LM3409HV: LM3409HV IADJ dimming

Eric Shen42

Part Number: LM3409HV
Other Parts Discussed in Thread: LM3409

Dear TI:

My customer used LM3409HV for LED driver, they used IADJ for dimming, but they found when PIN IADJ connected GND, the output current still has 7mA, the PIN PGATE also has the output to driver MOS, customer hope when IADJ=0V, there is no output current.

I found the graph of datasheet Figure 12, when IADJ=0V, the ILED is not 0A, so does used IADJ dimming the current can't be 0A?

Please help to check the problem, thanks!

Regards!

Eric Shen

over 6 years ago

0 Irwin Nederbragt over 6 years ago

TI__Mastermind 28655 points

Hello Eric,

The LM3409 is a constant off-time controller. After the off-time there is a minimum on-time that is 115 ns typical, 211 ns max. This means there will always be some current flowing to the LEDs. Things to reduce this are increasing the inductance value and lowering the switching frequency. You can also provide a load to the output to burn that extra current. To go to zero current you can either pull EN to gnd (low power mode) or pull UVLO below it's threshold.

Best Regards,

0 Eric Shen42 over 6 years ago in reply to Irwin Nederbragt

Expert 2750 points

Hi Irwin:
Thanks!

Regards!
Eric

Power management

Power management forum

LM3409HV: LM3409HV IADJ dimming