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AMC1306E25: AMC1306X and TIDA-00914

JJ
Prodigy 20 points
Part Number: AMC1306E25
Other Parts Discussed in Thread: LM3480, TIDA-00914

Hi Ti ,

In the circuit diagram of TIDA-00914, when the AMC1306 is used for current sensing, an LDO(LM3480) is employed between AVDD and AGND to serve as the power source for the floating terminal. However, the voltage at the floating point is equal to the VDS (drain-to-source voltage) of the lower-side MOSFET. In a system with a voltage of 200V, this means there will be a minimum floating voltage of 200V. You might wonder why a standard LDO can be used in this scenario, especially since LDO datasheets typically do not specify restrictions on the floating voltage at the GND pin. I would like to inquire about the principles behind why this setup doesn't encounter issues.

The second question I would like to inquire about is whether, if we do not consider the impact of resistor-related power, choosing the +/-250mV variant of the AMC1306 would result in better noise immunity compared to the +/-50mV variant.

Thanks,

JJ

  • 0
    TI__Mastermind 48620 points

    Hi JJ,

    I support the AMC1306 and other isolated data converters - I am not an expert on LDO operation. However, I do not see a reason that an LDO would have an issue with a floating voltage for GND. The LDO will only see the differential voltage between the input and GND pin of a few volts. 

    For the second question, the common-mode rejection ratio between +/-250mV and a +/-50mV part is about the same. However, if there is a static amount of noise in the system, then a larger fundamental signal (+/-250mV vs +/-50mV) could result in a higher signal to noise ratio. The main reason to consider a +/-250mV vs +/-50mV device is the amount of current to be measured and the resulting power dissipation in the shunt resistor.  

    This FAQ has a link to our collateral: https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1164993/faq-isolated-data-converter-collateral-overview