IRPS5401 hiccup on startup

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Jim_Brady
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Hello,

I am having a problem with an IRPS5401 on a new board design.  It is hiccupping on startup even though the load current is much less than the over-current fault limit, including capacitor charging current.

It hiccups a few times, then comes on and stays on, see the two scope photos.  The measured load current reaches about 0.2 amps when it hiccups, see scope photos.  The capacitor charging current C dv/dt is 125uF * 3.3V / 5msec ramp time = 0.0825 amps.  So the total current when it hiccups is about 0.28 amps.

This is on PMIC output D, and I have the programming file set to a 5msec on ramp time and an over-current fault limit of 1.3 amps.  So it should not hiccup at 0.28 amps, is that correct?

Please tell me why the IRPS5401 could hiccup at this low current?  I am attaching two scope photos of voltage and current, the current measurement circuit I am using, and the programming file (zipped).  

Thanks for the help,

Jim Brady

 

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Nishanth
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Hello @Jim_Brady ,

Thank you for the data and waveforms.

The recommended minimum inductance value is 1.6uH for 12V input and 1 to 1.5V output at 800Khz as shown below.Nishanth_0-1680590515049.png

Kindly increase the inductance value and verify.

Regards,

Nishanth

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Nishanth
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Hello @Jim_Brady ,

Thank you for contributing to the Infineon Community.

Are you getting any faults in the status window of the PowIRCenter GUI?

Regards,

Nishanth

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Nishanth ---

Yes, I am seeing over-current fault and warning.  I am attaching screen shots of (a) status window and (b) command window for switcher D, which is the one that is hiccuping on startup.  As mentioned it hiccups a few times, them comes on steady.

The hiccups occur at about 0.25 - 0.30 amps, including calculated capacitor on-ramp surge current, but the over-current fault limit is 1.3 amps.  My question is, why would the PMIC overcurrent fault at much lower than the limit setting?

Thanks,

Jim 

  

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Nishanth
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Hello @Jim_Brady ,

Thank you for the GUI screenshots.

We are trying to identify the issue.

Kindly check the following:

  1. Increase  IOUT_OC_FAULT_LIMIT to 2A and check if the same behavior is observed.
  2. Increase TON_RISE and check if the same behavior is observed.
  3. Is this hiccup occurring every time the part is powered on, or is it random?

Kindly provide the following data:

  1. Inductor current waveform of Switcher D
  2. Output voltage rise time captured at 5ms/div (to observe initial rise time)
  3. Waveform of the input voltage
  4. Waveform of the switch node
  5. Bode response (if available)

Regards,

Nishanth

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Nishanth ----

I have made the measurements you requested. But before mentioning, I would like to ask if you think the inductance I am using is too low, and could this by why the PMIC is tripping OC fault? Please see the PMIC schematic of my board, attached.  I am using 1.3uH (switcher D) which is lower than your demo board uses (3.3uH), and it seems like the inductor switching current may be too high. My load current on switcher D is about 100mA. 

1.  Attached is a scope photo showing the PMIC output voltage (switcher D) at power-on.  Scope horizontal speed is 4msec/division.  This is with the program file set to on ramp time of 5msec.   This is one of the few times it did not hiccup at power-on.

2. Attached is a scope photo showing the PMIC input voltage at power-on.  Scope horizontal speed is 1msec/div.  

3. With the PC fault limit at 1A, 5msec on-ramp, it hiccups almost every time at power-on.  Sometimes it hiccups only once or twice, but sometimes it hiccups like ten times.  And this happens on all 3 boards I have.

4. I increased OC fault limit from 1A to 2A, still 5msec on-ramp, and it never hiccups.  But since load current is low, like 100mA, I am not big on the idea of having a high OC current limit, like 2A.

4.  I increased on-ramp time from 5msec to 10msec, while keeping OC fault current limit at 1A.  It still hiccups about the same number of times.  So increasing to 10msec on-ramp time does not help OC fault tripping.

5.  I have no way to measure current in inductor (800KHz) but I did estimate it.  My estimate is that the inductor ripple current is about 1.1 Amps.  This seems high to me, which is why I am asking if that could be why it is tripping the OC fault limit, and if I should increase my inductance?

Thanks for the help,

Jim

 

 

   

 

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Nishanth
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100 solutions authored 10 likes given 100 replies posted

Hello @Jim_Brady ,

Thank you for the data and waveforms.

The recommended minimum inductance value is 1.6uH for 12V input and 1 to 1.5V output at 800Khz as shown below.Nishanth_0-1680590515049.png

Kindly increase the inductance value and verify.

Regards,

Nishanth

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Nishanth ---

Yes, I think my inductor value is too low, and I will get a few sizes of inductors and test.  1 amp inductor ripple current is too large when I am only drawing about 100mA max.  This will take some time to get parts and test.

Thanks,

Jim

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Nishanth
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Hello @Jim_Brady ,

Thanks for the update.

Let me know the result once you complete the testing.

Regards,

Nishanth

 

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