LM8365: Brownout function issue with Micropower Undervoltage-Sensing LM8365BALMF27/NOPB

Hi,

Immediately I notice that the RESET pin of LM8365 in your schematic is pulled up to 15V, which violates the absolute maximum rating of the device. We have a range of high voltage supervisors that will likely be a better choice for this application. A device such as TPS3842 or potentially TPS371K-Q1 may be more appropriate for this application.

I do not have a clear understanding of the application, are you able to provide a more complete schematic showing how LM8365 is connected to the rest of the circuit? Additionally, oscilloscope captures showing both the input and reset pin of LM8365 will be helpful.

-Henry

Hi Henry 

Thank you for your mail, i found Reset pin voltage maximum is 6V so I updated with voltage divider, i ll take forward as you suggested high voltage ic in further steps , please check the schematic as you requested

Also captured the oscillasope

Top one is at reset pin diode output

Bottom one is at 2nd pin 

If i add 0.1uf at C31 while  the voltage dips test  at 10 ms fails ic UCC28180D.

Hi,

We are still looking into this issue and will have a response by Monday (Pacific time). In the mean time are you able to provide oscilloscope captures with the 0.1uF C31 capacitor?

-Henry

Hi,

Please find attached oscilloscope capture for capacitor C31 changed to 0.1uf 

Input voltage 210 VDC Approx

Hi

Please find the capture as you requested, C31 =0.1uf, Vin=218V dc , R15=80k.

With C31

Without C31

With C31

Hi,

Sorry I should have clarified, I would like to ensure that the LM8365 is functioning properly completely on it's own, in a configuration similar to what is shown in the datasheet:

Are you able to test the above configuration with C_D = 1uF, sweeping V_IN below 2.7V and back above 3V to ensure that the device performs similar to what is shown in figure 1 of the datasheet?

Thanks,

-Henry

Hi

In this i changed the Pullup resitor to Vin 680K R16  , Changed C33 1uf , Previuos test was with 0.1uF , sorry for this mistake.

i have checked the test circuit without Gate resitor 10R , the circuit works well.

Below image is without PFC mosfet gate resitor

While gate resistor Connected it seems like this, >2.85V Vin 

Vin Below<2.75

Thank you for the additional details.

From the oscilloscope captures, assuming that the yellow trace is the input and green is the reset output, it looks like the LM8365 is in fact performing correctly. When the input drops below 2.7V, the reset asserts (goes low). When the input rises above 2.7V again, the reset de-asserts (goes high) after a delay. Do you expect different behavior from the device? If so, please explain.

-Henry

Yes yellow is Input and green is reset output, 

Yes LM8365 works correctly with out PFC turnrd ON, means i removed Mosfet gate resitor.

below imgage shows clearly there is multiple reset if i connec Mosfet gate resitor (PFC).  need solution for this !

Hi,

I'd like to clarify that the LM8365 is working as expected in the latest oscilloscope capture you've sent. I've created a timing diagram to explain the behavior more clearly.

At time t₁, when the input voltage is below 1V, there is not enough voltage to pull-down the reset output, so it will be a logic high. Once the input rises above 1V but is below 2.7V (t₂) the reset output will assert, pulling down the reset. Then when the input rises above 2.7V (t₃), the reset will release after ~1.2s. Once the delay has elapsed (t₄), the reset goes high, which seems to be causing the input voltage to drop and therefore the reset asserts again (t₅). After a short period, the input rises again (t₆) which causes the reset to release after ~1.2s, and the cycle repeats.

Since the LM8365 is working as expected, there is not much more support I can provide in this thread. I recommend creating a new thread related to the UCC28180D if additional assistance is required.

Thanks,

-Henry