LM3401: Unstable Conditions above 15V

Alain Fuchs

Prodigy 60 points

Part Number: LM3401

Dear TI Forum

I am having trouble with the LM3401 Board.

It is working fine when <= 14.5V is applied.

When Voltage is around 15V the LED is flickering and above 15.5V the LED is stable but Power is 50%.

Red Probe = LED Voltage

Yellow Probe = LM3401 L,D, P-MOS connection point

Stable running <= 14.5V stable 10W LED output

>= 15V unstable conditions and half power LED 5W output

LED Cree 3.2V@2.4A

Capacitor: C5750X7R1E226M250KA TDK

Coil: SRP1770TA-220M BOURNS

Diode: SSB44 VISHAY

Mosfet: IRF7416TRPBF INTERNATIONAL RECTIFIER, also tried STS6PF30L

Also tried C302 100nF instead 1uF for noice reduction

Also tried L301 15uH instead of 22uH

over 3 years ago

0 Sean Zhou over 3 years ago

TI__Mastermind 22745 points

Hi Alain,

What's the output LED counts? you have mentioned that the ">= 15V unstable conditions and half power LED 5W output", have you tried with different PWM duty cycle?

Sean

0 Alain Fuchs over 3 years ago in reply to Sean Zhou

Prodigy 60 points

Dear Sean,

I have one LED installed. PWM ist no issue, I run the tests under 100% PWM signal = full power.

Best regards,

Alain

0 Sean Zhou over 3 years ago in reply to Alain Fuchs

TI__Mastermind 22745 points

Hi Alain,

Please refer to "Figure 16. Switching Frequency and Ripple Current vs Hysteresis" to adjust the resistor connected to Pin 4(HYS).

Sean

0 Alain Fuchs over 3 years ago in reply to Sean Zhou

Prodigy 60 points

Dear Sean,

ok thanks a lot. Solved the problem.

Either highering ILIM Resistor or lowering HYS solved it.

Now I reduced HYS Resistor to 1.8k to have arround 0.18A ripple current.

Yellow = PMOS,D,L

Purple = Gate of Mosfet

Blue = LED Voltage

Green = Power Input

Best regards,

Alain

Power management

Power management forum

LM3401: Unstable Conditions above 15V