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.
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
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?