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LM3406HVEVAL: LM3406HV

giovanni copler
Prodigy 185 points
Part Number: LM3406HVEVAL
Other Parts Discussed in Thread: LM3406, LM3409

HI,

I'm try to evaluate the LM3406HVEVAL board with 2 wire pwm input power supply.

I set the output current to 350mA, i connect my cob led (VF=36V).

With dc 48V the board function well

Then i connect the 2 power supply wire to the output of a pwm dimmer. the output of this dimmer in an open drain type.

When power on, the output start from 0% until 100% of pwm.

But after power on, the lm3406 burn !!!! the polary it's ok, for 2 time this happened, and i can't understand why

  • 0
    TI__Genius 14940 points

    No，LM3406 delivers constant inductive current and you need to provide the current path always. 

    Please refer to 8.15 open circuit protection. You may use Dim

     pin for PWM control, or you can use Shunt current control like LM3409 etc.

  • +1 in reply to Xiaoguang1
    Prodigy 185 points

    ok, LM3406 have a DIM pin for pwm, but also can use a pwm method on power supply line, as indicated on datasheet. This method use a diode in series to Vin pin and use Vins pin to sense voltage

    I provide pwm on power supply line, by connecting and disconecting the negative pole of the power supply unit from gnd  input of EVAL (this throught the mosfet, as in my previous schematic, this is the normal schematic of a dimming unit for led

  • 0 in reply to giovanni copler
    TI__Genius 14940 points

    When using PWM method on power supply line, it means that you can shut down power supply or disconnect VIN+, not disconnecting the power supply GND and EVAL gnd. Disconnecting the power supply GND and EVAL gnd creates open circuit condition. You may use this method to control linear control or voltage control mode devices, but not devices like LM3406 which controls inductor current. As load current is inductive, when gnd is broke, the energy stored in the inductor has to find way to be discharged, which causes high voltage at Vout PIN and might even damages the device. This is same with the case mentioned in the datasheet. Please refer to below for details. 

     

    It is recommended to use DIM pin, SUPPLY on/off or shunt dimming( refer to LM3409 datasheet or 8.6.4 REMOTE LED ARRAYS) solution to control LED dimming.