• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 3 answers
  • Subscribers 64 subscribers
  • Views 2243 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM5069: Surge Protection

Brian Wang0928
Genius 13020 points
Part Number: LM5069

Application: motor driver with high power

Customer wanna to know the principle and function of the D2 and R6 on LM5069EVM. Why both D2 and D6 are not required when the resistive path between Vin and GND pin of the LM5069 is less than 1M Ohm? What situation does the circuit of the D2 +R6 path be activated?

Please check if below circuit is ok or not? Very thanks. 

 

  • 0
    TI__Guru** 104991 points
    Hi Brian,

    When the input voltage quickly transition from positive to negative, the device turn OFF speed gets affected if the Vin to Gnd resistance is high. The D2 + R6 gives a path to VIN to discharge the GATE pin in the case that there is residual charge on the MOSFET gate after VIN goes negative.

    Best Regards,
    Rakesh
  • 0 in reply to Rakesh
    TI__Genius 13020 points

    1. What are you talking about is that the Input voltage is in turning-OFF transition state, right? Does this D2+R6 configuration to speed up the turning-off speed?

    2. Is 1M-Ohm R6 good enough to discharge the GATE pin?Is it better as lower as 1M-Ohm?

  • 0 in reply to Brian Wang0928
    TI__Guru** 104991 points
    1A> Yes. When Vin goes towards -ve during transient, the device won't have input source to keep the GATE in active pull down mode, leaving the GATE node floating . D2+R6 provides the path for GATE to discharge any residual charge and make sure it is not left floating

    2A> 1M-Ohm is good enough as it is just to ensure it is not left OPEN.

    Best Regards,
    Rakesh
  • 0 in reply to Rakesh
    TI__Genius 13020 points

    Thanks. One more questions.

    1. Do you prefer removing D2+R6 when Resistor between VIN and GND is less than 1M Ohm? In the appication guide, it's using both D2+R6 and resistor <1M Ohm.

    2. When using Resistive <1M Ohm between VIN and GND, how to discharge the residual chare of the MOSFETs? WHat's the discharge path?

    Regards,

    Brian

  • 0 in reply to Brian Wang0928
    TI__Guru** 104991 points
    1A) Yes, D2+R6 can be removed when Resistor between VIN and GND is less than 1M Ohm
    2A) During fast negative transient, the high dvdt causes the current to flow through the FET parasitic cap (gate to source, gate to drain). These capacitances will find discharge path from VIN to GnD, so, lower than 1M helps to drain these charge.
    Since, it is dependent on slew-rate of VIN and FET parasitics - I would still recommend to put placeholder and then decide during testing.

    Best Regards,
    Rakesh