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4-channel
5V Vcc
Level shift PWM signal voltage from 3.3V to 5V https://docs.holybro.com/autopilot/pixhawk-baseboards/pixhawk-baseboard-ports
Selected SN74AHCT125PWR SN74AHCT126PWR for cheap price and small package.
3.3V buffer backup: SN74HC125PWR
5V LDO
Current consumption of the buffer is 25mA max, Vdrop = 6V- 5V = 1V, Ploss = 25mW worst case. No need for a big package to dissipate heat. Selected TLV76050DBZR for cheap price and small package.
3.3V LDO backup: TLV76033DBZR
Input Pulldown Resistors
I couldn’t find Pixhawk PWM rail leakage current. Assuming 100uA leakage current from Pixhawk, 4.7k pulldown will create a 0.47V input, which is below the 0.8V logic low threshold.
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