Other Parts Discussed in Thread: LM5164, AMC1301
The schematic represents an Isolation Monitoring Device(IMD) for a HV System specifically for EV Application.
The Voltage rating of the Battery Pack is 400V when fully charged.
The schematic consists of 3 blocks:-
1) Isolation Leakage Current Measurement.
2) High Voltage Measurement.
3) Power Supply.
4) Communication.
I would like to share the schematic in private.
1) Isolation Leakage Current Measurement:-
As per the standard Isolation resistance rating of 500 ohm/volt, the resistor value is set on both HV-POS and HV- NEG Lines.
We are utilising Opto - Mosfets category of Solid State Relays for cost effectiveness instead of the Solid state relays used in the TI reference design document.
The Opamp non-inverting pin is referenced through a 2.5V Vref IC.
Both the Opto- Mosfets and the Opamp is referenced to Chassis ground.
2) High Voltage Measurement:-
The voltage divider circuit is designed such that it can measure upto 410V and create a voltage difference across R29 of 250mV.
The differential input Opamp is used to give a single ended output to the MCU ADC in the range of 0 - 4.1V.
3) Power Supply:-
An external 24VDC referenced to chassis ground is given to LM5164 whose output 5V is given to all the peripherals except for the Vdd2 of Digital Isolator SI8652 which is supply by an external 5V supply referenced to MCU ground.
And the AMC1301 is supplied by another isolated Power Supply on the HV side and the chassis referenced supply on the LV side.
4) Communication:
The 5 channel digital isolator is used for communication isolation between the MCU and IMD side which is referenced to chassis.
The Resistors used on the HV side for Isolation leakage current measurement and High Voltage Measurement are MELF resistors of 1% tolerance.
We would like to know if the Circuit is correct interms of different ground references for the IMD function to happen properly.
Also the TI document referred for designing this is the TIDUDJ6B.
Would like to have your valuable feedback on the same.
Thanks
Regards
Mohammed Ibrahim Saqib
