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ADP2441 - VCC goes low when VIN > 8.5V Latch Up

Hi,

I have two ADP2441 regulators on the PCB one at 3.3V (which is working as expected) and one at 5.8V (Schematic included).

When the second regulator is unloaded it behaves normally (reaching regulation at approx VIN= 7V) until VIN > approx 8.5V at this point the internal regulator VCC drops to 1.3V, switching ceases, and the  circuit current draw jumps approx 25 ma. The regulator only recovers if the circuit is power cycled. If there is a load of around 10mA this behaviour does not occur.

So far I have tried replacing the ADP2441, the bypass capacitor and reducing the switching frequency all to no avail.

EN is tied to VIN.

PGOOD is left floating.

I have attached to Scope plots, the first is with VIN = 10V supplied by a bench top power supply and just turning the unit on. The second is slowing increasing VIN until the behaviour occurs.

In both plots all Voltage Div is 5V / Div.

CH1 = ADP2441 VCC pin.

CH2 = ADP2441 Pin 8

CH3 = VIN

CH4 = VOut

I'm really hoping you can help me out, as I'm completely out of ideas.

Thanks

Daniel.

  • Daniel,

    it looks like the internal linear regulator is latching. This can be caused by too much load on the internal regulator. It is possible that the BST cap is the issue. I see you placed a 15nF there, we recommend 10nF. Would you mind trying a 10nF cap on BST?

    It looks like this behavior is happening when Vin is close to Vout. This requires the high side FET to be on almost 100% of the time. I am afraid this then demands too much current to recharge the BST cap at the end of each cycle and if the internal regulator hits current limit while recharging the BST cap it can cause a latch regulator.

    LucaV

  • Daniel,

    I tested your circuit just to confirm my theory about the boost cap value. I was able to show your behavior at no load on our board with 100nF but not at 15nF so there is plenty of margin. Are you sure you do not have 150nF (instead of 15nF) as the BST cap? With an actual load at the output this issue was not re-producible.

    Could you share your layout? I see you have different ground sections (AGND and PGND) how are those connected together? Can you share your layout?

    If you have ground bouncing between AGND and PGND I ca see how this could be an issue.

    LucaV

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