i.MX RT1020 DCDC not restarting after voltage dip

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i.MX RT1020 DCDC not restarting after voltage dip

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fredrikeriksen
Contributor II

We have a board running RT1020.

The main power structure is 12V -> 3.9V SMPS, then this 3.9V is going through and LDO to 3.3V and then to RT1020.

See schematic attached for how it is connected.

The problem is that if we dip main voltage below the point where the SMPS drops and thus the 3.3V signal starts to flicker, and then increase voltage back up, the DCDC of the RT1020 does not start. All other voltages are fine.

Any thoughts? Could it be something regarding the RC circuit on the DCDC_PSWITCH for instance?

Any help if greatly appreciated.

Thanks.

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wj_ueos
Contributor II

DCDC_PSWITCH has to be brought below 0.5V in order for the DCDC to restart (it needs to see a low-to-high transition on the pin, not just a high level). I have seen the same behavior on RT1020, 50 and 60 series (identical DC/DC I would assume).

An external reset/supervisor controller is one way to solve this, pulling the pin low as long as the 3V3 isn't OK.

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jeremyzhou
NXP TechSupport
NXP TechSupport

Hi Fredrik Eriksen,

Thank you for your interest in NXP Semiconductor products and
for the opportunity to serve you.
After going through your statement, I'm still a bit confused.
What's the exact meaning of the 'the DCDC of the RT1020 does not start', whether it means that the DCDC doesn't output the voltage ever.
In further, I was wondering if you can present the vary of the different voltages during the testing of voltage dip, and does it cause POR reset event?
Looking forward to your reply.

Have a great day,
TIC

 

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