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AD8334 Production
The AD8334 is an ultralow noise, quad channel linear-in-dB variable gain amplifier (VGA). Although optimized for ultrasound systems, it may be used as...
Datasheet
AD8334 on Analog.com

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ad8334

		
	
				

			

									
					    PowerStar143
					
							

            
            			
				
									
											
			
			
				
			
			
			    	
			                    
                
				                on Sep 17, 2026 
				
			
			
		

		
		                     
				
        		

		    
		    		    

		      		            		        
Category: Hardware

    		        		            		    
Product Number:  AD8334 

    		        		    		    

		    		    
		    			

			    
Hi ,




I have designed a Variable Gain Amplifier (VGA) circuit using the AD8334, bypassing the internal LNA section.


  Instead, I am applying an external differential signal directly to the VGA inputs (VIP1 and VIN1). The output of the AD8334 drives a THS4131 differential amplifier.


Currently, the AD8334 IC is overheating immediately upon power-up.


I have detailed my schematic layout below [or: attached the schematic details]. Could you please review the configuration and share your feedback on what might be causing the overheating?

			

			
									
		                             
                        

    

                                            
                 amplifiers
                
                                                    
                 hardware
                
                                                    
                 Variable Gain Amplifiers (VGA)
                
                                                    
                 ad8334
                
                                
            

    
    
		


				
				        
        		

			
						
									
												
			
			
                        
                                    
                        
                        
                        
            
			            
						
						
			
			
			
			
		


        
        
        
    
					

			





















	

	

					



			


				
	









	
    
	

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    •  Analog Employees  
    
            
						
                            
            
            				
            
                on Sep 19, 2026 9:09 PM
            
            
						
			            		
    
		
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    Hi  
    

    Thank you for your question. Let me check this internally with the team and review the available information. I will get back to you once I have an update.
    

    Best regards,
     Ian
    

    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
						
				
				
		
		
    
			
		
    
	
    

    

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    •  Analog Employees  
    
            
						
                            
            
            				
            
                on Sep 20, 2026 9:30 PM
            
            
						
			            		
    
		
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    Hi  

    After reviewing the schematic, we recommend checking the following:

    1. The LMD1 - LMD4 pins are left floating. These pins are connected to the LNA bias circuitry and should be bypassed to ground using 0.1uF capacitors, even when the LNA signal path is bypassed.
    2. Output clamp resistors are 100 ohms, which is below the values listed in Table 8 of the datasheet. Please verify the intended output clamp level and select the appropriate resistor values.
    3. Exposed pad must be properly soldered to PCB ground for heat dissipation.

    Could you also share the measured AD8334 supply current during power-up and confirm whether the overheating occurs with no input signal applied?

    Best Regards,
    Ian
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
						
				
				
		
		
    
			
		
    
	
    

    

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                on Sep 21, 2026 9:16 AM
            
            
						
			            		
    
		
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    Hi Ian,
    


    Thanks for your feedback and recommendations regarding the AD8334.
    I will measure the supply current during power-up and update you with the findings.
    Regarding the LMD pins: We are using a total of 16 AD8334 ICs on a fully assembled PCB. Connecting a 0.1 µF capacitor to each individual LMD pin  would require adding 64 capacitors using jumper wires. Instead of connecting individual capacitors for the four LMD pins on each IC, can I short the four LMD pins of a single IC together and connect them to ground through a single 0.1 µF capacitor?
    Additionally, I will remove the clamp resistor (allowing the default limiting level to revert to 4.5 V p-p), monitor the IC current and heating, and update you tomorrow.


    Thanks and regards,
    Keshav
    

    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
						
				
				
		
		
    
			
		
    
	
    

    

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