TPS92691 occur unstable operation by overcurrent on every PWM dimming start.
I guess that switching current increase more than overcurrent during PWM logic low state.
And continue to reach overcurrent on every PWM dimming:high.
Waveform for limit of stable (Iout is about 50mA), and unstable (more than 50mA) are attached below;
※Yellow: Vout, Green: PWM, Blue: Vsw, Purple: Isw
・Stable, but occur large switching current
・Unstable, inductor current rating was saturated
【Question】
I want to reduce switching current less than overcurrent, and I guess the most effect is reduce logic low time.
Please let me know about measure for suppress switching current.
※I try to change below parts, is there the other points?
・Increase Cout (Done) ⇒ Slightly improved
・Change to high current rating inductor ⇒ The present using 6A_max inductor, I think that should to change.
・Adjustment Ris ⇒ The present using 20mΩ
Additional question, is there the minimum value for Ris?
【Additional information】
・Low side current sensing, fsw: 200kHz, L: 33μH
・PWM frequency is 500Hz, results to changed 100Hz~1kHz were the same.
・The higher PWM duty cycle, the higher stable Iout range
・When adjustment soft start time, PWM tr/tf, and PWM amplitude, occur was not improve.
Best regards,
Satoshi
