OMAP-L138 power up sequence

Hi

Michi Yama said:

Does this mean that OMAP-L138 can allow ramp tim for 3.3V until maximum 10ms. And is the longer time than 10ms out of spec for OMAP-L138? Is there any spec for maximum power-up time?

There is no votage ramp rate requirement (as mentioned in the datasheet),  only the requirement for power sequencing and ensuring that the LVCMOS supplies
operated at 3.3V (DVDD3318_A, DVDD3318_B, or DVDD3318_C) never exceed the STATIC 1.8V supplies by more than 2 volts. No specification on the total power up time, as long as the sequencing is maintained.

Michi Yama said:

2) During the DVDD18 is ramping up, DVDD3318(3.3V ) supply is cut off  at the moment by external circuit. At this time, DVDD18 increase to near 2.7V at the moment.

The above is one experiment.  is this codition allowed for OMAP-L138?

Sorry, I do not understand this question? Perhaps plots for this power up test would be helpful. In general you would not want to have any 1.8V devices on the board to exposed to 2.7V for long period of times. If the application requires, powering up and down (compared to just powering up one time and remain on forever) than additionally it is not a good idea to expose 1.8V devices to prolonged periods of 2.7V. It is also not recommended to expose the device to a condition where Core and 1.8V supply is one and 3.3V is not on for prolonged period of time.

Hope this helps.

Regards

Mukul

Dear Mukul-san,

Thank you for your reply for my questionnaire.

I would like to explain regarding 2).

Our customer added the protection circuit  to their system. This circuit cuts off 3.3V supply when DVDD18 is increasing as it shows on errata.

However, as to their measurement,  DVDD18 increases up to 2.7V  approximately for a split second. In other words,  customer's additional protection circuit can't  protect DVDD18 increasing by 3.3V leakage perfectly. Is this allowed for OMAP-L138?

Please advise me again.

I appreciate your quick reply.

Best regards,

Michi

Michi Yama said:

However, as to their measurement,  DVDD18 increases up to 2.7V  approximately for a split second. In other words,  customer's additional protection circuit can't  protect DVDD18 increasing by 3.3V leakage perfectly. Is this allowed for OMAP-L138?

This does not sound like desired behavior. My understanding is that this is a consumer application, and if that means that the application will go through several power up and down cycles during its life time you are exposing on board components that should get a nominal 1.8V to a 2.7V supply. This is not recommended.

I would recommend that your customer investigate the other workarounds listed to work around this issue if the caps are not working. I would recommend working with an analog FAE in your region to see if they can make additional recommendation on the power supply design to work around this issue.

Regards

Mukul

Hello ,  Michi  asked me to talk about workaround with customer

I had asked customer to change the power sequence to  change 3.3V comes last after 1.8V is OK.

Below is the  result of  customer's work around.

How do you think this chart?  ( Customer hope to get your approval)