ADP5056 - Not working in FPWM mode

Hi Selvaraj, 

Can you confirm exactly where you are measuring this from on your system? What issues it this causing the overall performance on the system?

Regard

 Ruairi, 

The attached waveform is measured at SW1 node of ADP5056. The output ripple of the power convertor is high (100mV in 1.3V rail, Allowed ripple is 5% (65mV). ADRV9002 chip in out custom board is not booting properly, we are getting the below error, "Time out waiting for ARM Boot to happen". 

Hi Selvaraj

I have moved this to the Power forum for better support on the APD5056 part. I will try measure the output from the part on my platform soon and see if I can re-create this but for now some insight from the power folk might help. 

Regards

Hi Selvaraj_K,

Can you try to isolate the ADP5056 first and double check if all the channels are producing the correct output voltage/current?

Hi Team, 

All three channels of ADP5056 is giving proper voltages. 

Hi Selvaraj,

Have you managed to debug this any further?

Hi Team, 

The issue has been resolved. Due to insufficient input capacitor this happened. We have added 47uF capacitor near ADP5056 input pins, it is working properly now. 

That's interesting to hear. Thanks for the update, and glad you got to the bottom of it.

We've had a similar problem with 3off of a new PCB we put together using the ADP5056 in FPWM mode, which had +1v8, +3v3 and +1v15 on channels 1-3 respectively, and our +1v8 CH1 waveform was similar to what you have posted - a couple of very high duty cycle pulses, then a lower duty cycle pulse, then skipping several pulses. The voltage ripple on this rail was terrible, and the very high duty cycle pulses hammered the +12v input rail from the bench supply during test. CH2 and CH3 worked exactly as expected, however.

After much revisiting of the design calcs, and component choices, I couldn't identify any problems. The PCB layout was completely symmetrical between CH1 and CH2 on our PCB, so it didn't seem to be a layout issue.

Components were almost identical in our design for CH1 and CH2 voltage and current choices, including input and output caps. So we swapped the feedback resistors over between CH1 and CH2, to put our 3v3 on CH1 and 1v8 on CH2 - kind of a last resort sanity check.  Having done this, the performance of both CH1 and CH2 were as they should have been from the start.

It's a head scratcher, for sure, but I will revisit our choices for input capacitance, in light of your update. Thanks!