TPS65131 Converter +15V Supply Rail Shutdown

Hi Brigitte,

Thanks for your reply.

Here is the Schematic diagram i have used.

In Schematic diagram i have mentioned Input inductance as 22uH, later i have changed to 6.8uH. Remaining things are same as schematics.

Here is the answers to your questions,

1) - Does the IC behave differently with PSP enabled or disabled?

YES. When i enable the PSP pin, the ripple magnitude at the output of converter (@ 15V terminal) is 360mV, and converter operated in burst mode. Which is not acceptable in my application. So, i have disabled PSP. After disabling PSP (Connected this pin to GND), the ripple magnitude is less than 15mV.

But Negative supply (-15V ) doesn't have any ripple / oscillation problem, even though PSN is enabled. So, for present circuit PSN is enabled.

Actual load at output of +15V and -15V converter about 50mA (Approx.)

2) What happens when you remove the 47uF capacitor from the positive output?

In beganning i used 2 x 47uF at input. later i have replace one 47uF with 4.7uF (CER). So input has both 4.7uF (CER) and 47uF (TANT).

What does happen if remove 47uF ?

3) - What happens when you double CP capacitor?

I have never tried this. What happens if i increase the value?

4) When you have the feedforward structure on the top resistor is there a change when you remove it?

I tried with with different values like 20k, 33k, and 56k in the place of 100k. No significant performance improvement observed.

5) - Do you have an EVM and is it possible that you solder a unit that does not start onto this?

I dont have EVM.

Here is the waveforms i have captured when +15V fails.

Figure1: +15V Fail Condition1 during power ON - 4.3V at converter output

Figure2:  +15V Fail Condition2 during power ON - 4.3V at converter output

Sometimes converter works without any problem. Waveform @15V output at the time of power is as follows, At that time also peak voltage reaches to nearly 16V. But at all cases -15V section working without any problem.

Thanks for your good support

During first Power ON both +15V and -15V works fine and it works well continuously. But After few minutes, if i switch OFF the input supply and Switch it ON again, +15V fails. And +4.3V appears at output. But -15V supply is working without any issue all the time.

I need to wait for sometime or do ON and OFF (Toggle) of input supply, at some point of time +15V will come at output. And it will be available for long time. And if i switch OFF and ON imput supply (+5V), issues starts.

What shall be the rout cause for this ???

Hello Anand,

This is not normal behavior. To identify the root cause we need the tests that I asked for in my first post.

E.g. I need to know if the same issue happens when PSP is disabled or the big output cap removed. This might be a problem for your application at the end, but we need to understand first what causes the problem to find the root cause and solve it.

All the tests that I mentioned in my post shall help to find the root cause and solve it as fast as possible.

Do you have more than one board and do you observe this behavior on all boards?

Best regards,
Brigitte