| 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 |