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SN65C1167E: Single ended PWM output coming out to be wrong

Sumanto Bhatacrya
Prodigy 20 points
Part Number: SN65C1167E
Other Parts Discussed in Thread: UCC21710

Tool/software:

Hello,

I am encountering an unexpected behavior with my current setup and would appreciate your input.

I’m using the SN65C1167ERGYR differential line receiver to convert a 5V differential PWM signal for interfacing with the UCC21710 gate driver. The differential PWM signal is a 5V, 10kHz pulse applied to pins 1 (A) and 2 (B) of the SN65C1167ERGYR. Please refer to the attached schematic for details.

The issue is that the single-ended output at pin 3 (R) remains stuck at a constant high level (5V), regardless of whether the differential PWM signal is present on the input lines or not.

Could you help me troubleshoot this behavior and point out any possible configuration or implementation errors I might be overlooking?



  • 0
    TI__Guru 72751 points

    Hi Sumanto,

    I don't see any major issues with the pinout of our device. Sometimes inductors on the differential side can cause issues but I wouldn't expect it to cause no R output. 

    Have you probed the RE# pin to verify it is being held to GND?

    Can you verify the device is soldered on properly and pin 1 is orientated properly? 

    Can you verify the Vcc is powered to the expected voltage?

    Do you have scopeshots of the A/B pins and the R output?  (preferably directly at the pin of the device)

    For the scopeshot, can you do a math function of A-B?

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 20 points

    Hello, 

    Thank you for taking your time to review our problem. 
    Below are my answers marked in BOLD. 

    The test below are done with no physical connection to the signal generator and the gate driver. 
    The EVAL board is just powered on with 12V and every other functions are working correctly. 


    Have you probed the RE# pin to verify it is being held to GND?  Yes 

    Can you verify the device is soldered on properly and pin 1 is orientated properly?  Yes . I resoldered a new device just to be sure. However no luck! 

    Can you verify the Vcc is powered to the expected voltage? yes we are measuring  clean 5,09 V at pin 12 and Pin 16

    Do you have scopeshots of the A/B pins and the R output?  (preferably directly at the pin of the device)  I am not providing any PWM to A and B, They are 0V. I also checked with multi and OSCi reference to GND. 


    Pin3 (1R) remains high under this circumstances. 

    The scopeshot of pin 3 is attached herewith. Seems like a continuous 5V signal. 

    What I also noticed that the floating pin 7 and 6 have a voltage of 2,5V referenced to GND. and pin 5 outputs a 5V. 

    Furthermore, I desoldered R55 connection to gate driver to see if the gate driver was doing anything stupid but 5V at pin 3 is remaining. 

    I would really appreciate your help in promptly resolving this problem as we need to bring this to production as early as possible. 

  • 0 in reply to Sumanto Bhatacrya
    Guru 316690 points

    0 V (or any other voltage) at both input pins is not a valid differential voltage. The A/B pins must have different voltages.

    Please specify exactly where that PWM signal comes from. What kind of differential driver does it use?

  • 0 in reply to Clemens Ladisch
    Prodigy 20 points

    Thank you for the answer. Yes you are right a negative differential voltage solved the problem. One followup question. does this mean when the microcontroller is off ( which in my case will generate the differential signal), the driver would in my used case give a high signal and which in turn turn on the MOSFET?  

  • +1 in reply to Sumanto Bhatacrya
    TI__Guru 72751 points

    Sumanto,

    The way the 1167 device works is if the differential input pins see the math of A-B become negative the R output goes low. If A-B is positive, the R output is held high.

    So if your MCU was powered off but the 1167 was powered on and the A/B pins were biased such that A-B was positive, then the R output would drive to Vcc. For an NFET, if the R output exceeds Vth of the NFET then you should expect the NFET to be turned on (either linear region of operation or saturation depending on the NFET's load).

    -Bobby