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MCT8316Z: MCT shows buck fault

Part Number: MCT8316Z

Hi there,

I have been working on a system which has multiple Motors and they communicate via CAN protocol and MCT8316Z (SPI version) is used for driving the motor. The system is working fine but the MCT shows buck fault and buck under voltage status bit is also set. While configuring the MCT we disable the buck regulator and neither are we using the FB_BK pin in our PCB (it is left unconnected). 

The values which we have written during configuration are :

Address    -      value

3              -        0x03

4              -        0x87

5              -        0x47

6             -         0x14

8              -        0x1

A             -         0x40

The values which I get during register read after configuring is:

0    -    48
1    -    0
2    -    90
3    -    3
4     -    86
5     -    47
6     -    14
7     -    30
8      -    1
9    -     0
a    -    40
b     -    0
c     -    0

Can this error cause any problem in the system? And what can be the cause of this error?

Thank you.

Jayam Srivastava

  • Hi Jayam,

    Are the buck components connected (LBK or RBK, and CBK)? They must be connected regardless if the the buck is disabled because at powerup because the device will report a buck undervoltage fault (BK_FLT), which is what you are seeing in the IC_Status_Register 0. 

    Thanks,
    Aaron

  • Attached is a picture of the concerned part of schematic. In this GND_BK and SW_BK are connected as they should be, just that the FBK connection which originates from the FB_BK and is further connected after R3 register with SW_BK is then connected nowhere. Will this cause any problem now also?

    If not, can this be the problem while improper assembly (soldering) only?

    Thank you.

  • Hi Jayam,

    Is RBK = 22ohm? The schematic is fine, FBK does not need to be connected to anywhere else in the circuit. Are the buck components placed close to the IC? If CBK is placed far, because it is only rated for 4V, it may be experiencing less rated capacitance. 

    A good way to confirm if a buck undervoltage fault is occurring is to monitor VM, FB_BK, and nFAULT. The buck should power up when VM > VM_UVLO. Below is normal powerup. 

    Thanks,
    Aaron