UCD90320: Extending internal reset time

Hi

what do you mean internal reset time? could you please provide a GUI snapshot to show it?

Regards

Yihe

Hi Yihe,

Below is an extract from the UCD90320 datasheet. The way I translate this is that it takes about 9 ms to 11.5 ms for the sequencer to come out of reset once the reset line is asserted. I would like to find a way to extend that time if possible. 

I'm facing an issue where I have a 3.3V rail that does not decay to less than 200 mv once a sequencer reset is asserted. This rail then violates one of the criteria of one of the chips I use on the assembly. So, I would like to extend the delay of the sequencer coming out of reset to allow this 3.3V rail to decay to below 200mv before enabling the rail again. Based on the plots I took, if I can delay the sequencer about 450ms at the moment the rest line is asserted that will solve the problem I have.

I understand, there are many other ways to change hardware to allow this rail to decay to 0 V. But I'm no allowed to make dramatic changes on the circuit, since this assembly is mature and already int he field and etc,. So, my goal is to find out if I can modify the sequencer image or perform minor changes the sequencer level that can do the trick.

Thanks again and I look forward to your feedback. 

Regards,

Ali

Hi,

No, I'm not toggling 3V3 of the UCD90320 to force reset. The UCD90320 is powered by 3V3 Standby that is always on. I toggle the RESET_N pin (Active low) to reset the sequencer. 

The 3V3 rail that I want to keep powered off longer is another rail called 3V3_BCM.  

Thanks

Ali

HI

Why do you want to reset the sequencer. we do not recommend it anyway.

Regards

Yihe

Hi,

I reset the sequencer, because the reset pin is connected to the watch dog device. And once the watch dog is asserted (Via Software Maintenace mechanism) it goes and toggle the sequencer reset pin. We use this method to be able to reset the entire module remotely via software commands. These modules are outside and hanged on poles and we need to have a remote way to reset the module without taking the entire power down in the field. 

Often time if the module is stuck in a bad state, the watch dog gets triggered after specific time and reset the sequencer, in return the sequencer reset all the rails to reboot the module and clear the issue. 

Can you please tell me why you do not recommend reset on this UCD90320 device? Also, can you tell me please if you have other power sequencing devices that can do similar functions and support reset?

Thanks again and I look forward to your feedback,

Thanks

Ali 

Hi,

Thanks again for the feedback. Can you please send me the most recent copy of the UCD90320 datasheet? A link of the datasheet will do. The datasheet that I have shows section 7.2 is the ESD Rating.

Thanks again,

Ali

Thanks again,

Can you please tell me from where this text extract you sent earlier came from? you may send me the link if you can. I do not see it in the datasheet.

Thanks

Ali

Hi again,

I hope all is well. I'm looking to modify the existing sequencer reset design per your recommendation and have question. 

I'm connecting now the output of the external watch dog to the PMBUS_Control Pin to reset all the rails when the watch dog asserts. The question I have for you, Can I pull the RESET Pin high to the 3.3V_StandBy? 

Thanks

Ali

Hello again,

on the UCD90320 datasheet there is very brief description of the use of the PMBUS_CNTRL line. Is this signal active high or low? I want to use the PMBUS_CNTRL signal like you have suggested to reset all the rails via the watchdog, but I want to make sure I drive the correct signal to the PMBUS_CNTRL line. 

Thanks again for your assistance,

regards

Ali