I've just finished a small circuit that uses a PIC16LF1823 to switch on and control a WiFi module using a high-side NX2301 pFet. The circuit is powered by an XC6215B332MR-G, which is a linear 3.3V regulator that has a nominal 200 mA current capacity. The entire circuit, when powered up, consumes around 130 mA. That's well within the regulator's capabilities, and in fact, it works beautifully.
I'm quite content with the entire setup, because it's battery powered (4xAAA) and it draws only about 14 µA (without C1) from the pack when the WiFi module is switched off. The WiFi module is intended to be used only once a month, and that for only less than a minute. So the battery pack should be able to last quite a few years before it needs to be replaced.
The problem is that, if I weren't to place a 470 µF electrolytic capacitor (C1) as shown above, the MCU would reset itself due to the sudden power draw demanded by the WiFi module whenever I switch M1 on. With C1 everything works flawlessly... and without it all hell breaks loose...
Here's the thing: I HATE THAT CAPACITOR ...
Why my intensely negative animosity towards said innocuous and innocent component?... a fair question... There are mainly two reasons:
Although the latter reason is the most significant, the former is a PITA just as well.
It's as simple as this, the leakage current of said capacitor subtracts several years of blissful operation from my precious battery pack.
I have tried applying PWM to the pFet's gate so as to gradually ramp up the power to the circuit to no avail. Even if I were to switch the MCU_pin low (remember, it's a pFet, so MCU_pin is high when the transistor is off) for one microsecond every 0.00017 seconds (that's a 0.2% duty cycle) the regulator would be overloaded and the MCU would reset itself.
Here's my question:
In the event that keeping the odious capacitor becomes unavoidable, is there an easy technique that would allow to gradually charge the capacitor, and then switch the entire circuit on, but without using another of the MCU's I/O pins? ... and then afterward to disconnect both the WiFi module and the cap so as to go back to the ultra-low power draw operating mode?
I'm quite content with the entire setup, because it's battery powered (4xAAA) and it draws only about 14 µA (without C1) from the pack when the WiFi module is switched off. The WiFi module is intended to be used only once a month, and that for only less than a minute. So the battery pack should be able to last quite a few years before it needs to be replaced.
The problem is that, if I weren't to place a 470 µF electrolytic capacitor (C1) as shown above, the MCU would reset itself due to the sudden power draw demanded by the WiFi module whenever I switch M1 on. With C1 everything works flawlessly... and without it all hell breaks loose...
Here's the thing: I HATE THAT CAPACITOR ...
Why my intensely negative animosity towards said innocuous and innocent component?... a fair question... There are mainly two reasons:
- It's big, bulky and ugly.
- It draws an unacceptable amount of waisted current due to its inherent internal resistance.
Although the latter reason is the most significant, the former is a PITA just as well.
It's as simple as this, the leakage current of said capacitor subtracts several years of blissful operation from my precious battery pack.
I have tried applying PWM to the pFet's gate so as to gradually ramp up the power to the circuit to no avail. Even if I were to switch the MCU_pin low (remember, it's a pFet, so MCU_pin is high when the transistor is off) for one microsecond every 0.00017 seconds (that's a 0.2% duty cycle) the regulator would be overloaded and the MCU would reset itself.
Here's my question:
In the event that keeping the odious capacitor becomes unavoidable, is there an easy technique that would allow to gradually charge the capacitor, and then switch the entire circuit on, but without using another of the MCU's I/O pins? ... and then afterward to disconnect both the WiFi module and the cap so as to go back to the ultra-low power draw operating mode?
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