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DRV8350S-EVM: Question for SLA

Annie Liu
Genius 10295 points
Part Number: DRV8350S-EVM

Hi Team,

SLA will be compared with GLA inside the IC, but SLA is connected to GND. SLA is all 0V, why should SLA be FEEDBACK?

Thanks,

Annie

  • 0
    TI__Mastermind 26046 points

    Hi Annie,

    I am confused by the question. Are you talking about the current configuration of the DRV8350S-EVM?

    SLA is tied to the rest of the low-side sources of the LS MOSFET, then all go a single shunt amplifier. SLA will be close to 0V, but the main purpose is to sense VDS and VGS voltages, as well as provide a return path for the gate drive sink current. SLA should be connected near the source of phase A's low-side MOSFET source. 


    Thanks,
    Aaron

  • 0 in reply to Aaron Barrera
    TI__Genius 10295 points

    Hi Aaron,

    He doesn't talk about the current configuration of the DRV8350S-EVM. Hw wants to discuss the application of DRV8350S.

    Question 1:

    Aaron Barrera said:
    as well as provide a return path for the gate drive sink current

    If the gate drive current is 1A, the SLA will also have a current of 1A. SLA is also used to detect whether there is an output current of 1A. Is it correct?

    Question 2:

    What is the function of the circuit outlined in red？

    Thanks,

    Annie

  • 0 in reply to Annie Liu
    TI__Mastermind 26046 points

    Hi Annie,

    1. You will not see the 1-A current flow from GLA to SLA because this current is instantaneous and significantly smaller than continuous phase motor current.  IDRIVE are instant peak source and sink gate currents to turn MOSFETs on and off. When motor current flows through the 1/2 bridges into SLA, SLB, and SLC, the continuous current present will be motor current rippling at the PWM frequency. 

    2. The circuit outlined in red is an external current sense amplifier (CSA). What is happening is that all low-side MOSFET's sources are tied together on the EVM with a big copper area (SLA = SLB = SLC). Motor current flows through the shunt resistor R75 and results in a difference in voltage (Ishunt * Rshunt) between SP and SN. The inputs are fed into the external current sense amplifier, which has a fixed gain to bump up the output voltage into a usuable ADC voltage between 0 and 3.3V that is proportional to the motor current. This is used to help detect overcurrent conditions in software.

    Thanks,
    Aaron

  • 0 in reply to Aaron Barrera
    TI__Genius 10295 points

    Hi Aaron,

    VM input is 12V, VDRIN input is 48V. There is no problem when the customer uses 10A current to drive the Motor. When the current is increased to 35A, the DRV8350S will burn out. 

    There are two types of burning:

    1. GLX output is 5V (correctly should be 12V), but after disconnecting the connection between SLX and MOS, GLX will return to 12V

    2. GHX outputs are all 48V (correctly should be 60V)

    How to check the cause of this failure? 

    GLX output is 5V, and GHX output is 48V, does it mean that it has been burned?

     

    Thanks,

    Annie

  • 0 in reply to Annie Liu
    TI__Mastermind 26046 points

    Hi Annie,

    The EVM is rated for only up to 15-A use. MOSFETs are rated up to 17-A peak. It is likely that the low side MOSFET is damaged, which can cause the GLx to not turn on the gate properly (5V instead of 12V). 

    Can the customer replace the MOSFETs onboard the EVM with higher rated MOSFETs and see if the issue goes away? 

    Also ensure when MOSFETs are used, use a low IDRIVE setting to switch the gates slower. 

    Thanks,
    Aaron

  • 0 in reply to Aaron Barrera
    TI__Genius 10295 points

    Hi Aaron,

    Sorry for the misunderstanding. The customer is not using the DRV8350S-EVM, but the problem that occurs when they use the DRV8350S to make a circuit by themselves. 

    The MOS used by the customer is 300A, and the MOS is not burned. The one that got burned was the DRV8350S. 

    May I ask if the GLX output is 5V, and the GHX output is 48V, does it mean that it has been burned? When using a MOSFET, IDRIVE is a fixed setting of 600mA to switch the gate. But when the current increases to 35A, the DRV8350S burns out.

    Thanks,

    Annie

  • 0 in reply to Annie Liu
    TI__Mastermind 26046 points

    Hi Annie,

    Best way to confirm if there is pin damage is to measure impedance of the damaged pin(s) to GND of the bad unit and compare to the good unit. If the impedance is different, or if there is an open or short to GND, then there is likely damage. 

    GLx should output ~10V when INLx = 1 and GHx should output SHx + VCP when INHx = 1. Please confirm VCP is not damaged (5V instead of 10-12V). If there is damage, it is likely the DRV8350S got burned at too high of an IDRIVE setting. It should be evaluated at lower settings and when the device is powered off/on, reset to those lower settings every time. 

    Thanks,
    Aaron