TPS563200: Audible high pitch squealing from the circuit

Hi Robin!

The first thing you need to confirm is that whether your SW waveform is stable. 

Generally, the audio noise happens on light load, it is because that the switching frequency maybe lower than 20kHz during light load.

If the noise still exists with full loading, such as 3A, it is usually caused by stability issue. You need to provide specific parameters of you SCH and layout for double check.

Shuai

Hello Shuai!

Thanks for your message.

How can I send you the images, it won't let me upload them, asks for a URL!

The operational load is from 180 to 300 mA normally, if peripherals are connected in can increase to 2 amps.

The SW waveform goes from a square wave with 2.5uS period, and then collapses to 0v, with very high frequency reducing voltage, like a ringing.

The output voltage is quite stable, it has the typical saw tooth waveform on the ripple as shown in the datasheet, but over 100mV.

Our PCB has no ground plane under the inductor as detailed in the example provided by TI.

I would send you photos if you can tell me how.

Regards, Rob

I think may I have found the problem in the VFB line.

The resistors that set the VFB voltage for 5V from the datasheet are 54K9 and 10K, and it says in the datasheet:-

"To improve efficiency at light loads consider using larger value resistors, too high of resistance is more susceptible to noise and voltage errors from the VFB input current are more noticeable."

If I touch my scope probe onto the VFB pin, or between the two resistors, the pulsing noise virtually disappears, so I added 100nF to ground, and it had the same effect.

The approx. 300mV saw tooth ripple on the 5V output is much more stable, but in the datasheet it's shown as 20mV.

The SW line is a 12v square wave with 2uS period, its running square waves for 100 to 400uS then drops to 6v, half, for about 40uS.

Our board has an audio amplifier, so the current requirement surges with the music, and if I keep the volume low, the TI regulator is much more stable.

I put a 220uF 50V capacitor on the 563200 output, that changed the frequency of the regulator but the interference persisted.

Current draw surges from 0.3 to 1.0 amps to power the amp for the audio speaker.

I hope that's enough information for an engineer familiar with the 563200 to have a good idea what the problem is.

So the VFB feedback resistors are thick film 62mw 0402 smt, as there was a 3mm track between them, I wondered if that was enough to pick-up EMI.

So I moved the 12V side resistor right together with the ground side resistor, and bam, interference virtually eliminate!

"Figure 8-13 Typical Layout" didn't stress the critical nature of the resistor layout, so perhaps there is an issue which is causing this hyper sensitivity.

Reducing the track length from 3 to 0 mm between the feedback resistors has made an immense improvement, the ripple has reduced 600% to 50mV.

The track distance from the VFB pin to the resistor dividers is 2mm, and the PCB CAD tools don't allow closer placement, so what is the cause of this instability in the TPS563200?

Hi, here is the board layout

I pasted the photo, an image black showed and then deleted itself so doesn't seem to work.

Are you a TI engineer, and familiar with this IC?  You should be able to give me some guidance with the info I supplied in text.

I an using the latest MS Edge browser, which is based on Chrome.  This page will not allow small jpg images to be pasted.

Hi Robin,

Please send the waveforms to me via my email, I will feedback to later. harry.zhou@ti.com 

Best regards,

Zhou

I sent them to your email a few hours ago.

Hi Shai, this is quite urgent, our production is held up for this problem, can you get back to me as soon as possible please?

When the audio amp get a large input signal, drawing more current, it looks like the SW pulse collapses for approx. 20 to 200 uS.  The SW pulse from the scope images I emailed you is around 650 KHz as per the datasheet.

The 5V output remains reasonably stable, but there are bursts along the 100-150mV noise that seem to match up to the audio.

The NS4160 Nsiway audio IC draws as much as 1.2 amps with 2 watts out, I added a 100uF capacitor across the audio IC power pins, right on top of the SOP8 IC, but it made no difference.

If I run with the audio right down, the audio is noise free, but there are still some collapses in the SW signal as shown on the scope image.

Total maximum current draw is under 1.5 amps.

I'm currently at a loss as to what to try next!

Damn, I just found this thread from 8 years ago with the exact same problem, eco burst mode issue, they swapped out the 320 for a 54202 to solve the problem, saying that the 320 is basically a weak design!!

TPS563200 failure mode operation. - Power management forum - Power management - TI E2E support forums

Is this a known problem?  Should I try the TPS54202DDCR?

I have to say I feel like I'm talking to myself here :/

The TPS563200DDCR is working well after adjusting the feedback voltage layout, but there seems to be an unusual situation when the external 12V supply is disconnected and the USB cable is connected.

This puts the USB 5V into the board to power it, and puts 5V onto the SW pin of the 563200, and it looks like the TPS563200DDCR is feeding current to it's VIN pin, powering some of our 12 V rail, with 4.3 V and at least 60 mA.  Checking with a multimeter, the resistance from SW to VIN is just 500 ohms with the chip powered off.

Would you know if this is a known characteristic, and if it can damage the chip?