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DRV8705-Q1: about LDO & motor driver power supply discussion

zhengwei zhou
Prodigy 95 points
Part Number: DRV8705-Q1
Other Parts Discussed in Thread: DRV8705H-Q1EVM

According to the SCH above,LDO  power input is from Node 2，after PI filter.

This design is from DRV8705H-Q1EVM,the link is as below:

 www.ti.com.cn/.../DRV8705H-Q1EVM

Why not LDO power input connected to Node 1?

Is there  EMC test data to support this design?

I think Node 2 is more noisy than Node 1 while the motor is running.

  • 0
    TI__Mastermind 37683 points

    Hi Zhengwei,

    zhengwei zhou said:
    Why not LDO power input connected to Node 1?

    The reason is because we need the PVDD supply to come AFTER the Pi filter to filter out any differential noise coming from the main power supply line.

    zhengwei zhou said:
    Is there  EMC test data to support this design?

    It seems we don't have this data available at the moment.

    zhengwei zhou said:
    I think Node 2 is more noisy than Node 1 while the motor is running.

    This would be true if the current flows back to the power supply which can happen when the decay mode is set to diode frewheel (COAST) mode.