TPS61236P: Converter circuit produces audible noise and big ripple

Hi 

could you share the schematic and the input voltage waveform? it seem like the device is unstable or trigger current limit

Hi Jasper Li,

The layout was posted in the original question and schmetic is attached below, the waveform of Vin will be uploaded later.

Thanks a lot.

Hi

did you try to reduce the R3 to zero? not sure if current limit is triggered.

Hi Jasper Li,

It's very weird that during the test carried out just now, no so big ripple was checked out. It seems that the state of big ripple is unstable, only when the current is around 4A can the unstable state continue a short period of time. And also, it seems that CC didn't work very well, since I found it's easier to control the current to 4.25~4.29A. When the resistance of the load become more smaller, the over current protection will likely shutdown the converter. The waveforms are shown below, the channel 0 is Vout and the channel 1 is Vin. p.s.: The current shown in the waveforms are the output current.

Thanks a lot.

Hi 

it seem the device is unstable caused by the voltage loop or the CC loop or both

1. please try to reduce the R3 to 0 and check the waveform (not the solution, but try to understand the root cause)

2. if we can still see the behavior at R3 = 0, please remove the C2. 

Hi Jasper Li,

I've done the test and the result shows that no matter whether it's working in CC or CV mode, there is no obvious difference in output behavior. In fact, the tested constant current is not exactly 4A but approximately 4.12A, which may caused by the CC inaccuracy (+-10% according to the datasheet). But the large ripple state is still unstable, no matter whether CC is enabled or not (see picture 1 & 2), the state only occurs when the output current is slightly lower than 4A. Futhermore, a more weird phenomenon was detected (see picture 3~5). This mainly occurs when the temperature of IC is relatively high, maybe also when the ESR of Li-ion power suppply is relatively high in the meanwhile. When this occurs, the input current is nearly same as the output current but there is a voltage drop close to 3V divided into the converter. Seems that the themal shutdown trys to work but turns to a failure and the high side MOSFET is not completely shutdown.

Thanks a lot.

Hi 

the device will try to recover after thermal shutdown. during the recovery, the high FET will be turn on to change the output capacitor.  if the loading is very large during the period, the high FET is always on, but the output voltage doesn't reach setting value. 

you could also try to increase the COUT to stabilize the IC.

Hi Jasper Li,

So is there any need to remove C2?

Thanks a lot.

Hi 

you could also try this to check if it is help.

Hi Jasper Li,

Since this converter is designed for a type of laser diode which requires constant current, I couldn't test whether the converter will still produce big ripple or not when the load is applied unless I get one. Applying a resistor as load is meaningless, due to their voltage-ampere characteristics are not consistent. Please give me more time.

Thanks a lot.

Hi 

thanks, wait for your update

Hi Jasper Li,

I've done the test. The big ripple still exists when the load is applying, even only for a little while. I have tried to connect a 1000uF-aluminium polymer capacitor in parallel with the output, but in vain. The ripple still exists. Now I'm trying to change the Rcc to reduce the CC to 2A, then connect two converters in parallel to build a 4A converter. May be this will work.

Thanks a lot.

Hi 

thanks, wait for your update.

I would also suggest you apply an EVM for reference.