PMIC PCA9450 Buck and LDO Reverse Current Protection

[zingae]

I am designing a momentary backup power solution for the iMX8 Nano powered by PCA9450B. The goal of the backup power is to keep the iMX running long enough to move things around in non-volatile storage.

While normal operation would have the PMIC powered with Vin 5V, the backup situation would use 3.3V (regulated supercap) as an input voltage to the PMIC. The PMIC is spec'd to handle Vin down to 2.7V.

2 questions...

1) If the PMIC Vin is below the dropout voltage of an internal LDO or Buck, does the internal regulator just safely turn off on its own? Or is it required to disable the regulator with an I2C command? Specifically a 3.3V output LDO or Buck in the PMIC while PMIC Vin is reduced to 3.3V.

2) Is there any reverse current protection on the Buck and/or LDO outputs of the PMIC making it safe to apply 3.3V to the PMIC output (Buck 4 or LDO) while the PMIC Vin is only 3.3V and the regulator is not running either due to it being shutoff due to Vin being below dropout voltage or the regulator being disabled in the registers? I do see the Limiting Values section of the datasheet that says the voltage on the output pins should not be too much higher than the input, so technically the applied voltage to the output would still be within spec, even if the internal regulator is off.

Thank you!

[JorgeCas]

Hello, I hope you are doing well.

1) If the PMIC Vin is below the dropout voltage of an internal LDO or Buck, does the internal regulator just safely turn off on its own? Or is it required to disable the regulator with an I2C command? Specifically a 3.3V output LDO or Buck in the PMIC while PMIC Vin is reduced to 3.3V.

Yes, the internal regulator just safely turn off on its own when VSYS falls below POR threshold.

2) Is there any reverse current protection on the Buck and/or LDO outputs of the PMIC making it safe to apply 3.3V to the PMIC output (Buck 4 or LDO) while the PMIC Vin is only 3.3V and the regulator is not running either due to it being shutoff due to Vin being below dropout voltage or the regulator being disabled in the registers? I do see the Limiting Values section of the datasheet that says the voltage on the output pins should not be too much higher than the input, so technically the applied voltage to the output would still be within spec, even if the internal regulator is off.

Yes, when regulator is working, the protection is always ON, the output will drop and after remove Over current condition it will recovery.

Best regards.

[zingae]

Hello

Both of those answers do not seem to understand my questions. So more specifically...

1) If INB45 is 3.3V or lower, will Buck 4 turn off safely without needing to actually disable it by setting register value?

2) If LDO5 is set to 3.3V and INL1 is 3.3V or lower, will LDO5 safely turn off without needing to actually disable it by setting register value?

3) If Buck 4 and LDO5 are off (either through under voltage lockout condition or disabling in register), it is safe to externally apply 3.3V to the outputs of those regulators?

[JorgeCas · Accepted solution]

1) 2) Yes, it will turn off safely without needing to actually disable it 

3) It should be safe to to externally apply 3.3V to the outputs but, I suggest you use a diode to block any reverse current if you want to be sure.

Best regards.

[zingae]

Thank You!