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do you need decoupling cap for Bandgap reference voltage?

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windsurfer

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For instance, the VBG is 1.2V, do we need to connect this node to decoupling cap to VDD, say 3.3V? I am afraid the cap will become an AC path for the VDD noise to couple into VBG. Any comments
 

btbass

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Study the data sheet, depending on the load, some bandgaps need a cap for stability.
 

hung_wai_ming@hotmail.com

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It depends.
If you use dominant pole compensation for bandgap, you may need a cap to connect bandgap output to either VDD or VSS. Most of the time, we connect to VSS as VDD will couple AC noise to bandgap node.
 

windsurfer

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Re: do you need decoupling cap for Bandgap reference voltage

But for some cases, the ground bouncing could be very serious. Connect decoupling cap to ground would also couple AC noise. How can we deal with it?
 

hung_wai_ming@hotmail.com

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Ground is the lowest impedance on the chip and you need to connect a large cap externally for maintaining low noise low impedance ground.
 

windsurfer

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Re: do you need decoupling cap for Bandgap reference voltage

I see what you are saying. But there is a bond wire inductance from internal ground to external PCB gnd and big cap, so it will still have ground bouncing internally. But as you said, we could have a huge decoupling cap for the gnd inside the chip.

thanks!
 

watersky

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why need it a cap? If you want to compensate it for stability, you can find other way to do it.
 

abcyin

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Re: do you need decoupling cap for Bandgap reference voltage

watersky said:
why need it a cap? If you want to compensate it for stability, you can find other way to do it.

for example, which way?
 

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