TPS92513HV：TPS92513HV noise issue

Hi Terence,

Are you talking about the noise at ISENSE pin? The 150mV peak-to-peak at ISENSE pin is not noise because the current sense feedback directly represents the inductor current. That being said when PDIM is high, TPS92513HV is switching and inductor current ripple shows up at ISENSE pin. If you increase PDIM frequency to 100kHz, the loop bandwidth may not be that high and won't output the right PWM dimming.

Hi Yichao:
The noise is by the TPS92543HV in the operation. especially when the PDIM frequency is smaller than 1Khz.
I can determine the noise that comes from the inductor.
Actually, when the PDIM is over than 100Khz, the output current waveform is not correct.
It became like a continued sin waveform, not like the square

 雜音是TPS92543HV 在工作時才會產生.特別是當 PDIM 頻率小於 1Khz 時。
我確定雜音是從電感來的。
事實上，當PDIM超過100Khz時，輸出電流波形的確是不正確的,它變得像連續的正弦波形而不是方波

Hi Terence,

To clarify the noise, can you provide the operation waveform where you determine the noise? When PDIM is high, the ISENSE pin is supposed to see triangular ripple waveform that is proportional to inductor current. I would not say that is noise. When PDIM>100kHz, the output current square waveform is filtered by inductor and output capacitor due to the low output bandwidth. One can try smaller inductance and output capacitance to improve it.

Hi Yichao:
The noise is meant audible.it is like the buzzy shaking sounds.
The figure test conditions:
Vin：48V
Vout:10V
PDIM: PWM F=1Kz duty 50%
Iout:1.5A
RT=110K F=1MHz
Ch1：PDIM signal (F=KHz duty 50%)
CH2：Isense voltage waveform
CH3 : Iou current waveform

Hi Terrence,

Thanks for the detailed info. The CH2 Isense voltage seems reasonable as it represents the inductor current. Can you show zoom in waveform of CH2 at switching frequency scale? What inductor have you selected, since the audible noise comes from it? Make sure it is not saturated.

Hi Yichao :
1.I zoom the CH2(Isense) and measure the frequency.
but the frequency does not cycle. so I use the cursors to measure.

2. In the inductor used. I have tried two inductor values whose package is not the same.
but the audible noise is still can be eared.

Hi Terrence,

The Isense waveform seems normal. Since the audible noise comes from the inductor, the operation PDIM frequency range is better to be >16kHz to avoid that. However, the output current dimming ratio might have mismatch to ideal if the PDIM frequency is much higher than 1kHz. That's why the spec defines the PDIM range up to 1kHz. The output PWM current may be totally distorted by output filter if frequency is close to 100kHz.

One suggestion is to try PDIM frequency >20kHz and see if audible noise is acceptable. Meanwhile, you can reduce the inductance to increase the output bandwidth and reduce the PWM dimming mismatch and distortion.

Also, we have a new device TPS922052 which can run >20kHz PWM dimming with improved dimming performance. It also supports analog dimming and hybrid dimming that can reduce the current magnitude when running PWM dimming. It can dramatically reduce the audible noise and output distortion due to the low magnitude of PWM current.

If you are interested in this new device, pls let me know and we can share its detailed info.

Hi Yichao:
The audible noise will be deleted which adjusts the PDIM >16Khz and decrease the inductor.

If LED must be operated in the linear for the adjustment.
So the PDIM must operate <1Khz.

Is the audible noise in the circuits will cause any side effects?
(ex... EMI or inductor broke due to high-frequency shaking?)