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AMC1200 and motor phase voltage measurements

Other Parts Discussed in Thread: ISO124, AMC1200, AMC1301

Hello,

I need to measure a phase-phase motor voltage (U-V) with a F28335 DSP, including a galvanic isolation and bandwith > 50kHz.

As I already used the component, my plan was initially to use the ISO124, but then I remarked that it does not permit to measure a differential voltage (given that Vin is referenced to GND1 ; maybe I could eventually connect the GND1 to my "V" phase, but I don't like this solution) --> can anybody confirm that ISO124 is not well adapted for my application ?

So, I found the AMC1200 that is a fully differential voltage measurement amplifier, but I would have any questions concerning how we shall use it :

- Component supply (cf. datasheet figure 33 page 16) : the component will be supplied with +5V ; which resistor value shall I use (named R1 on fig. 33) ? what are the diode characteristics?

- Component supply : shall I supply the component in +5V/GND or +5V/-5V?

- Differential voltage measure : my motor phase voltage value will be around +/-65V ; is it ok to use a resistor divider to decrease the voltage to +/-250mV ? We need a good precision, so is it ok if we reduce so much the voltage, including the DSP ADC precision too ?

- Connexion to the ADC input : on §8.2.1.2 page 16, it is indicated I can connect the ACM1200 output directly to the DSP ADC input (0-3V), so I dont need to add any op. amp. to apply any offset ? I simply connect "VOUTP" to the ADC input, and "VOUTN" to the DSP GND (DSP GND will be connected itself to GND2 of AMC1200) ?

Then, if you know a component that could be better than AMC1200 for my application, please let me know !

Thank you in advance for any advise you could provide me,

Best regards,

Julien

  • Hi Julien,

    The AMC1200 does not tolerate a negative supply, you would have to power it from 5V to GND1, where GND1 can be floating at a high voltage level (i.e. referred to your V phase). You can use a voltage divider, but the 'shunt' should be as small as possible. You can also take a look at the AMC1301, it has a slightly different input stage and tolerates large shunts better than the AMC1200 does. The output of the AMC1200 (and AMC1301) is fully differential as well, so shorting VOUTN to GND is only going to cause excess power consumption. I am not sure if your F28335 has a differential ADC input, but if it does not, you can simply leave VOUTN floating.