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LT8609EMSE#PBF Step down regulator

Question asked by rikr09 on Apr 19, 2018
Latest reply on Apr 19, 2018 by DONGW

Hello, 

 

Is my first time with the LT8609 regulator and i'm really disappointed. I copied exactly the same design of the typical application described on the first page of it Datasheet, and it doesn´t really works as expected

 

My VCC is an wall adaptar of 12V @ 2.1A.  

The only circuit to which i'm supplying voltage is a Raspberry Pi Zero W. According with the current measurement there is about in average around 150mA and the voltage of the source down until 3.5V restarting the Raspberry. At this point, all is a mess and a scam, because as you can see on the following image the ouput supports supposedly  2A at 5V.

I selected this regulator because i have another projects with the LT3995EM and this have been working perfectly always, but i thought that 3A output would be too much for this project. 

 

So, what i have done:

  • First, i changed the 187K for one of 182K because with this first the voltage output is 4.96V, not 5V. 
  • I changed the RT resistor to a 182k and the Raspberry is working good without restarting; but, the output voltage down to 4.65V and is unstable. I'm measuring some ADC points and the values are oscillanting because of this behavior. 
  • Now, and trying to fix the unstable output voltage i change the RT to 47K and the voltage mantains stable in 5V but once i turn on the WIFI of the Raspberry, this do not work as expected, i suppose this is because that the source does not supply enough current. 
  • Trying to find the solutions to my problems i follow the design of my LT3993. This can be detailed on the following image. So i punt the SYNC pin to GND. The PG resistor i removed it, and the SS pin os to GND across a 10nF capacitor. But it didn't solve my troubles. 

Finally in order to discard the regulator, i did an adaptation and i connected with wires the LT3995 supply source (as detailed on the image above) to the main board where i have the Raspberry, and everything works fine! Current and voltage stabilization. But THIS IS NOT MY SOLUTION.

So i would like to you help me to solve this trouble with the LT8609, i dont know what else to do.

Thanks!!!

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