LM3409 malfunction

Ramiro Polo

Hello everybody,

I have designed a PCB board to drive 12 leds, 6 pus other 6 in parallel conection.

The requirements for this design are 24V input, and adjustable current from 0 to 1.6A via I_adjust analog pin.

The circuit dont work, the leds have the same voltage that Vinput. P_GATEworks, but with a signal independent of the voltage of the I_adjust pin.

When I turn Enable pin to 0V, the circuit blocks the current.

The circuit is the next:

And the LEDS are SMB760-1100-05-I model from USHIO. Datasheet attached:

6874.SMB760-1100-05-I.pdf

Regards,

Ramiro Polo

over 11 years ago

0 Prasad Dhond over 11 years ago

TI__Intellectual 855 points

Can you send a plot of your PGATE signal? Is it possible to test the output voltage by disconnecting IADJ from the Digital Pot?

0 Ramiro Polo over 11 years ago in reply to Prasad Dhond

Prodigy 60 points

Hi Prasad,

Thanks for your answer.

Now I have the circuit controlled by a manual multiturn pot, and with a resistive load of 100 Ohms.

The output current is always 0.23 A in the next situations:

V (I _adjustpin) = 0.23V:

V (I _adjustpin) = 0.4V:

V (I _adjustpin) = 1 V:

V (I _adjustpin) = Disconnected

And the next case is Iout = 0 A when Enable is tied to 0V.

Regards

0 Prasad Dhond over 11 years ago in reply to Ramiro Polo

TI__Intellectual 855 points

Have you tried the circuit with an actual LED load instead of the resistor?

0 Ramiro Polo over 11 years ago in reply to Prasad Dhond

Prodigy 60 points

Yes. I used the LEDs.
The current limit was increased to achieve 24V at the laboratory power supply and then the LEDs were burned out.
But the effect in the circuit was the same as with the resistor, until LEDs were burnt .

Regards

0 Ramiro Polo over 11 years ago in reply to Prasad Dhond

Prodigy 60 points

Hello,

I have revised the circuit, I have simulated it in Webench and TINA, and I think that the schematic circuit is correct. Is that true? Do you think that this circuit is correct for the USHIO leds?

I send you PCB board design to verify that is correct or not.

2335.PE-FLUOR-F-V1.pdf

Regards,

0 Ramiro Polo over 11 years ago in reply to Ramiro Polo

Prodigy 60 points

Hello everybody,

The circuit works correctly.

There was a component fitted in a bad position. Now the circuit works fine.

Regards

Power management

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LM3409 malfunction