RT1176 PMIC_ON_REQ goes low after 5mS

[mckaylund]

We are currently verifying that our design meets the power up sequence per the reference manual.  We are bypassing the internal DC/DC and all power rails come up in the correct sequence.  However, we have an intermittent issue that occurs sometimes during a brief power cycle.  The root cause appears to be the RT1176 "PMIC_ON_REQ" going low, about 5 mS after "VDD_SNVS_IN" goes high.

I can't seem to find anywhere in the reference manual that explains the cases when "PMIC_ON_REQ" would go low.  There is one mention of when the "DCDC_IN" goes below 2.6V that will cause “PMIC_ON_REQ to go low.  However, "PMIC_ON_REQ" still goes low and stays low even though “VDD_SNVS_IN” and “DCDC_IN” have remained stable throughout powerup. 

[jingpan]

Hi @mckaylund ,

ON/OFF is used to switch PMIC_REQ_ON to control power modes. A 4.7-kΩ to 10-kΩ series resistor can be used when the current drain is critical.

Regards,

Jing

[mckaylund]

Could you expound on your comment about the relationship between ON/OFF and PMIC_REQ_ON?

I have hardware that more consistently shows PMIC_REQ_ON going low after 5mS.  How is the ON/OFF signal linked to the PMIC_REQ_ON dropping low after 5mS after initial power-up?  I haven't seen any specific mention of this behavior related to power sequencing.  The consistency of the 5mS seems like the outcome of some logic rather than a transient voltage/current blip on the ON/OFF or PMIC_REQ_ON. 

I've included two oscilloscope screen captures of our power sequence which also includes the ONOFF signal.  In one capture, I have tied ONOFF to ground via a 6.6K ohm, and the other screen capture is with the ONOFF left unconnected for the MCU internal pullup control.

Could you clarify where the series resistor should be placed: ON/OFF or PMIC_REQ_ON?