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AMC1306E25: Where to place the shunt sensor and can 3 ISO adcs have the same PSU

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Prodigy 50 points
Part Number: AMC1306E25

Hi, 

I'm making a 3 phase buck converter and I need 3 phase current measurements (1 for each phase) and 1 voltage measurement (output voltage).  

In my current schematic I have it set up so that the current measurement is between the switch and the inductor. I had problems with long delta sigma lines to the uP.  It got me thinking that large (to 900V ) voltage swings at the switch node are not going to be good for good measurements. 

1) Placing the 3 current measurements between the inductors and output capacitor would be batter because of the stabler CMV, right? 

2,3) Could I then use 1 ISO power supply to supply all 4 insulated measurements? The 3 currents and the voltage sensing are going to have the same "ISO GND" that will be the V+ off the capacitor.  For the voltage measurement I will then have to use the first resistor in the resistor divider ladder. Now I have it sensing form the middle of the resistor divider ladder, this was, in past experiences better. Would this be a problem?

I know if I use 1 power supply I will have to make good decoupling, maybe some ferite beds for each ADC to keep the power supply noise down. 

Best regards, 

Marko 

  • 0
    TI__Guru**** 168695 points
    Hi Marko,

    Without seeing your schematic and assuming the three phase currents are all referenced to the same point (i.e. the same 'iso gnd' you mentioned above), you could use a single power supply for all three of the AMC1306E25 devices. The voltage measurement would also have to be referred to the same ground in order to use the same power supply. You would need to observe the operating common mode voltage limitations of the AMC1306E25 which is no more than the AVDD - 2.1 V referenced to AGND (see Vcm in section 7.10 of the datasheet) .