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DRV8434S: Thermal shutdown of DRV8434SRGER

bonobono
Prodigy 50 points
Part Number: DRV8434S

Hello,
We are using a DRV8434SRGER under the following conditions, but it goes into thermal shutdown (OTSD).
The symptoms are the same for both the board we developed and the DRV8434SEVM board.
Could you please tell us the probable cause of this problem?

VM voltage: 24V
Vref voltage: 2.26V (@Vcc=3.3V)
Setting torque: 100%
Ambient temperature Ta: 25°C
Motor inductor: 6mH
Motor resistance: 1.7Ω

Best regards,
Naoki Takano

  • 0
    TI__Mastermind 19060 points

    Hi Naoki-san,

    If possible could you please provide answers to the following questions to get a better understanding of the issue:

    1. What is the step mode (Full-step, half-step, etc.)?

    2. What is your PWM switching frequency?

    3. How long is the motor running before thermal shutdown occurs?

    Best,

    David

  • 0 in reply to David Medis
    Prodigy 50 points

    Hi David-san,

    Thank you for your reply.
    I will answer below.
    1. -> 1/16 step
    2. -> 3200pps
    3. -> several minutes

    I will correct some of the information I provided.
    On the DRV8434SEVM board, the thermal shutdown occurs at Vref=3.29V.
    On the board we developed, the thermal shutdown occurs at Vref = 2.26V.
    We are currently investigating the cause of this problem, which may be due to differences in parameter settings or the heat dissipation characteristics of the board.

    The following are the results of evaluating two motors on the DRV8434SEVM board.
    1. Motor A (6mH, 1.7Ω), at Vref=3.29V (OTSD), Chip surface temperature over 120℃, Supply current 0.66A
    2. Motor A (6mH, 1.7Ω), at Vref=2.26V, Chip surface temperature 75.5℃, Supply current 0.35A
    3. Motor B (11.3mH, 3.5Ω) at Vref=3.29V (OTSD), Chip surface temperature over 120℃, Supply current 1.4A
    4. Motor B (11.3mH, 3.5Ω) at Vref=2.26V, Chip surface temperature 74.5℃, Supply current 0.65A

    Best regards,
    Naoki Takano

  • 0 in reply to bonobono
    TI__Mastermind 19060 points

    Hi Naoki-san,

    When setting the Vref=3.29V at 100% torque, the full-scale current is roughly 2.5A. The 2.5A specification is the maximum capability of the driver and will run into thermal performance if run at this setting. The IRMS current is the recommended full-scale current setting of 1.8A, which is close to what you see when you set the Vref=2.26V.

    The full-scale current is dependent upon the following characteristics:

    Suggestions for this issue would be to either run the full-scale current at lower TRQ_DAC% or reduce the Vref. 

    Thermal dissipation could also be assisted through exterior heat sinks that would assist in temperature regulation. 

    An additional suggestion would be to see how the thermals change at higher step rates.

    Best,

    David

  • 0 in reply to David Medis
    Prodigy 50 points

    Hi David-san,

    Thank you for your reply.
    Our board is made with a 2-layer board,
    The DRV8434SEVM board was a 4-layer board with almost solid GND on the inner layers.
    We found a big difference in heat dissipation characteristics.

    This time, we set Vref to 3.3V for evaluation, but we plan to lower Vref for actual specifications.

    We will consider changing the number of layers on the board and the IC package.

    Thank you very much for your response.

    Best regards,
    Naoki