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ADM1272 EVAL Board at 48V loaded with 5 Ohm

Question asked by Wollli on Nov 27, 2017
Latest reply on Dec 20, 2017 by Wollli

I made some tests with the ADM1272 eval board.

 

I connected a 5Ohm/500Watt load to the outputs of the EVAL board.
(The power supply connected to the eval board is able to deliver currents up to 48V/20A)

 

Initially I wanted to limit the max output current to 10A, so I used a 100k/18k resistor network for R30/R31 (ISET 0,4V).

Then I saw the behaviour shown in the scope image. -> After switching ON the board, the output voltage and current rises up to 16V, then the error LED turned ON and the 48V Output OFF.

 

Ok, I thought may be I miscalculated something removed R31 and replaced R30 with 0R. (Meaning max. 30A output current, This is the original EVAL board state)

 

But the behavior is the same!

 

The output turns OFF after reaching 16,2V. Why ?

 

If I connect the load AFTER switching ON the eval board then there is no fault detected, and the load runs on ~10A,
then there is also no ramp, but this may be ok.

 

Has anyone an idea why?

 

03.12.17
in between I made some more tests, and I saw tht if I use the default ISTART of 25mV (25A)
the outputs turns on without any problems. But I think if I connect bigger capacitors now,
(10000µF) then the FET's will not long stay alive... What's wrong in the design or test setup ?

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