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MCT8316A: How to protect the chip under overload conditions

Part Number: MCT8316A

Tool/software:

What is the best way to protect the chip from blowing up due to overload?

I was trying to establish the heatsink performance on our prototype board. The setup includes the prototype board connected to a 24 Volts 12 pole BLDC motor, speed =3600 rpm (no load) 3200 rpm (full load), continuous current rating of 8.2A.  The part is operated in close loop mode, The registers on the MCT8316 are set as follows: Close Loop1(0x86) = 0x0e3a0200, Fault Config1(0x92) = 0x78f43025, Fault Config2(0x94) = 0x7147a009, GD Config1(0xac) = 0x1c440000. I initially ran the test with CBC current limit set to 4A (Close Loop2 (0x88) = 0x02a6e4b0).  The speed was set to 100%, the motor reached the full speed under no load, then load was progressively increased. The motor stalled at about 3.2A I_Bus, CTL _FAULT register showed 0x80500000, the heatsink temperature was 118 F. I increased the CBC current limit to 6A (close loop 2 (0x88) = 0x02a6e4c8), Again the motor reached full speed under no load, the load was increased progressively until the bus current was about 5.6A, the speed dropped to about 1500 rpm. The motor ran for about 30 sec but never reached full speed, then the chip blew up. The control and gate drive fault status registers were constantly monitored but the CBC_ILIMIT, OCP, OT, OTW bits were never set. The chip never entered over current protection mode and shut itself down.     

The prototype board follows the layout example shown in fig 11-1 of section 11.2 of datasheet. The thermal pad on the chip is soldered to a ground plane on component side which is connected to the ground plane on the track side via a matrix of PTHs. The heatsink is mounted on the trackside.

  • Hello Suresh,

    Thanks for your question. Could you please give your complete register map settings? Also what is the frequency at which you are rading the FAULT status registers, are you also monitoring nFAULT?

    Regards,

    Sachin S

  • I changed CBC_ILIMIT_MODE to activate nFAULT when CBC_ILIMIT is crossed I can now see nFAULT being activated during CBC Current limit. Previously I was only monitoring gate_driver and Controller fault status registers using i2c interface about every 100 msec. Why the OTW and TSD bits were not set when the chip got damaged due to overload. Aren't both these bits supposed to stay latched until cleared by clear fault command? Why was the chip not protected by thermal shutdown?  I was not able to measure the chip temperature during the failure but since it blew up, I am assuming it must have crossed the warning and shut down thresholds. The OCP bit did not get triggered either.  

    What is the recommended way to protect the chip from getting damaged due to overload?

    I have attached a file giving all register settingRegSettings.pdf

  • Hello Suresh,

    Thanks for the details. Please give me time till 29 Jan to look at this.

    Regards,

    Sachin S

  • Hello Suresh,

    We had internal discussions regarding this issue, would you mind taking this conversation over e-mail to discuss the details?

    Thanks and regards,
    Sachin S

  • Hi Sachin,

    Sure, I have provided my personal email address, since any emails with attachments get deleted from the suresh_leley@dartcontrols.com address due to IT security policy, if possible, please use the address below, 

    suresh_leley@hotmail.com.

    One additional bit of information, the load was gradually increased while observing the 'Over current fault', 'Temperature warning' and 'Over Temperature shutdown' status bits when the chip blew up. As we discussed before the CBC current limit was not caught by the status register read code, probably the motor kept running for about 30 sec when the CBC current limit was active. This is partly confirmed as the observed motor rpm was much lower during this time.

    Thanks

    Suresh

  • Thanks Suresh,

    Will send you an e-mail regarding this. . 

    One additional bit of information, the load was gradually increased while observing the 'Over current fault', 'Temperature warning' and 'Over Temperature shutdown' status bits when the chip blew up. As we discussed before the CBC current limit was not caught by the status register read code, probably the motor kept running for about 30 sec when the CBC current limit was active. This is partly confirmed as the observed motor rpm was much lower during this time.

    Regards,

    Sachin S