For a battery powered ultra low consumption application I designed a classical high side switch using the complementary MOSFET FDMA1032CZ. this is the schematic:
The idea is simple:
- before shipping, the circuit consumption is nearly 0[A] (only MOSFET and battery leaks),
- then the user powers on the circuit using switch S1,
- the microcontroller starts running and activates Q1-N and Q1-P via "PWR_ON" signal,
- the circuit is then continuously powered on by the battery through the mosfet switch.
I need assistance to calculate the optimal value for both pull-up and pull-down resistors (R1 and R2). For reminder, those 2 resistors are mandatory to set voltage level when circuit is powered on.
In my opinion those resistors must be :
- as large as possible to minimize current when the 2 mosfets are on,
- but not too big to make sure the 2 mosfets can switch fully on.
When looking at datasheet, it appears that the maximum MOSFET gate body leakage IGSS_max = +/-10[uA] and the minimum gate threshold voltage VGSth_min = +/-0.6[V].
According to previous point 2), the resistor value should NOT be greater than R_max = VGSth_min/IGSS_max = 0.6/10e-6 = 60[kohm].
For a battery voltage of 3V, this would result in a total consumption through the resistors of: I = 2x V_BAT/R = 2x 3/60e3 = 100[uA], which is far too big...
I would appreciate if someone could confirm and/or correct my calculation.