Active-Low enable input driven by high voltage signal

Thread Starter

mspider65

Joined Sep 20, 2021
3
I'm an hobbist, and due to the chip shortage I am trying to adapt the circuit of my Open Source project TSDZ2 Bluetooth interface to use what is available.
In particular, I have to replace a Step-Down which, starting from the voltage of an e-bike battery, should generate 5V.
The doubt concerns the Enable signal of the new DC-DC which is now active low.
What I have is an output (PSU_ON) which in case of ON is at battery voltage while in case of OFF it is at GND or floating.
The EN input must be less than 0,8V to enable the chip and must be above 1,8V to disable the chip.
Max Voltage at enable pin is 7V.
I thought of using the circuit you see below but I ask those who have more experience than me for an opinion if it can be good or if there is a better way to go.
In particular i have a very small footprint to accommodate everything and any suggestion to lower the number of needed component is welcome.

circuit.png
 

Juhahoo

Joined Jun 3, 2019
253
Looks good to me. If your ENABLE could swing only between 0V(gnd) and Vin, you could replace R2, R3 Q1 with diode, but since floating also means OFF, it is not possible.
 
Last edited:

Thread Starter

mspider65

Joined Sep 20, 2021
3
Looks good to me. If your ENABLE could swing only between 0V(gnd) and Vin, you could replace R2, R3 Q1 with diode, but since floating also means ON, it is not possible.
Thanks,
i plan to replace R4 with a zener diode in order to clamp EN input voltage regardless of VIN battery voltage.
I have another question, how much could be R1 value increased in order to reduce the battery leakage current when the battery is left connected ?
 
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