TLV809: TLV809K33 can't work normally

Hi,

Can you tell me the resistor value that you are using on PR41?  Looking at the schematic, PR41 will affect the de-asserting of /RESET.

Ben

Hi,

The startup transient current for the 809 maybe an issue that is causing your application to not function.  Can you reduce the PR39 and PR40 by half (PR39 = 50Kohms and PR40 = 22.1Kohms) and place a 0,1uF cap on U8_IN?

Ben

Hi,

I have change PR39 and PR40(PR39 = 4.75Kohms and PR40 = 1.8Kohms) and it has 0.1uF on the schematic original.

When i change resistor abvoe, the schematic is normal now.

So it's the value of resistor too lager cause the current too small right?

Thank you.

Hi,

Yes, the the Iq current for the 809 is listed as 9uA.  If PR39 is 100kohms, the drop across the resistor of PR39 is 900mV.  Therefore the voltage at U8_IN is 3.3V-0.9V = 2.4V which is not high enough for the TLV809K33.  I hope this answers your question.

If I have answered your questions to your satisfaction, please click on "resolved" to close the thread.

Ben 

Hi Ben,

I am confused for your reply.

The input voltage of the schematic is 12V. It is not 3.3V.

Hi,

I apologize for giving you the wrong information.  Because the 809 has an Iq current of 9uA, it will create a 900mV drop across PR39.  Therefore, instead of seeing 3.3V at U8_IN, you will actually see a lower voltage of around ~3V at U8_IN.  In my last post I forgot about the voltage divider PR39 and PR40.  I hope I have answered your question.

Ben