TPS61042: LED does not light up at 1% duty ratio

Hi Keng,

    How about the PWM signal quality? Have you try other devices or try with signal generator?

BR

Sean

hi Sean,

Please advice.

Best Regards,

kpk

Hi kpk,

     Coudl you provide the waveform of "SW", "Vout" and "Iout" when you decrease the PWM duty cycle to 1%? I want to check whether this device is working or not?

BR

Sean

hi Sean,

Kindly refer to attach and advise.

3056.Doc1.pdf

Hi keng,

    Thanks for the test waveforms, and it is really strange that your output current is PWM waveform, it should be constant since TPS61042 works under analog dimming mode, and can you mar sure your output voltage is larger than the Vin? you cna also try to increase the R48 value to about 20ohm and test again?

BR

Sean

Hi Sean,

Another question, Is it impossible to flow current to LCD from LED driver which 20KHz and duty 1%?? 

best regards,

KPK

Hi KPK,

     For TPS61042, it can achieve 1% with 20kHz dimming frequency. Our dimming frequency varies from 100Hz to 50kHz. And for this whole dimming frequency, it can both achieve 1% to 100% dimming. It is really strange for your question, how about your output voltage? You have shown two LEDs serially. I want to know the forward voltage range of the LED string. Maybe you can request one TPS61042EVM to evaluate with our EVM.

BR

Sean

i Sean,

We found that out put voltage did not satisfy Vf of LED when input PWM signal is 20KHz and duty 1%.

Please advise how to increase output voltage.

best regards,

kpk

Hi kpk,

    The current waveform is strange and wrong since our LED driver should deliver continuous current instead of the PWM waveform as shown in your waveform. have you ever try with another chip or change to another dimming frequency?

BR

Sean