VALID Input Detection
Measuring the power supply input and the VALID output of the LTC4417, we get the following graph:
We see the appropriate ~256mS delay between the input being good and it being declared valid.
Switchover between valid inputs:
2 inputs were connected to the device within the valid range. The solid cursor shows when the power source was turned off. The output voltage (DARK BLUE) can be seen falling, and once it reaches the UV level, then the VALID output for that channel (PURPLE) immediately goes high (8uS delay according to datasheet). Then the alternate source is switched in and the voltage stays stable. The second input was a second power supply set to 13V.
YELLOW = 12.5V input voltage (stayed on)
DARK BLUE = Output Voltage (can be seen falling from 13-12.5V)
LIGHT BLUE = VALID for 12.5V PSU
PURPLE = VALID for 13V PSU.
The total switchover time was 4.2mS. This test was done with no load on the output. We will try this again with a load on the output.
Switchover with Load - Reset Loop Mode
At this point, the board start to go into the restart loop mode, so let’s go in to that a bit. This is with a 0.5A load on the output of the board.
Here is a graph of what is happening during the reset loops. This is with a single power supply connected to the DC-DC input.
YELLOW = Input voltage
DARK BLUE = Output voltage
LIGHT BLUE = AUX Valid (Aux was never turned on)
PURPLE = DC-DC Valid
Without a load on the output, the voltage decays much more slowly.
If we turn on a second input with a lower priority also at the edge of its voltage range, then the board behaves similarly, except this time with both inputs switching between valid and invalid:
