Electronics > Projects, Designs, and Technical Stuff
How can a chip (HX711) work without a ground pin connected?
<< < (3/4) > >>
wraper:

--- Quote from: SiliconWizard on June 14, 2018, 05:06:21 pm ---
--- Quote from: edavid on June 14, 2018, 04:29:02 pm ---AGND is not necessarily a power connection.  It could be a reference voltage that is only connected to some MOSFET gates, so no current is drawn.

--- End quote ---

So there would be absolutely no ground connection on this chip?  :wtf:
As per the datasheet, it IS meant to be connected to ground.

--- End quote ---
There is GND connection to IC, digital GND. The issue is that resistive bridge is connected to AGND but not actual GND, therefore is powered through AGND pin.
SiliconWizard:

--- Quote from: wraper on June 14, 2018, 05:37:47 pm ---
--- Quote from: SiliconWizard on June 14, 2018, 05:06:21 pm ---
--- Quote from: edavid on June 14, 2018, 04:29:02 pm ---AGND is not necessarily a power connection.  It could be a reference voltage that is only connected to some MOSFET gates, so no current is drawn.

--- End quote ---

So there would be absolutely no ground connection on this chip?  :wtf:
As per the datasheet, it IS meant to be connected to ground.

--- End quote ---
There is GND connection to IC, digital GND. The issue is that resistive bridge is connected to AGND but not actual GND, therefore is powered through AGND pin.

--- End quote ---

What is the digital GND pin on this IC?
wraper:

--- Quote from: SiliconWizard on June 14, 2018, 05:45:11 pm ---What is the digital GND pin on this IC?

--- End quote ---
Oops, yep there is no digital GND pin, it's powered through protection diodes on X1 and Rate pins.
Tonn:
The board works well with both E- to ground or not. It seems the HX711 is not much affected by the diode voltage drop.
Accuracy or noise may be affected, but I don't have the means to verify that.

It seems I can call this one solved. Very educational.
@NiHaoMike: nice catch; you made me look for a diode, not just connection or resistance.

Everyone thank you very much for your help.
Tonn



Dave_PT:
Sorry to come dig up this topic.

But I have some problems with these chinese boards from a project point of view  :o.

Clearly they have design mistakes (GND, etc...). But can someone explain me the feedback resistances?
Why they use R1=20k and R2=8.2k?
To get a AVDD of 1.77V?  :o Why?


[EDIT]
Vbg=AVDD*R2/(R1+R2)
AVDD=Vbg*(R1+R2)/R2 -> the datasheet equation is wrong.



Another thing, has anyone used the oscilloscope to measure the AVDD? Can anyone explain me why the AVDD comes up as a "square wave" of about 50Hz?

Actually I can use the IC to take measurements ... but I can not figure out how the analog supply regulator works.


Thank you all
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod