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TPS63050: TPS63050 FB Question.

Expert 2485 points
Chun Youngsu

Replies: 4

Views: 274

Part Number: TPS63050

Dear TI Team,

I have a problem designing the TPS63050.

We would like to use a potentiometer in FB.
If you connect a FIXED resistor to R1 and connect a potentiometer to R2, it will operate normally up to 5V.
However, if you design R1 and R2 with the potentiometer below, the output will not rise above 3.4V.

If R1 and R2 are variable at the same time, I would like to know if the voltage and current of the FB fluctuate and cause a problem.
I want to know if there is a solution.

R1(RAW)

R2(RWB)

V_out

R_total

I_total

I_wa

I_wb

50.100KΩ

50.100KΩ

1.60V

100.2

15.97uA

15.97uA

15.97uA

68.850KΩ

31.350KΩ

2.56V

100.2

25.52uA

25.52uA

25.52uA

73.538KΩ

26.663KΩ

3.01V

100.2

30.00uA

30.00uA

30.00uA

77.444KΩ

22.756KΩ

3.52V

100.2

35.16uA

35.16uA

35.16uA

80.569KΩ

19.631KΩ

4.08V

100.2

40.75uA

40.75uA

40.75uA

84.475KΩ

15.725KΩ

5.10V

100.2

50.87uA

50.87uA

50.87uA

Thanks.




			

									
		


				
				
									

					
				

					
							

  

    
                  

        
          Expert
        2485 points
      

          
    
            
    
  

	
					
					
	

					
				Chun Youngsu
			
			







	
								
	
	




		
			

	


			

			
	
    
		




	
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          Genius
        13260 points
      
    
              
    
            
    
  
    
	
					
					
  
    
					
				Julian Hagedorn
			
			
    

    



    
	
    
		
	
    

    

		
		
		
				
		
    
						
    
				Hi Chun,
    

    
i would assume that VDDS_FET voltage is around 3.3V, correct?
    
The digital potentiometer port A max input voltage is usually equal to VDD. If you go higher the ESD protection start to conduct. 
    
In this case where VDD is 3.3V the TPS63050 output voltage would be limited to this.
    
Please ensure that the VDD of the potentiometer is >= the max desired output voltage or use the potentiometer only as "R2" between FB and GND.
    

    
Note that the accuracy of the potentiometer are typically in the +/-20% range, which will impact the TPS63050 output voltage accuracy.
    

    
I also see that only a single 10uF Cout is placed. Please ensure that min 10uF capacitance for all output voltages are used. Consider the DC-bias effect of the capacitor.
    

    
What is the application problem that you try to solve with this function?
    

    
regards,
    
Julian
    
			
    
									
    For more information on buck-boost devices have a look at ti.com/buckboost.
    

    
		
    

				
				
		
							
    
	
	
	

						
	

  
	

    

		
			
    

		




	
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          Expert
        2485 points
      
    
              
    
            
    
  
    
	
					
					
  
    
					
				Chun Youngsu
			
			
    

    



    
	
    
		
	
    

    

		
		
		
				
		
    
																		
    In reply to Julian Hagedorn:
    
															
    
				Dear Julian,
    

    
Thank you for answer.
    

    
Let's try changing Test the VDD of the potential meter to 5V.
    

    
application : Insulin pump
    

    
Thanks.
    
			
    
									
		
    

				
				
		
							
    
	
	
	

						
	

  
	

    

		
			
    

		




	
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          Mastermind
        26790 points
      
    
              
    
            
    
  
    
	
					
					
  
    
					
				Brigitte
			
			
    

    



    
	
    
		
	
    

    

		
		
		
				
		
    
																		
    In reply to Chun Youngsu:
    
															
    
				Hello Chun,
    

    
Please as well check the output capacitance as Julian mentioned.
    

    
Please check as well the transient performance for your system. The capacitor connected from FB to GND will make the transient response to load changes slower.
    

    
Please as well make sure that your system can survive the maximum output voltage on VDD_OUT. If the potentiometer opens the FB for some time, it could happen that the output voltage suddenly rises above 5.5V. For an analog potentiometer,  I would recommend to add a resistor divider for the highest secure voltage in parallel to the potentiometer because analog potentiometer sometimes open when the value is changed. I do not know if this can happen with digital potentiometer as well.
    
			
    
									
    Best regards,
    Brigitte
    

    For more information on buck-boost devices have a look at www.ti.com/buckboost
    
		
    

				
				
		
							
    
	
	
	

						
	

  
	

    

		
			
    

		




	
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          Expert
        7865 points
      
    
              
    
            
    
  
    
	
					
					
  
    
					
				Milos
			
			
    

    



    
	
    
		
	
    

    

		
		
		
				
		
    
																		
    In reply to Chun Youngsu:
    
															
    
				Hello Chun,
    

    
We haven’t heard back so we're assuming you were able to resolve your issue. If not, just post a reply below, or create a new thread if the thread has locked due to time-out.
    

    
Thanks,
    
Milos
    
			
    
									
		
    

				
				
		
							
    
	
	
	

						
	

  
	

    

		
			
    

	

		

		
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