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DRV8323-gate drive heat while motor running continuously & sometimes trips with voltage ,overcurrent

Part Number: DRV8323RS

Dear TI team ,

    We have designed our custom board using drv8323rs Bldc motor drive for running max 12000rpm ...and  used CSD19532KTT N-channel mosfet. for testing we have interfaced msp430(booster Drv8323 evm gui) with our custom board drv8323rs  Hall sensored project

intially motor didnt ran ,after referred smart gate driver document ..changed random step by step IDRIVEP and IDRIVEN  values as per Qgd/tr-source and Qgd/Tf -sink .motor start running and maximum 12000rpm also running.. but not as per calculated theoretical calculated values . 

Now we set IDRIVE_HS -0X03BF And IDRIVE_LS -0X06BF.. motor running was not proper sometimes ,gate driver trip with voltage fault and over current .. drv8323 starts heating up .. For example 6000rpm for half an hour running its trip... Please note mosfet not get heat... During testing without no load.. 

kindly guide us to calculate the IDRIVE values  as per attached mosfet datasheet and help me to clear this fault and reduce gate driver heating ...??

And also need to know reason of Drv8323 getting heat.. Because of IDrive settings  drv 8323 heating or any some other parameters need to change in hall based sensored code which Texas instrument provided..???

We initially we tested with launchpad msp430 and booster Drv8323rs evm gui . Successfully working fine . But we changed only mosfet in our custom board.. For no load gets heat... 

For another application with 2amps load with booster pack we facing above 50 degree heat in Drv8323 booster board itselff like Drv8323 and mosfet.. In the cases. Kindly guide us tunning parameter in given source code for bldc motor  ??? 

Thanks & Regards

ShriRam Jcsd19532ktt.pdf

  • Hi Ajay, 


    Thank you for posting in the BLDC forum! 

    It looks like the issue might be a result of your Idrive being too high. I would recommend trying a lower Idrive setting of 30mA rise time and 60mA fall time and see if that resolves your issues. If you can monitor the gate to source voltages and drain to source voltages that will help determine if the Idrive setting is too fast. If you see excessive ringing on the gate then that is a good indication that the Idrive is too high for your system to handle. 

     

    Regards,

     

    Anthony

  • Hi Anthony,

        Thanks for the reply , As per mosfet csd19532ktt datasheet IDRIVE>230mA(Qgd / trr)..

    Here with below attached IDRIVE settings , After changing Idrive values the gate driver heat not increases so much .

    IDRIVEP _HS-260mA

    IDRIVEN _HS-2000mA

    IDRIVEP _LS-260mA

    IDRIVEN _LS-2000mA

    TDRIVE -500ns

    DEAD TIME-40ns

    But we feel heat 15degree greater than ambient temperature or it is saturated ??..and also gate driver trips motor running every 5mins  and motor start running automatically.....some gate drive error occurred in drv8323 GUI log pane for your reference .

    kindly guide me to tune gate driver settings as per mosfet ,to clear the gate driver trips issue and gate driver heat..


    /* DRV8323 SPI REGISTER SETTINGS*/
    /* SPI_REG_02 : DRIVER CONTROL */
    #define RSVD        (0x00)         /*  */
    #define DIS_CPUV    (0x00)         /*  */
    #define DIS_GDF     (0x00)         /*  */
    #define OTW_REP     (0x00)         /*  */
    #define PWM_MODE    (0x00)         /*  */
    #define PWM_COM     (0x00)         /*  */
    #define PWM_DIR     (0x00)         /*  */
    #define COAST_BIT   (0x00)         /*  */
    #define BRAKE_BIT   (0x00)         /*  */
    #define CLR_FLT     (0x00)         /*  */

    /* SPI_REG_03 : GATE DRIVE HS */
    #define LOCK_BIT    (0x03)         /*  */
    #define IDRIVEP_HS  (0x08)         /*  */
    #define IDRIVEN_HS  (0x0f)         /*  */

    /* SPI_REG_04 : GATE DRIVE LS */
    #define CBC         (0x01)         /*  */
    #define TDRIVE      (0x04)         /*  */
    #define IDRIVEP_LS  (0x08)         /*  */
    #define IDRIVEN_LS  (0x0F)         /*  */

    /* SPI_REG_05 : OCP CONTROL */
    #define TRETRY      (0x00)         /*  */
    #define DEAD_TIME   (0x00)         /*  */
    #define OCP_MODE    (0x01)         /*  */
    #define OCP_DEG     (0x01)         /*  */
    #define VDS_LVL     (0x04)         /*  */

    /* SPI_REG_06 : CSA CONTROL */
    #define CSA_FET     (0x00)         /*  */
    #define VREF_DIV    (0x01)         /*  */
    #define LS_REF      (0x00)         /*  */
    #define CSA_GAIN    (0x01)         /*  */
    #define DIS_SEN     (0x00)         /*  */
    #define CSA_CAL_A   (0x00)         /*  */
    #define CSA_CAL_B   (0x00)         /*  */
    #define CSA_CAL_C   (0x00)         /*  */
    #define SEN_LVL     (0x03)         /*  */

    DRV8323GUI log pane:

    20-Feb-202112:59:26oneui: server: hwcomm: regread: [CSA Control @ 0x06] <= 579 (1613806165929)
    20-Feb-202112:59:26oneui: server: hwcomm: regread: [OCP Control @ 0x05] <= 83 (1613806165929)
    20-Feb-202112:59:26oneui: server: hwcomm: regread: [Gate Drive LS @ 0x04] <= 1167 (1613806165929)
    20-Feb-202112:59:26oneui: server: hwcomm: regread: [Gate Drive HS @ 0x03] <= 911 (1613806165929)
    20-Feb-202112:59:26oneui: server: hwcomm: regread: [Driver Control @ 0x02] <= 0 (1613806165929)
    20-Feb-202112:59:26oneui: server: hwcomm: regread: [VGS Status 2 @ 0x01] <= 0 (1613806165929)
    20-Feb-202112:59:25oneui: server: hwcomm: regread: [Fault Status 1 @ 0x00] <= 0 (1613806165929)


    Regards,

    shriram J

  • Hi Shriram J,

     

    Thank you for your response! The IDRIVE setting for your MOSFET fall time is really high. I would recommend significantly reducing it. Could you provide waveforms showing the gate to source turn on and turn off of the high and low side MOSFETs of one of the phases? Additionally, could you provide waveforms showing the drain to source voltage of the high side and low side MOSFETs of one of the phases? If there is significant oscillation during the turn on and turn off of the MOSFET then that is an indication that the IDRIVE settings are still too high. many designers consider 200ns/100ns turn on/turn off time to be fast, and depending on the layout of the design that could still be too fast for your particular design.

    What fault are you getting when the motor driver trips? This can be determined by reading the bits in Fault Status registers 1 and 2.

    Regards,

    Anthony 

  • Hi Anthony,

    Thanks for the reply, Here with we have attached High and low side mosfet waveform for your reference ..,

    1.Motor switching frequency -20KHz for 10000 rpm

    Now attached waveform with 50% of switching frequency -10KHz of PHASE A

    DRAIN-SOURCE -HS

    GATE- SOURCE -HIGH SIDE

    DRAIN-SOURCE LOW SIDE

    GATE-SOURCE LOW SIDE

    Trapezoidal waveform :300HZ electrical speed max for 10000 RPM

    2.Kindly, mention Tdrive or Dead time what value that you want me change ?? the wave form are took by this settings that I have mentioned already

    DRIVEP _HS-260mA

    IDRIVEN _HS-2000mA

    IDRIVEP _LS-260mA

    IDRIVEN _LS-2000mA

    TDRIVE -500ns

    DEAD TIME-40ns

    3.We have got some error value from Log pane drv8323GUI ,kindly guide us how to check those values and changes settings as per our design ..

    how to find this values??

    24-Feb-2021
    15:36:26
    oneui: server: hwcomm: regread: [Gate Drive LS @ 0x04] <= 1280 (1614161185856)
    24-Feb-2021
    15:36:25
    oneui: server: hwcomm: regread: [Gate Drive HS @ 0x03] <= 911 (1614161185856)
    24-Feb-2021
    15:36:25
    oneui: server: hwcomm: regread: [Driver Control @ 0x02] <= 0 (1614161185856)
    24-Feb-2021
    15:36:25
    oneui: server: hwcomm: regread: [VGS Status 2 @ 0x01] <= 0 (1614161185856)
    24-Feb-2021
    15:36:25
    oneui: server: hwcomm: regread: [Fault Status 1 @ 0x00] <= 0 (1614161185856)
    24-Feb-2021
    15:35:35
    oneui: server: hwcomm: regread: [CSA Control @ 0x06] <= 646 (1614161134929)
    24-Feb-2021
    15:35:35
    oneui: server: hwcomm: regread: [OCP Control @ 0x05] <= 84 (1614161134929)
    24-Feb-2021
    15:35:35
    oneui: server: hwcomm: regread: [Gate Drive LS @ 0x04] <= 1280 (1614161134929)
    24-Feb-2021
    15:35:35
    oneui: server: hwcomm: regread: [Gate Drive HS @ 0x03] <= 911 (1614161134929)
    Thanks& Regards
    shriram J

  • Hi Anthony,

             Thank for the response , As per your suggestion run motor with  I DRIVE settings 230mA/560mA ..now gate driver trip motor every 10mins and THENm otor heat & gate driver heat got saturated ..kindly guide me to sort out this issue.

    Thanks& regards

    Shriram J

  • Hi Shiriam J,

     

    Thank you for your reply!

     

    The errors that you are seeing in the log pane aren’t actually errors, but rather they are a description of the changes that have been made to the registers. For instance:

    24-Feb-21  |  15:36:25 |  oneui: server: hwcomm: regread: [Gate Drive HS @ 0x03] <= 911 (1614161185856)

     

    This means that register 0x03 (which is the HS Gate Drive Settings) has been changed to 911 (base 10) which is equal to 011  1000   1111 (base 2) Which means that the IDRIVEN_HS has been changed to 1111b (or 2000mA), IDRIVEP_HS has been changed to 1000b (or 260mA), and the Lock setting is 011b (which unlocks the registers and allows you to change their value)

     

    The same logic can be applied to all the messages in the log pane to identify the changes that were made to the registers.

     

    In the waveforms that you included I noticed there was a lot of parasitic ringing that occurred during the switching on and off of the MOSFETs. This can cause the driver to heat up and can also cause damage to the motor driver since it can cause the Absolute Maximum values of the driver to be exceeded. If the Idrive settings are too high for your design then that could be one source of the ringing that you are seeing. You mentioned that you later lowered the Idrive settings to 230mA/560mA and it seemed like that improved the length of time before the device would trip. Could you provide a scope plot showing the gate to ground signal on both the high and low side MOSFETs while using an Idrive setting of 230mA/560mA? Can you also mark on the oscilloscope the time it takes for the gate voltage to go from the off state until it is fully on (this is the rise time of the MOSFET)? Can you repeat the same test using an Idrive setting of IDRIVEP_HS = 30mA, IDRIVEN_HS = 60mA, IDRIVEP_LS = 30mA, IDRIVEN_HS= 60mA? The register to change the IDRIVE_HS is register 0x03 and the register to change the IDRIVE_LS is register 0x04. I want to start out with a really low IDRIVE (30mA/60mA) as a test to see how it effects the operation of the device. If that solves the issue of the driver overheating/tripping, as well as solves the issue of the ringing during the switching of the MOSFETs, then we can try to slowly increase the Idrive until we start to see the ringing again during the switching of the MOSFETs.

    You mentioned that the deadtime you are using is 40ns, however the lowest deadtime that this device supports is 50ns (see register 0x05 bits 9-8). Did you mean 400ns?

    A TDRIVE of 500ns is fine for now, but we may want to adjust that later on if that starts to cause issues.

    Can you provide a screenshot showing the values you have entered into the registers on the DRV8323GUI?

    Regards,

     

    Anthony

  • Hi Anthony,

               Thanks for your valuable support, As per your suggestion I drive setting  30mA/60mA..we have ran motor for about 2hours 45minutes .. gate driver  didn't trips the motor ..it is running continuously  ..drv8323 gate driver settings attached below for your kind reference . Next issue gate driver and motor getting hot gradually ,increases 20degree greater than ambient  temperature

    I DRIVE HS -30mA/60mA

    I DRIVE LS -30mA/60mA

    T DRIVE      -500ns

    DEAD TIME -200ns

    /* DRV8323 SPI REGISTER SETTINGS*/
    /* SPI_REG_02 : DRIVER CONTROL */
    #define RSVD        (0x00)         /*  */
    #define DIS_CPUV    (0x00)         /*  */
    #define DIS_GDF     (0x00)         /*  */
    #define OTW_REP     (0x00)         /*  */
    #define PWM_MODE    (0x00)         /*  */
    #define PWM_COM     (0x00)         /*  */
    #define PWM_DIR     (0x00)         /*  */
    #define COAST_BIT   (0x00)         /*  */
    #define BRAKE_BIT   (0x00)         /*  */
    #define CLR_FLT     (0x00)         /*  */

    /* SPI_REG_03 : GATE DRIVE HS */
    #define LOCK_BIT    (0x03)         /*  */
    #define IDRIVEP_HS  (0x01)         /*  */
    #define IDRIVEN_HS  (0x01)         /*  */

    /* SPI_REG_04 : GATE DRIVE LS */
    #define CBC         (0x01)         /*  */
    #define TDRIVE      (0x00)         /*  */
    #define IDRIVEP_LS  (0x01)         /*  */
    #define IDRIVEN_LS  (0x01)         /*  */

    /* SPI_REG_05 : OCP CONTROL */
    #define TRETRY      (0x00)         /*  */
    #define DEAD_TIME   (0x02)         /*  */
    #define OCP_MODE    (0x01)         /*  */
    #define OCP_DEG     (0x01)         /*  */
    #define VDS_LVL     (0x04)         /*  */

    /* SPI_REG_06 : CSA CONTROL */
    #define CSA_FET     (0x00)         /*  */
    #define VREF_DIV    (0x01)         /*  */
    #define LS_REF      (0x00)         /*  */
    #define CSA_GAIN    (0x01)         /*  */
    #define DIS_SEN     (0x00)         /*  */
    #define CSA_CAL_A   (0x00)         /*  */
    #define CSA_CAL_B   (0x00)         /*  */
    #define CSA_CAL_C   (0x00)         /*  */
    #define SEN_LVL     (0x03)         /*  */

    Register settings :

    Waveform:

    1.How can we decide IDRIVE as low as value ?? kindly clear us ..as we thought that IDRIVE >Qgd/Trise  OR  Qgd/Tfall

    2.can we take test with 10mA/20mA??

    3.kindly clear us this way we finf Tdrive >QGD/Ig

    Kindly ,guide me  sort out and reduce ate driver heat & motor heat...

    Thanks & Regards

    Shriram J

  • Hi Shiram J,

     

    I am glad to hear that the change in IDRIVE was able to resolve the tripping issue! You can definitely try using the 10mA/20mA Idrive setting to see how it performs.

    Rise time is the time it takes for the MOSFET to go from the off state to fully on state. Fall time is the time it takes for the MOSFET to go from the fully on state to the off state. The formulas:

    • Idrive = Qgd/Trise and
    • Idrive = Qgd/Tfall


    are a rough approximation to select the appropriate Idrive for your system. Typically, a 200ns/100ns rise time/fall time is considered fairly fast by many designers, and depending on the board design (trace inductance, trace length, ect.) your particular design may or may not be able to handle that fast of switching times.

    If you wanted to target a rise/fall time of 200ns/100ns, and the Qgd of your MOSFET is 5.6nC, then an Idrive setting of

    • 5.6nC/200ns = 28mA would approximately achieve a 200ns turn on time (the closest available setting is 30mA, which would achieve a rise time of approximately 5.6nC/30mA = about 187nS, which is a little bit faster than your target of 200ns)

      and an Idrive setting of

    • 5.6nC/100ns = 56mA would approximately achieve a 100ns fall time (the closest available setting is 60mA, which would achieve a fall time of approximately 5.6nC/60mA = 93.3ns, which is a little faster than your target 100ns fall time).

    There are several tradeoffs you have to consider when choosing the desired MOSFET rise and fall times. A faster MOSFET rise and fall time means that the MOSFETs turn on or off quicker, so that results in lower MOSFET switching losses (When your transistor is only partly on there is higher power consumption). However, if your rise and fall time is too fast, you will cause parasitic ringing on the gate and source of the MOSFETs, which can cause excessive heating and damage to the driver and/or the MOSFETs. The best way to tell if the rise/fall time is too fast for your system is to look for excessive parasitic ringing by monitoring the gate to ground voltage for both high side and low side MOSFETs, as well as the source to ground voltage of the high side and low side MOSFETs. This ringing will typically be seen as the MOSFETs are turned on or turned off.

    Even though the device is not tripping with an Idrive of 30mA/60mA, I would still monitor the gate to ground voltage to make sure there isn’t any excessive ringing on the gates. You can also do the same with monitoring the source to ground voltage for ringing. You can also try various Idrive settings to find the one that works best for your design, making sure to monitor the gate voltage for ringing. 

    The Tdrive is a setting that is used as a safety feature. One of the purposes of the Tdrive setting is to monitor to see if the gate of one of the MOSFETs is stuck on or off. If you use a Tdrive setting of 500ns, and then a command is given to change the state of a MOSFET (either turn it on or off), if the MOSFET hasn’t changed to the desired state at the end of 500ns, then the driver will report a fault and shut down the driver. You want to make sure that the Tdrive time is greater than the expected time it takes for the MOSFET to turn on or off. If you expect the MOSFET to have a 200ns/100ns rise/fall time, then a 500ns Tdrive time would allow for sufficient time for the MOSFET to turn on without triggering an undesired fault. For more information on Tdrive you can read sections 8.3.6.5 and 8.3.1.4.2 in the datasheet.

    I will get back to you on Monday regarding the driver heating. 

    Regards,

    Anthony 

  • Anthony,

        Thanks for the reply , we have tested with I Drive settings  10mA/20mA but gate drive trip as same like  before ...motor running fine for about 6 hours    with 30/60mA settings  as per the calculation .

    For parasitic ringing problem attached waveform for your kind reference ,it may sort out our next issue of motor heat and gate driver heat.kindly reference give us an solution .

    ground to source :

    ground to gate:

    GUI Settings:

    Guide me to sort out motor heat and gate driver issue ..

    Regards

    shriram J

  • Anthony,

        Thanks for the reply , we have tested with I Drive settings  10mA/20mA but gate drive trip as same like  before ...motor running fine for about 6 hours    with 30/60mA settings  as per the calculation .

    For parasitic ringing problem attached waveform for your kind reference ,it may sort out our next issue of motor heat and gate driver heat.kindly reference give us an solution .

    ground to source :

    ground to gate:

    GUI Settings:

    Guide me to sort out motor heat and gate driver issue ..

    Regards

    shriram J

  • Anthony,

        Thanks for the reply , we have tested with I Drive settings  10mA/20mA but gate drive trip as same like  before ...motor running fine for about 6 hours    with 30/60mA settings  as per the calculation .

    For parasitic ringing problem attached waveform for your kind reference ,it may sort out our next issue of motor heat and gate driver heat.kindly reference give us an solution .

    ground to source :

    ground to gate:

    GUI Settings:

    Guide me to sort out motor heat and gate driver issue ..

    Regards

    shriram J

  • Anthony,

        Thanks for the reply , we have tested with I Drive settings  10mA/20mA but gate drive trip as same like  before ...motor running fine for about 6 hours    with 30/60mA settings  as per the calculation .

    For parasitic ringing problem attached waveform for your kind reference ,it may sort out our next issue of motor heat and gate driver heat.kindly reference give us an solution .

    ground to source :

    ground to gate:

    GUI Settings:

    Guide me to sort out motor heat and gate driver issue ..

    Regards

    shriram J

  • Hi Shriram J,

    I will get back to you tomorrow to respond to your questions.

    Regards,

    Anthony 

  • Hi Shiriam J,

     

    Thank you for your response. In order to be able to determine if there is significant ringing on the gates and/or sources of the MOSFETs we will need to see a zoomed in picture of 1 or 2 pulses of the gate to ground and source to ground signals. Could you provide the zoomed in ground to source and ground to gate tests for both the high and low side MOSFETs? The oscilloscope plots you included shows many on and off switching events, so it is difficult to exactly see what is going on with ringing and voltage spikes because it is too zoomed out.

     

    Do you have any components attached to the DVDD pin (besides the DVDD capacitor)? If you don’t then if the device is heating up 20 degrees hotter than ambient that seems hotter than I would expect. Is the 20 degrees temp increase coming from the DRV8323, or is it coming from the MOSFETs? If it is the MOSFETs that are getting 20 degrees hotter than ambient then I wouldn’t be concerned about that since they consume more power than the DRV. But if the DRV is heating up to 20 degrees above ambient and you do not have any load attached to DVDD, then there is some concern that the device is heating up too hot.

     

    You mentioned that you get a fault when you use the 10mA/20mA IDRIVE setting. One possibility for that issue is because the MOSFETs may not have time to fully turn on during the TDRIVE time since the IDRIVE could be too low. One way to verify this is to use the 10mA/20mA setting and adjust the TDRIVE setting to 1000ns instead of 500ns to see if it no longer gives a fault. Just to confirm: you can operate the device using an IDRIVE setting of 30mA/60mA and you don’t get any faults and can run it for long periods of time without the driver shutting down?

     

    Regards,

     

    Anthony

  • Hi Anthony,

    Thanks for the response

    1.we have not connected any load for DVDD pins ..as it is in the drv8323RsEVM schematic it is grounded with capacitor

    2.As per your suggestion, we have tested with I-drive settings-10/20mA and T drive 1000ns , motor running continuously without any  gate driver trips .

    we found that gate driver heat reduced  as much before 20/30mA setting ...but motor heat increases (settings-10/20mA)... too high .

    kingly suggest us to reduce motor heat ....

    3.please find waveform below with respect to last reply. for your kind reference :

    1.ground to gate

    2.Ground to source:

    Kindly ,guide us to reduce motor heat ..

    we  feel this conversation can be in private ?could you make this form in private mode .

    Thanks & Regards

    Shriram J

  • Hi Shriram J,

     

    Thank you for your response! E2E is a public forum, and unfortunately there isn’t any setting that allows us to make the thread private. If you want this discussion to continue privately you can message me and we can continue the discussion via email.

     

    The fact that the longer Tdrive setting allows the motor to operate properly with 10mA/20mA Idrive suggests that the 10mA/20mA Idrive setting is too low and results in a long time for the MOSFETs to fully turn on. This will result in higher power dissipation across the MOSFETs since they are operating in the linear region for a longer period of time.

     

    For the waveforms that you provided, was that with an Idrive of 30mA/60mA? Or was that with an Idrive of 10mA/20mA?

     

    The waveforms that you provided look good. There is some ringing on the source (about 2-3V), but it isn’t too much of a concern since it is still well below the absolute maximum rating of the device.  

     

    I have a few questions for you:

    1. You mentioned that the heating of the driver was reduced when you used an Idrive of 10mA/20mA compared to when you were using an Idrive setting of 30mA/60mA. What is the temperature increase of the DRV during operation using the Idrive setting of 10mA/20mA? What is the temperature increase of the DRV during operation using the Idrive setting of 30mA/60mA?
    2. What is the temperature increase of the MOSFETs during operation?
    3. What is the temperature increase of the motor during operation?
    4. What is the rated current for your motor? What is the resistance of the motor you are using? How much current is your motor using during normal operation?

     

    Regards,

     

    Anthony

     

  • Hi Anthony ,

    Thanks for your reply, we have sent you wave forms of 30/60mA I drive settings in the  last forum ..Here with this attached 10/20mA waveform for your kind reference .

    GATE TO GROUND:10/20 I drive

    SOURCE TO GROUND-10/20mA

    *************

    As per last reply ,you have discussed  some questions..so that we have took temperature study for both the settings of I drive 10/20mA and 30/60mA comparison Kindly refer ..Here with attached Excel document kindly find out and guide me sort out the motor heat issue .

    drv8323-Temperature Study.xlsx

    No load current :400mA for max 10000rpm

    MOTOR SPECIFICATIONS:

    NO.OF.POLES -4

    RATED SPEED -12000RPM

    LINE RESISTANCE -1.5ohm

    PEAK CURRENT -5.5A

    LINE INDUCTANCE -4.5mH

    VOLTAGE -24V

    RATED TORQUE-0.11

    PEAK TORQUE-0.35

    BACK EMF-3.8Vrms/K rpm

    Guide me to sort out the motor heat issue ..

    Thanks&Regards

    Shriram J

  • Hi Shriram J,

    Thank you for your response! I had a discussion with a coworker today regarding your issue and will be responding tomorrow.

    Regards,

    Anthony 

  • Hi Shriram J,

    After looking over the data you provided it looks like the current rating of the motor may be exceeded which is causing it to overheat. It looks like the duty cycle that you are operating at is about 80%, so with a 24V supply that creates an average voltage of about 19.2V across the motor windings. If the motor resistance is 1.5 ohms x 2, then the average current through the motor is 6.4A which would exceed the current rating of the motor and cause motor heating. If you would like to check this, you can test the voltage across one of the sense resistors on one of the phases and calculate the current.  The reason that you might be only seeing 400mA drawn from the supply is that the current recirculates through the FETs and through the motor which means that it doesn’t have to draw as much current from the supply.

     

    A few possibilities as to why the motor is only spinning at 10000 RPM despite using over 6A of current:

    1. You may want to double check to make sure there isn’t any unexpected load on the motor
    2. The motor might not be spinning normally due to damage from the ratings of the motor being exceeded. That could possibly cause the motor to not be able to get up to speed well.
    3. If the algorithm is commutating the motor inefficiently, this would result in higher current needed to spin at a certain speed.

    I would recommend replacing the motor just in case the one you are currently using is damaged (if you have another one), and also reducing the duty cycle of your PWM so that the current rating of the motor is not exceeded to see if that solves your motor heating issues.

     

    Would you mind providing your layout for us to look at? You can send it privately if you want. I want to check the layout to see if there are any obvious issues that could contribute to heating.

     

    Regards,

     

    Anthony

  • Hi Anthony,

      Thanks for the response , we are looking at mentioned points of your last reply ..will respond by  tomorrow ..

    Thanks & Regards

    Shriram J

  • Hi Shiram,

    Electric motor losses (BLDC motor losses as well), the major ones are:

    1. copper losses, proportional to I^2R. The higher the motor load the higher the losses.

    Additionally resistance of motor windings rises with its temperature. Because of these losses you can run safely

    motor at nominal current (which is around 5.5x 0.11/0.35 = 1.73A) continuously or for short period of time at currents

    up to 5.5A, the more motor current is over its nominal value the shorter time you can run it safely. All that is valid for low speeds,

    because at high speeds another losses start to play their role.

    2. iron losses, generally they rises as speed goes up and frequency of changes of magnetic field in stator core rises (with speed).

    They also depend on motor design like magnetic core material, its lamination etc. At speeds around 10000rpm they can be significant

    even for motor with only 4 poles. 

    3. Mechanical losses, they rises with speed as well. If motor has bearings not designed for high speeds these can be quite high at 10000rpm.

    There might be possibility of lowering first two types of losses with help of vector control (FOC), but it will not be a very significant difference

    and subject is quite complex. With vector control you can also get some increase of speed for nominal load (some smart vector control technique) and much higher speeds for small loads (field weakening technique). If you are interested you can find on youtube the best series of videos I have ever come across, it is "Teaching old motors new tricks" by Dave Wilson (TI).

    TI also offers some evalkits for BLDC motors with FOC software packages.

    If motor is damaged the losses can be significantly higher.

    Coming back to your motor running unloaded at 10000rpm, the losses that heats that motor by around 20C probably are mostly

    iron and mechanical losses and can be quite normal for that motor.

     

    Regards,

    Grzegorz

  • Just a small correction.

    It should be possible to run a motor continuously (if motor is designed for continuous duty)  up to its nominal speed 

    at rated current. Then the sum of all losses should not cause motor overheating.

    Grzegorz

  • Hi Anthony,

    The motor current is limited not only by BEMF and winding resistance but also by winding inductance and motor current

    at 10000 rpm probably is much lower than 6A, the best way to check it is to measure it with current probe.

    As for reason for the motor not being able to spin faster than 10000rpm I agree with all 3 points.

    If last three oscillograms were made at 10000rpm I would suspect PWM duty cycle is the limiting factor. Increasing

    PWM duty cycle up to 100% should spin that motor faster, it is just my guess.

    Regards,

    Grzegorz

  • Hi Anthony,

             Thanks for the reply, yes we are running with 20Khz switching frequency  80% of duty cycle 19.2 voltage ...we didn't think the motor is running above rated current  measured with clamp meter  shows only 0.4A.

    As per your suggestion measure voltage across sense resistor ..we don't have propagation to measure  voltage across 7milli ohm shunt resistor and  Need to measure 400mA in 0.007reistor ..voltage will be in Milli volt right ? will respond you by tomorrow .

      

    Thanks & Regards

    Shriram J

  • Hi Anthony,

           Kindly share mail id , will send our schematic for your reference.

    Thanks & Regards

    Shriram J

  • Hi Shriram,

    Motor current analysis is very important in motor driver design process. It is very difficult to measure and analyze current on sense

    resistor because of switching noise and current may be recirculated sometimes outside sense resistors unless someone uses

    sense resistors inline with motor phases. Much better solution is oscilloscope current clamp, even low cost (around 50Euro) like

    this one.

    http://www.hantek.com/products/detail/77

    To increase speed I would try to increase PWM duty cycle.

    Regards,

    Grzegorz

  • Hi Shriram J,

    I will message you soon with that information.

    Regards,

    Anthony

  • Hi Grzegorz,

     

    Thanks for your input! I agree that the inductance of the motor will somewhat limit the motor current, but there is still the possibility in this case that the average current over time will exceed the rating of the motor. Hopefully further testing will allow us to get a better idea of how much current is flowing in the coils.

     

    Although increasing the duty cycle would make the motor spin faster, I don't think it wouldn’t be a good idea to increase the duty cycle since we are already experiencing a lot of heating, and a higher duty cycle would only increase that issue. The heating seems to indicate that there is a bigger issue that is going on that is causing a higher than expected duty cycle to be necessary to achieve a given motor speed.

     

    Regards,

     

    Anthony

  • Hi Shriram J,

     

    Even though you are seeing only 0.4A being drawn from the power supply, there still can be a much higher current circulating through the motor due to the inductance of the motor causing the current to recirculate through the phases. The results of testing the voltage across the sense resistor will help us get a better idea about how much current is flowing in the motor.

     

    You are correct, the voltage that would be sensed across the sense resistor would be in the millivolt range. If it is possible to get an oscilloscope plot of the voltage that would be best. One option that may make it easier is to measure the output of one of the integrated sense amplifiers (SOx pins). We can use the gain setting that you programmed (based on the CSA_GAIN register value) to calculate the voltage across the shunt resistor and thus the current through the phase.

     

    Another test you could perform is outlined below:

        1. Adjust the gain of the current sense amplifiers to 20V/V by writing 10b to bits 7-6 of the CSA Control Register.

        2. Adjust the sense OCP (Over Current Protection) threshold to 0.75V by writing 10b to bits 1-0 of the CSA control Register.

        3. Since you are using a 7miliohm resistor, the overcurrent protection feature would trip when the current through the sense resistor reaches about 5.357A (since 5.357A*0.007ohms = 0.0375V, and 0.0375V*20V/V = 0.75V

        4. If this test causes the Overcurrent protection feature to trip then that would indicate that the current through the motor is exceeding 5.357A, and would be a good indicator to see if the heating is a result of the current being too high through the motor.

    Would you be able to share the motor part number so I can look at the datasheet?

     

    Regards,

    Anthony

  • Hi Anthony,

         Thanks for the response, As per your suggestion we have changed CSA gain  20V/V and sense level -0.75v for both the I DRIVE Settings 10mA/20mA & 30mA/60mA ..and the motor running continuously without any gate driver trips or fault ..it shows motor heat is not result of current being high though the motor .

    we have noticed that after changing the CSA gain and sense level motor heat and gate driver heat is too high ..as compared before.

    MOTOR PART NUMBER : FL57BLS54.005

    Special motor : 12000 rpm

    Kindly give me solution to reduce motor heat ..

    Thanks & Regards

    Shriram J

  • Hi Shriram J, 

    Is the 5.5A rating on the motor the peak current rating? or is that the continuous current rating? If it is 5.5A peak current then would you be able to check what the continuous current rating is? Peak current is only in reference to the amount of current that the motor can handle for a short duration of time. Even if the motor isn't operating at the peak current of the motor, there still can be overheating that occurs if it is operating above the continuous current rating.

    Even though the test didn't result in the tripping of a fault I would still like to have a more accurate idea of how much current is flowing in the motor. If you could measure the output of one of the integrated sense amplifiers (SOx pins) using an oscilloscope that would be helpful. I would also recommend using a new motor with a 60 percent duty cycle to see if some of the issues are a result of the old motor being damaged. 

    How much extra heating did you see in the motor driver as a result of increasing the CSA gain to 20V/V? 

    Regards,

    Anthony

  • Hi Shriram J, 

    I am going to close this thread since we have been communicating offline regarding the layout changes. Once you have made the changes to the layout feel free to reach out to me and we can review it again. If you have any related questions feel free to use the "ask a related question" button and create a new thread.

    Regards,

    Anthony