TPS92602-Q1: PWM dimming light LED very slow

Hi Janson,

Does the long delay only happen when the load is very light? What if you apply higher voltage on ICTRL pin or use a higher PWM duty cycle?

Best regards,
Shirley He

Hi Shirley :

Yes, this problem happen when load is light. Increase PWM duty cycle and decrease compensation capacitor C20 value can improve it. If PWM duty cycle does'nt change and decrease C20 to 0.022uF then the light up time is acceptable but could I change C20 value?

Best regards

Janson

Hi Janson,


Very low ICTRL voltage and low PWM duty cycle will cause the current-sense error amplifier output voltage (COMP voltage) increase very slowly. May I ask why so light load is needed? 0.06V on ICTRL pin means output current is only 4% of full range current. And 1% duty cycle also leads to very low brightness. What is the maximum output current requirement of your design? If it works at light load at most of the time, then you can increase the output current sense resistor RLED_SNS and increase ICTRL voltage. It can help to reduce the startup time.

Best regards,
Shirley He

Hi Shirley :

My product spec of dimming range is 0.1mA to 750mA. Only low ICTRL voltage + PWM dimming can achive 0.1mA cuurent so I can't increase ICTRL voltage. Rsense is 0.2 ohm because maximum current is 750mA. It seems these two items can't modify because my dimming range. Does any other method to improve startup time?

Best regards
Janson

Hi Janson,

In that case, reduce the compensation capacitor can reduce the startup time, as you did. You just have to ensure loop stability and good dynamic response at all working conditions.

Best regards,
Shirley He

Hi Shirley :

Does this compensation capacitor have minimum and maximum value?

Best regards
Janson