TPS61194-Q1: light load lead the inductor noisy

Hi Roy,

• Can you provide the current of inductor when it generated the noise?
• Does inductor generated noise when the PWM is high at light load?
• What's the duty cycle of PMW input when the inductor generates the noise?
• Have you tried to change the PWM input frequency?
• Please provide more information when the inductor generates the noise.

Hi Charles,

Please see the comments.

Current of inductor when it generated the noise? The current consumption at light load is around 8~10 mA

Does inductor generated noise when the PWM is high at light load? The application is Vin/Vout = 16V/20V (The application of input voltage is 9~16V, and the Vout(LED) is about 20V at light load. Noisy occurred while high input voltage during light load)

What's the duty cycle of PWM input when the inductor generates the noise?  The minimum duty they applied is about 2% and it suffered the noise. But they didn’t check how lower the duty of PWM that starts to generate noise at their application.

Have you tried to change the PWM input frequency? No. To avoid audible noise, we always set WLED PWM frequency to 20kHz (or nearby 20kHz, like 18kHz). TPS61194 can’t apply PWM frequency higher than 20kHz. And we don’t lower the PWM frequency because it will lead to audible noise even at normal operation.

Hi Roy,

Please see the comments.

Current of inductor when it generated the noise? The current consumption at light load is around 8~10 mA

Actually I need the waveform of inductor current to identify the root cause for noise. The unstable of loop under light load will also lead to this phenomenon. And you will find low frequency component of inductor current.

Besides, is it possible to increase the value of inductor?

Does inductor generated noise when the PWM is high at light load? The application is Vin/Vout = 16V/20V (The application of input voltage is 9~16V, and the Vout(LED) is about 20V at light load. Noisy occurred while high input voltage during light load)

Will 100% PWM duty cycle input still generate the noise under this condition?

What's the duty cycle of PWM input when the inductor generates the noise?  The minimum duty they applied is about 2% and it suffered the noise. But they didn’t check how lower the duty of PWM that starts to generate noise at their application.

OK.

Have you tried to change the PWM input frequency? No. To avoid audible noise, we always set WLED PWM frequency to 20kHz (or nearby 20kHz, like 18kHz). TPS61194 can’t apply PWM frequency higher than 20kHz. And we don’t lower the PWM frequency because it will lead to audible noise even at normal operation.

Have you enable the spread spectrum when noise happens?

The waveform of inductor is important to figure the root cause.

Besides, I think it is better to communicate by emails for this case. You can email to me directly.

Hi Charles,

Sorry that I have another urgent case, I will send you e-mail directly afterward.

Roy

Hi Roy,

It's OK.