LMD18200: Low Output Resistence

Andrew,

Let us clarify what you have first.
"when the part is powered with 28V there was a extra 70mV drop through the circuit along with the chip pulling an extra ~100mA"
a. Assume 28V on Vs pin, is 70mV drop between Vs and Output1?
b. Does Vs pin take ~100mA current? Can you measure Output 1; Output 2 and current sense output voltage? I want to know where does that current go?

I don't know the soft knee issue before. Let us step by step to fix the issue first.
"Apart of our trouble shooting found that the resistance between the switch output and GND is only ~138Ohms. Other switch outputs the we measured was >2MOhms."
When you do this test, what is the Vs pin voltage; PWM pin; brake pin and direction pin voltage?

Assume 28V on Vs pin, is 70mV drop between Vs and Output1? This part drops about 70mV more than other LMD18200 parts that we have tested. You are correct this is when the chip is powered with 28V.
I want to know where does that current go? The current is going thorough the back body diode of the OFF FET within the chip. This part has a ~20C rise compared to other parts we have tested.
When you do this test, what is the Vs pin voltage; PWM pin; brake pin and direction pin voltage? This is with the chip unpowered i.e. open on the Vs pin. We are applying 1V between the switch output pin and GND pin to measure the current to derive a resistance of the back body diode.

Andrew,

1. I still don't know the 70mV voltage between which pin to which pin. You bring another point: it is higher than other parts. What is other part voltage drop?
2. "The current is going thorough the back body diode of the OFF FET within the chip". It is hard to believe the body diode of the FET only has 70mV voltage drop. Is the FET turned on? 100mA with 70mV drop is about 7mW loss. That cannot drive the part 20C rise. So, I would think the 100mA is not in the back body diode of the FET.
3. " This is with the chip unpowered i.e. open on the Vs pin". "We are applying 1V between the switch output pin and GND pin to measure the current to derive a resistance of the back body diode."
Please draw a test block diagram picture to show your measurement. Such as: you add 1V on the part, how do you measure it 70mV?
4. I assume 28V on Vs to discuss the IC power dissipation. But, you said no supply on Vs. So, the IC is off or no control. Your question would be: with IC power off (no Vs supply), why is only ~138Ohms between the switch output and GND on only one part? What values are on other parts? Is that what you want to ask?