AM1808: 3.3V does not drop when power is turned off

Hi,

I have assigned your query to our expert. Since the team is out for holidays, expect a response post New year.

Apologies for the delay.

Best Regards,

Suren

Hello Kishimoto Kazuma

Thank you for the query.

Kishimoto Kazuma said:

In AM1808, I have a 3.3V power line with about 1.4V left in it even though I have power-off.

Can you please verify if there are any input applied (voltage level) that is higher than the supply rail that is causing leakage, 

Regards,

Sreenivasa

Hello Kishimoto Kazuma

Kishimoto Kazuma said:

n AM1808, I have a 3.3V power line with about 1.4V left in it even though I have power-off.
AM1808 has provisions for power-on, but no detailed provisions for power-off.
Is there a correct sequence of power lines to power-off?

Checking if you have had a chance to review the errata.

2.3.7 

https://www.ti.com/product/AM1808

Regards,

Sreenivasa

Hello Kallikuppa Sreenivasa-san,

Thank you for your reply.

I have already checked Errata 2.3.7 and I believe it is about power ON.
I was talking about the 3.3V power supply not going to 0V and leaving 1.4V when powered OFF, do you think this phenomenon leads to errata 2.3.7?

Regards, 
Kazuma

Hello Kishimoto Kazuma

Thank you.

Kallikuppa Sreenivasa said:

Kishimoto Kazuma said:

In AM1808, I have a 3.3V power line with about 1.4V left in it even though I have power-off.

Can you please verify if there are any input applied (voltage level) that is higher than the supply rail that is causing leakage, 

Can you please verify the above.

regards,

Sreenivasa

Hello Kallikuppa Sreenivasa-san,

Thank you for your reply.

When the 3.3V power supply of AM1808 is turned OFF, it kills everyone above 3.3V.

Regards, 
Kazuma

Hello Kishimoto Kazuma

Thank you.

This is not the on-board supply. 

Please check if there are any external inputs connected to the AM1808 that have a signal when the AM1808 is off.

Regards,

Sreenivasa

Hello Kallikuppa Sreenivasa-san,

Thank you for your reply.

Sorry, my information was incorrect.
C4, D1 and D4, E1~E3 are pulled up to another 3.3V (3.3V_AL) even while the 3.3V supply (3.3V_IDL) of AM1808 is turned off.
Also, 5V (VDC_5V) on N19 slowly drops in voltage toward 0V over a long period of time (more than 10 seconds).

Regards, 
Kazuma

Hello Kishimoto Kazuma

Thank you.

You will have to review the implementation to see who is causing the leakage and make the required changes. (Since you have the design files and also the familiarity)

general note is - the inputs should not be available before power supply ramps.

Regards,

Sreenivasa

Hello Kallikuppa Sreenivasa-san,

The voltage remaining when trying to turn off the AM1808 power supply (3.3V_IDL) is as reported the other day.
Could you provide any comments?

>
C4, D1 and D4, E1~E3 are pulled up to another 3.3V (3.3V_AL) even while the 3.3V supply (3.3V_IDL) of AM1808 is turned off.
Also, 5V (VDC_5V) on N19 slowly drops in voltage toward 0V over a long period of time (more than 10 seconds).

AM1808 uses 1.2V and 1.8V in addition to 3.3V.
When turning off the AM1808, I try to drop 3.3V first, then 1.8V and 1.2V, but 3.3V does not drop. It is maybe caused by the leakage.
The reason the order in which power is turned off is as it is now is because the datasheet has a provision for power ON, but not for power OFF.
Going back to my first question, is there any provision for the order in which power is turned off?
Should I really drop the smaller power supplies first?

Regards,
Kazuma

Hello Kishimoto Kazuma

Thank you.

Kishimoto Kazuma said:

The voltage remaining when trying to turn off the AM1808 power supply (3.3V_IDL) is as reported the other day.
Could you provide any comments?

>
C4, D1 and D4, E1~E3 are pulled up to another 3.3V (3.3V_AL) even while the 3.3V supply (3.3V_IDL) of AM1808 is turned off.
Also, 5V (VDC_5V) on N19 slowly drops in voltage toward 0V over a long period of time (more than 10 seconds).

Do you see any of these signals causing leakage. Since you have the design information, i guess you are in a better position to review.

Kishimoto Kazuma said:

AM1808 uses 1.2V and 1.8V in addition to 3.3V.
When turning off the AM1808, I try to drop 3.3V first, then 1.8V and 1.2V, but 3.3V does not drop. It is maybe caused by the leakage.
The reason the order in which power is turned off is as it is now is because the datasheet has a provision for power ON, but not for power OFF.
Going back to my first question, is there any provision for the order in which power is turned off?
Should I really drop the smaller power supplies first?

If this is something that could be tested, i would recommend trying.

Regards,

Sreenivasa