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LM5069: LM5069-1 Operation Related Inquiry

Grady Lee
Genius 4215 points
Part Number: LM5069

Tool/software:

Hi, TI expert

The customer has a question about the circuit operation by applying LM5069-1.

The product uses a DC motor to drive the recliner sofa and is connected to a full bridge circuit.

The circuit design was made to protect the circuit in case of a short circuit in the motor.

- The product uses a 29V, 5.25A, DC adapter.

- The DC motor is driven in the recliner sofa and used for posture control (control is done using a Micom).

- The schematic is as follows.

(Question)

Q1) When the circuit is configured and a faulty motor (short) is connected and operated, the protection circuit operates as shown in the waveform below, but I don't understand why the waveform below appears.

(Blue: DC_IN voltage, yellow FET gate voltage, green 29V voltage, purple current flowing through the FET)

The short circuit current flowed and the FET was cut off, but the voltage rose to about 10V again, and the current flowed for about 4msec and then turned off.

Q2) At first, when applying 1ea FET (DMN4010) to the circuit below and testing, the load was normal, the FET short-circuited in the faulty motor.

(Gate, drain, source all 0 ohm) So, when 2 FETs were connected in parallel, it worked normally. (Protection circuit worked normally)

I think the capacity of the FET is sufficient, but can you tell me why this phenomenon occurs?

(FET is DMN4010_Diodes)

DMN4010 (Diodes).pdf

Q3) Can you recommend another suitable FET for this? or is there another better solution?

Please check. Thank you.

  • 0
    TI__Mastermind 39820 points

    Please see the below screenshots captured from the datasheet. 

  • 0 in reply to Avishek Pal
    Genius 4215 points

    Hi, Avishek Pal

    The customer has additional questions.

    1) Is it right to consider the phenomenon inquired about above as a normal phenomenon in the schematic above?

    2) If I change the C43 value of the timer pin from 104 (100nF) → 103 (10nF), will the time be shortened? Will there be any other problems if I change it like this?

    3) If I change the resistance value of the PWR pin from 27Kohm → 100Kohm, will the current decrease after the breaker is triggered? Will there be other problems if I change it like this?

    4) The sensing resistance is 5mΩ, and the calculated value that the breaker can occur below is 42A, and the maximum current of the current FET is 39A, so I understand that the FET will be damaged if the breaker occurs when used alone. Is that correct?
    In this case, how many A of FET can be used without problems?

    Please check. Thank you.

  • +1 in reply to Grady Lee
    TI__Mastermind 39820 points

    Please fill out the design calculator.

    www.ti.com/.../LM5069QUICK-CALC