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DRV8873-Q1: Capacitor Requirements for DVDD and VM

Shinichi Yokota
Genius 9715 points
Part Number: DRV8873-Q1

Hello,

The DRV8873S-Q1 data sheet specifies capacitance and voltage rating values for external decoupling capacitors of the DVDD and VM pins, but is it OK to change the capacitance value? If yes, what are the acceptable ranges?

Perhaps, there could be a chance to optimize schematic so that the system can satisfy EMC requirements. I'd like to know in advance what could be possible for the DRV8873S-Q1.

Best regards,
Shinichi Yokota

  • 0
    TI__Guru** 114905 points

    Hi Yokota-san,

    The design has been simulated and verified with the recommended 1uF DVDD capacitor and a 100nF capacitor placed near the VM pin. In addition, a bulk VM capacitor is needed.

    There is some allowed variation of the capacitors. Typically the device can accept +/-50% variation.

    Changing the slew rate should help reduce EMC issues. Adding a PI filter on the VM input can also help.

  • 0 in reply to Rick Duncan
    TI__Genius 9715 points

    Rick-san,

    Rick Duncan said:

    The design has been simulated and verified with the recommended 1uF DVDD capacitor and a 100nF capacitor placed near the VM pin. In addition, a bulk VM capacitor is needed.

    If the external capacitor has a role of phase compensation for the internal LDO's negative feedback, for example, capacitors with the specified capacitance values must be put on the DVDD and VM pins. Otherwise, the capacitance values can be chosen/adjusted based on the circuit's test results, I guess.

    Do we need to keep the specified values for these external capacitors? What ranges are acceptable for these capacitance values?

    Best regards,
    Shinichi Yokota

  • 0 in reply to Shinichi Yokota
    TI__Guru** 114905 points

    Hi Yokota-san,

    It is recommended to keep the specified values.

    The DVDD capacitor does have a role of phase compensation. That is why the DVDD capacitor is recommended in the datasheet.

    The design team recognizes that there is some variation in ceramic capacitors due to tolerance and DC bias. That is why the team also checks for ~50% variation.

    The 0.1uF ceramic capacitor on VM helps prevent droops in the VM voltage when the output has capacitors. This capacitor should have similar frequency response and ESR characteristics.

  • 0 in reply to Rick Duncan
    TI__Genius 9715 points

    Rick-san,

    I understand about the DVDD pin.

    If the capacitors on the VM pin don't have a role of phase compensation for stability of internal negative feedback circuits, for example, I guess the capacitance values can be adjusted from the recommended values as PCB supply patterns may differ from what TI assumes. I suspect the recommended values on the VM pin were decided so that a voltage transient change on the VM pin will be within a certain range.

    My question asks if the recommended values are "MUST-keep" ones or "CAN-keep" ones. In other words, how much room the capacitance values on the VM pin can be changed?

    Best regards,
    Shinichi Yokota