Hello All,
I'm trying to make an ICL7665 based low voltage cutoff board work.
Here is the datasheet: https://datasheets.maximintegrated.com/en/ds/ICL7665.pdf
I'm using it to prevent undervoltage discharge on 18V lithium ion battery packs (20V fully charged). I want it to cut the load supply at 15V (3V per cell) and have about 1-2v hysteresis.
I'm using an IRFZ44N mosfet as the power transistor: https://www.infineon.com/dgdl/irfz44npbf.pdf?fileId=5546d462533600a40153563b3a9f220d
I'm using an LP2950 (3V fixed) for the LDO regulator (since the max voltage for the ICL7665 is 16V).
https://www.onsemi.com/pdf/datasheet/lp2950-d.pdf
I have potentiometers on the SET and HYST pins to "tune" the voltage manually as I couldn't make sense of the formulas in the datasheet. The resistor values on the schematic make the MOSFET turn off at 15V and turn back on at about 16.5V (hysteresis). I found these with trial and error.
The whole system is currently using about 0.6mA which is very high. The ICL7665 only uses 3uA, so the rest must be the LP2950 and resistors.
Here is my circuit:
Here are the problems I am having:
Thanks in advance for any help.
I'm trying to make an ICL7665 based low voltage cutoff board work.
Here is the datasheet: https://datasheets.maximintegrated.com/en/ds/ICL7665.pdf
I'm using it to prevent undervoltage discharge on 18V lithium ion battery packs (20V fully charged). I want it to cut the load supply at 15V (3V per cell) and have about 1-2v hysteresis.
I'm using an IRFZ44N mosfet as the power transistor: https://www.infineon.com/dgdl/irfz44npbf.pdf?fileId=5546d462533600a40153563b3a9f220d
I'm using an LP2950 (3V fixed) for the LDO regulator (since the max voltage for the ICL7665 is 16V).
https://www.onsemi.com/pdf/datasheet/lp2950-d.pdf
I have potentiometers on the SET and HYST pins to "tune" the voltage manually as I couldn't make sense of the formulas in the datasheet. The resistor values on the schematic make the MOSFET turn off at 15V and turn back on at about 16.5V (hysteresis). I found these with trial and error.
The whole system is currently using about 0.6mA which is very high. The ICL7665 only uses 3uA, so the rest must be the LP2950 and resistors.
Here is my circuit:
Here are the problems I am having:
- Output voltage from the regulator is being pushed to 18V when the input voltage is 20V. If I remove the ICL7665, the regulator output drops to 3.0V. I suspect voltage from the HYST pin (18V is present here) is being fed internally to the Vin. I don't know why.
- Gate voltage of MOSFET is very low (0.6V) when the system is in normal operation (battery voltage above 15V). Is R3 resistance too high?
- High current use of the system.
Thanks in advance for any help.