutions for your application.

    Thank you for the description. 

    Sincerely, 

    Amy

  • 0 in reply to CHOI SEUNG WON
    TI__Guru* 77791 points

    Hi Choi,

    RS485 is basically just a physical layer standard. The communication protocol can be anything that is unidirectional so you can input a PWM signal into any RS485 device. 

    Our modern day RS485 devices are basically 3 families. THVD14xx, THVD15xx, THVD24xx

    14xx is our general purpose devices and usually what we recommend to customers. (Usually this family can support both 3.3V and 5V but double check datasheet to be sure)

    15xx is a more cost competitive family set, usually with lower ESD and more restricted Vcc levels. (Normally Vcc=5V only)

    24xx is more robust with high fault protection and usually higher ESD/EFT/Surge ratings.

    We mainly recommend devices based on the customer's max datarate and if they need full duplex or half duplex. 

    For the fastest datarate half duplex, you can look at THVD2450 and full duplex THVD2452V (the V means it has separate Vio for down to 1.65V support)

    You basically have similar options if you look at the THVD14xx series, THVD1450 is half duplex and supports 50Mbps (25MHz) THVD1452 is the full duplex version. 

    If you wanted 20Mbps (10MHz) you could look at THVD1428 or THVD2429

    -Bobby

  • 0 in reply to BOBBY
    Expert 1245 points

    Dear Bobby

    I understand that RS485 is primarily an electronic component for the physical layer, typically used as a communication interface. However, I have not come across any application data specifically related to its use in digital input/output circuits, such as PWM or GPIO. For instance, most insulated and non-insulated gate driver components also accept inputs as digital signals. I have yet to see examples of circuits that directly receive differential signals to extend signal connection distances.

    Based on your explanation, I would like to request that TI develop application data for their gate driver components that utilize RS485, as well as gate driver components with RS485 differential interfaces.

    Best regards, Choi