I am testing this circuit on a PCB that I've built and I'm experiencing a 1 mA current draw when enabling it. The aim is to turn on/off a transceiver that needs 3 V and max current draw of around 500 mA. TCVR_PWR is controlled from an MCU with voltage domain being 3 V as well. I'm suspecting that I made an error in my component selection (NPN or the P-channel) but I'd like a second opinion because I can't identify any issues so far.

TCVR is currently in sleep mode due to AT Commands sent, and draws 4 nA when in said power mode. I can test the difference by shorting 3V0 and 3V0TCVR through a 0 Ω resistor (not pictured in the schematic), which is how I noted the 1 mA current difference.

P-Channel MOSFET Switch


1 Answer 1


and I'm experiencing a 1mA current draw when enabling it.

It's normal.

The base resistor of Q5 digital transistor is 4k7. So when the TCVR_PWR is 3V the base current will be somewhere around 0.5mA:

$$ \mathrm{I_B=\frac{3V-0.6V}{4.7 \ k\Omega}\approx 0.5 \ mA} $$

When the Q5 turns on the 3V rail will be loaded with R11, 10k. Another 0.3mA comes from there:

$$ \mathrm{I_X=\frac{3V}{10 \ k\Omega}= 0.3 \ mA} $$

This makes 0.8 mA total.

To decrease it, you can increase R11 as much as possible (even 500k should work), and replace Q5 with a logic-level-gate NMOS such as 2N7000 or 2N7002. This will decrease the extra consumption to uA range.


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