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proper charging and discharging of dc-dc using mosfet

Hello,tc1261lcs8 needs to be both turn on and off using esp8266 3.3V GPIO pulse and the output needs to charged and discharged with this GPIO pulse.When my GPIO =0V output off when GPIO=3.3V output is ON.
Which is the opposote of what the SHDN does as shown in the data sheet below.I have made an inverter as shown below .
I want to discharge the negative voltage to ground using NMOS.
Vg=5V and Vs=-2V so the NMOS is open.

However the output only goes from 0 to -1 instead of 0 to -2.4 expected by the formula below as it was withoud the SHDN switching.
Why its not charging back to -2.4V?
another problem is that i want the output to be discharge at logical 1 (5V) but here i got the opposite)
Is there something that could be done?
Ltspice model is attached.


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M3 become conduct when source are negative. Try to connect M1 source to net out_DC_DC? May be with series resistor (tenth kOhms) between net Vout_inv and SHDN pin.

Or use for discharge P-JFET.

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Hello, tofik80,given the data sheet how do you know the proper conditions for the input  current and voltage?

Also is there a way to speedup the charging? with mosfet i got a much higher charging rate.


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The charging speed is determined by the operating algorithm U2. The charging speed can be increased by decreasing the value of c3, but this will increase the output ripple.

Edited by tofik80

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