• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 63 subscribers
  • Views 1129 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS3808G01 Cold ambient performance

Paul Schoenke
Expert 1375 points
Other Parts Discussed in Thread: OMAP-L138

Hello TI:

I have a technical/application question on the TI TPS3808G01 Supervisory IC.  We currently use this part on a OMAP-L138 based design as the main or master reset generating IC.  We are experiencing a cold temperature boot problem of the L138 which is related to this IC.  We believe we have found a solution to the problem, but were looking for confirmation the solution is ok as related to the application of the TPS3808G01.  If so, below is a summary of the details.

Attached is a snippet of the Reset circuit.  Note the TPS3808G01 Reset output pin is pulled-up to 3.3V with a 4.7k Ohm Resistor.  The Resistor is located at the IC and is connected to 7 circuit loads across our PCB design.

As mentioned, we discovered a problem where the L138 would not boot at cold ambient temperatures below 0C.  Upon investigating we discovered the Reset signal did not have a sharp low to high transition, but instead a slow stepped transition from low to high coming out of reset.  We traced the problem down to a prior design change where an 8th load was added from a change to an L138 Boot Serial SPI Flash Memory IC with a Reset input.  With some further investigation and testing we could eliminate the slow, stepped Reset signal, and the thus the cold temperature boot problem, with a change to the Resistor pull-up value to 1.5K Ohms from 4.7k.

In reviewing TPS3803G01 data sheet Page 4 Table and Page 8 Section 8.3.4, it mentions that the Reset output pull-up Resistor value should be no smaller than 10k Ohms.  However, from what is spec’d in the data sheet, it appears 1.5k Ohm is ok since it does not exceed the 5mA absolute maximum Reset pin current noted on Page 5 Section 7.1 and Page 9 Figure 8. 

Therefore, can you confirm a 1.5k Ohm pull-up Resistor can be used on the Reset output pin of the TPS3803G01 without any problems?

Any feedback or input is welcomed and appreciated!

Thanks again!

Paul

  • 0
    TI__Expert 6975 points
    Hi Paul,

    You should be able to use the 1.5k resistor because you are below the recommended max of 5mA and should have a Vol of around .2V. The part of the datasheet that is talking about the 10k Ohm pull-up resistor is there to ensure that part still issues a logic low (Vol). If the resistor is changed to a lower value resistor then you need to ensure that it will still issue a logic low.

    Additionally because the part has an open drain reset the only thing that will delay it from coming up at cold are the value of the resistor as you mentioned and the supply current of the power supply. If the power supply is unable to provide enough current to bring the rail up at these temperatures then that will also cause similar problems to what you are seeing.

    Best Regards,
    Mark