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AMC1304M05: LDOIN / AGND issue

jihong min1
Prodigy 20 points
Part Number: AMC1304M05
Other Parts Discussed in Thread: INA240, AMC3306M25

Dear team:

I designed 2-Phase shunt current measurement circuit with two AMC1304M05 chips.

I have several question in my application.

1. what happened if AGND is not tied to AINN ?

Current sensing application in INA240, for example, Gnd and IN- pins are not tied.

if AMC1304 LDO Supply voltage only used for differential amplifier, that would be no difference between amc1304 with INA240 power supply circuit.

I read a lot of application note about isolated ADC, but I can't understand these circuits are not same.

Is there an issue with connecting VM_5V Power to LDOIN and AGND? VM_5V is regulated from DRV5350RH for other Isolator power, gate logic power supply.

(Mcu power source and DVDD, DGND Pin is not powered from VM_5V, these source is isolated from Motor power)

 Left : AMC1304 Inline Current Sense Applicaiton, Right:  INA240 Inline Current Sense Applicaiton

2. Can AMC3306 replace AMC1304 Applicaiton?

I can't add more isolated power components for each AMC1304 LDOIN Power because I have board size issue.

I think simplest solution is replace AMC1304M05 to AMC3306M25, and reroute pattern.

Can I apply this solution or I supposed to find another way?

Best regards

  • 0
    TI__Guru**** 168745 points

    Hi Jihong,

    Welcome to our e2e forum!

    Regarding your AMC1304M05 question, we recommend tying AINn (or AINp) to AGND so that you stay within the common mode voltage level of the device.  The isolation from input to output (among other things) on the ADS1304M05 is what differentiates it from devices like the INA240.  You can certainly use an LDO to provide a 5V source to the AMC1304, but the internal LDO can accept Vin to 18V.

    With the AMC3306M25, you would not need a high side supply.  Besides the routing and pin-out differences, you can use the AMC3306M25 in place of the AMC1304M05.   You just need to accommodate the higher input voltage range of the part, AMC3306M25 has +/-250mV input range versus +/-50mV input on the AMC1304M05.