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DRV8434S: Caps on AOUT and BOUT

Darren Jenkins
Genius 12461 points
Part Number: DRV8434S

Motor Driver team,

The EVM for DRV8434S has 3.3nF caps on each output AOUT1, AOUT2, BOUT1, BOUT2.  These are listed as DNP.  Can you explain when you would recommend installing them and why they are DNP?

Our customer is considering adding 100nF caps there and would like to understand the decision on the EVM board design.

Thanks,
Darren

  • 0
    TI__Mastermind 44325 points

    Hello Darren,

    The 3.3 nF caps help with ESD mitigation. Such small capacitors are commonly used in stepper drivers output terminals. We have made these optional (DNP) in the EVM to allow the user to evaluate the driver with no additional capacitive load on the outputs. Capacitive load will result with increased switching losses due to capacitive conduction of the chopping frequency and additional heat in the driver. We do not recommend using 100 nF caps as these would significantly increase switching losses and overheat the driver and may lead to a TSD situation, especially at higher VM supply voltages. Based on the drive requirements, it is up to the customer engineer to make a trade off between maximum power dissipation and load capacitor values. 

    What is the motivation to consider 100 nF? I have seen some customers use up to 10 nF for EMI mitigation at the expense of higher operating temperature of the device. 3.3 nF or lower is the commonly use value for these caps.

    Regards, Murugavel