AMC3330: HGND to be derived from the voltage divider circuit

rajesh beesetty

Part Number: AMC3330

I have a requirement of measurement of 3 phase unbalanced voltages. I found AMC3330 is a right IC that works for my application. But, I see two circuits, one in the datasheet, other in the sbaa553 (link2). In both the circuits its recommended to measure the voltage(+/-1V) across the resistor that is connected in the middle of the potential divider. However, in sbaa553 the HGND is derived from the voltage divider. Would this practice is recommended? Secondly, If the phase voltages are to be measured, still the HGND derivation from the voltage divider is recommended?

Finally, can I tie all the DIAG pin and give to the micrccontroller digital pin?

Regards,

Rajesh BN.

over 1 year ago

0 Alexander Smith over 1 year ago

TI__Guru 54562 points

Hi Rajesh,

Connecting HGND to the sensing resistor ensures that the voltage remains within the common-mode input range of the device regardless of transient voltages.

I do not fully understand what you mean by "derived from the voltage divider". The schematic shown in SBAA553 is recommended to cancel out the offset created by the input bias current flowing across the sensing resistor.

0 rajesh beesetty over 1 year ago in reply to Alexander Smith

Expert 1325 points

Sorry for the confusion. I meant, the HGND is connected at the voltage divider circuit. Moreover, it's connected at the midpoint of the sensing resistor. On the other hand, it is not the case in the data sheet recommended circuit. Would you recommend connecting HGND as shown in the figure?

0 Alexander Smith over 1 year ago in reply to rajesh beesetty

TI__Guru 54562 points

Hi Rajesh,

When measuring ph-ph voltages, the recommended circuit shown in SBAA553 should be followed to cancel the slight offset created by the input bias current flowing through the sensing resistor.

When measuring ph-nuetral voltages, this HGND connection in the middle of the sensing resistor is not necessary. VINN can be tied to HGND and VINP can swing +/-1V.

0 rajesh beesetty over 1 year ago in reply to Alexander Smith

Expert 1325 points

Thank you Mr. Smith for the explanation. I would like to know if I have to connect any ESD diodes at the input.

Regards,

Rajesh BN.

0 Alexander Smith over 1 year ago in reply to rajesh beesetty

TI__Guru 54562 points

Hi Rajesh,

Happy to help!

As long as the absolute maximum ratings are not violated, -6V, or 3.5V, no protection diodes are necessary.

0 rajesh beesetty over 1 year ago in reply to Alexander Smith

Expert 1325 points

Furthermore,

Would you recommend to use the same resistor circuit- using split resistors, while phase voltage measurement?

0 Alexander Smith over 1 year ago in reply to rajesh beesetty

TI__Guru 54562 points

When measuring ph-nuetral voltages, this HGND connection in the middle of the sensing resistor is not necessary. VINN can be tied to HGND and VINP can swing +/-1V.

0 rajesh beesetty over 1 year ago in reply to Alexander Smith

Expert 1325 points

Even it's not necessary, it will make any harm to the signal, say, distortion?

0 rajesh beesetty over 1 year ago in reply to Alexander Smith

Expert 1325 points

Since I am at the schematic design stage, I may be controlling phase/line Voltage in the future depending upon the convenience. I would like to keep the connections as it is, while changing the input terminals to change the phase voltage measurement to line voltage measurement. In that case, split resistor Voltage didivider mesures the phase voltage too. Would it be an issue? If not, is it an advantage?

Secondly, I would like to know if HGND supposed to be a track or plane on the PCB for better results?

+1 Alexander Smith over 1 year ago in reply to rajesh beesetty

TI__Guru 54562 points

I think that should be fine, if it allows for increased flexibility - I would view it as an advantage.

If testing for radiated emissions or EMC, a trace for HGND is recommended: https://www.ti.com/lit/an/sbaa515a/sbaa515a.pdf?ts=1699542864179

0 rajesh beesetty over 1 year ago in reply to Alexander Smith

Expert 1325 points

Thankyou for the link... Are these guidelines applicable to AMC3330 too?

0 Alexander Smith over 1 year ago in reply to rajesh beesetty

TI__Guru 54562 points

Yes, all AMC33xx devices.

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AMC3330: HGND to be derived from the voltage divider circuit