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ISO224: High Voltage High Side sensing with ISO224

chaitanyab
Intellectual 610 points
Part Number: ISO224
Other Parts Discussed in Thread: AMC1302, AMC1300, AMC3302, AMC3301, INA149, AMC1336, AMC3330, AMC1350, AMC1351

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Hi,

I am not able to find common mode voltage range for ISO224 in the datasheet. I want to use it for 900V System as a high side current measurement with shunt, can this chip handle high common mode voltage ? VDD1 and VDD2 will have more than 2kV isolation from my low voltage power supply. I thought the max common mode this chip can handle is probably VCC/2 like 6V.  Do we need VDD1 and VDD2 both isolated wrt to 900V in order to make this work? 

I am not sure whether this chip is meant for high side sensing for high voltage application, I see some high common mode voltage, isolation amplifiers are huge in size as against this for example AD210. Please comment.

Thanks,

  • 0
    TI__Mastermind 47595 points

    Hi,

    Since there are separate grounds, one for the high voltage side and one for the user-side you may be getting confused with what the voltage are measured with respect to. 

    When you say "VCC/2"  think you are referring to the common-mode output voltage, which is that output voltage when 0V is applied to the input. 

    I believe the specification you are looking for to verify that this device is capable of measurements in a high voltage application is the working voltage, specified at 1.5kVrms:

    This document may help with understanding our isolation specifications: https://www.electronicdesign.com/power-management/whitepaper/21130089/introduction-to-isolated-amplifiers-and-modulators

    What is the magnitude of the current to be measured? 

    We have other device with smaller input voltage ranges (+/-250mVm AMC1300, +/-50mV AMC1302) that are intended for current measurements to reduce the power dissipation in the shunt resistor. 

    We also have devices with integrated DC/DC converters such as the AMC3301 and AMC3302.

    We also have several cookbook circuits and design documents under the Technical Documentation section of the ISO224 product folder that may be able to help you. 

  • 0
    Guru 140200 points

    Hi,

    why not looking into section 7.6 of datasheet?

    Kai

  • 0 in reply to Alexander Smith
    Intellectual 610 points

    Hi,

    Where I am coming from is let's say INA149 it has high common mode input specification clearly shown and it is exclusively designed for high voltage applications in non-isolated environment.  Similarly is there any spec for ISO224 or is common mode  irrelevant here because of isolation?

    Is there any application note that shows high side (shunt in positive side of the battery/ not ground side) isolated sensing using Isolation amplifier similar to ISO224 with high voltage input?

    Like may be motor phase currents for high voltage motors?  for three phase current sensing how many isolated supplies are needed in that case? 

  • 0 in reply to chaitanyab
    TI__Mastermind 47595 points

    Hi,

    Like you said, the INA family of devices have a high common-mode input specification for high voltage applications without isolation. They have one voltage supply to power the device.

    Traditionally, the AMC and ISO family of devices have two voltage supplies to power the device. One supply on the high voltage side of the measurement and one on the user side of the measurement with capacitive isolation between the high voltage and user side of the device that communicates the measurement data. These devices do not have high common-mode input specifications like the INA devices because the entire high voltage side of the device floats with respect to the user side of the device, up to 1.5kVrms like I posted before. The common-mode input specification for the AMC and ISO family of devices is specified with respect to the high voltage ground and often only a few volts. Since the ISO224 has a single-ended input, the common-mode input specification is not relevant, however working voltage is the "common-mode input specification" if you are measuring with respect to the user-side ground. 

    The AMC1336 datasheet has a diagram similar to what you are asking for:

    The AMC1336 device is an isolated modulator with a +/-1V input, used for voltage sensing in this case. 

    The AMC1306 device is an isolated modulator with a +/-250mV input, used for phase current sensing in this case. 

    An isolated supply would be necessary for each phase current measurement. Another option is to use a device with an integrated DC/DC converter, eliminating the need for individual isolated supplies such as AMC3301, AMC3302 or AMC3330. 

    Devices similar to ISO224 are the AMC1350 and AMC1351, these devices have +/-5V and 0-5V input voltage ranges. 

    What is the magnitude of the current to be measured? 

    Devices with higher input voltage ranges are typically used for voltage sensing whereas devices with smaller input voltage ranges are typically used for current sensing to minimize power dissipated in the shunt resistor.