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We are using the AP63356Q to step down voltage from 12V to 5V. During test we can see that the circuit constantly draws around 9mA current, with no load on the IC. We have the exact same configuration as in the datasheet here: enter image description here

But without the C4 and C6 capacitors. The regulator is always enabled as the enable pin is tied to Vin. Reading from the datasheet the Quiescent Supply Current of the IC should be 258uA, so quite far from we measure.

What is the reason for the power draw in this system?

Thanks.

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The specification of current consumption is when the device is not actively driving its internal MOSFETs. If you look closely at this: -

enter image description here

You can see that VFB is forced to 1 volt and, this is higher than the 0.8 volts seen on that pin when actively regulating the output: -

enter image description here

Hence, there is no switching of the internal MOSFETs and, the device will show a low current consumption.

The 9 mA you are reading is when the device is operating and regulating the output.

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  • \$\begingroup\$ So what you are saying is that the IC will consume 9mA on its own? It seems quite high. Can you see this value somewhere in that datasheet as its important to know the "no-load-but-active" current consumption. \$\endgroup\$
    – stackman82
    Oct 27, 2022 at 11:45
  • \$\begingroup\$ I'm just pointing out to you the true meaning of the 285 uA @stackman82 I'm not saying it will consume 9 mA on its own because to decide that I'd need to perform a simulation and read the data sheet for an hour or so. \$\endgroup\$
    – Andy aka
    Oct 27, 2022 at 11:48
  • \$\begingroup\$ I get that and I understand that I'm not measuring it in Quiescent state, but in active. But I just think its strange that it consumes 9mA in active state. \$\endgroup\$
    – stackman82
    Oct 27, 2022 at 11:50
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    \$\begingroup\$ It makes complete sense; look at figure 2 in the data sheet. At low load current (say 2mA) the efficiency is about 5%. Therefore, load power is 5 volts x 2mA = 10 mW and input power is load power / 5% = 200 mW. Minus the output power of 10 mW and you have a wasted power (190 mW). If the supply is 12 volts then the quiescent supply current will be about 16 mA. I expect that if the graph extended a little more to the left we could get down towards a 9 mA consumption so, it seems like 9 mA is about right. \$\endgroup\$
    – Andy aka
    Oct 27, 2022 at 12:00

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