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ACT4088 Quiescent Current

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active-semi asked 9 months ago
Good day, I have just completed prototype run of 50 units using ACT4088. Shottky is SS26, cap is 22u ceramic (X5R), 4.7uH inductor, 49.9K resitor feedback, with 10K to ground, delivering correct level of 4.8V. Using 22n boost capacitor. Current delivery is correct, and loading with 1.5A is good. I have the enable unconnected, so always on. Supply voltage 12- 20V. All looks good, however the quiescent current is 17mA. Spec sheet suggests 2mA max. The En measure 6.3V while floating, the fb pin is 0.8V. Ripple looks good. What am I missing on Iq? Many Thanks. Hugh
1 Answers
Michael Day answered 9 months ago

I think there might be some confusion about the difference between “supply current in operation”, “quiescent current” and “no load current”. “Quiescent” and “supply current in operation” are the same thing in this datasheet. It is defined as the current required to power the IC. This current is specified without switching. It might not be obvious, but the test condition of Vfb=1V is what forces the IC to not switch for this test. Because Vfb is > 0.8V, the IC does not switch.
It looks like you measured the “no load current”. This includes the quiescent current, plus other currents caused by switching losses. Even with no load, you have gate drive losses, switching losses, etc.