Output Type

Usually the product would have two different types of output: Push-Pull and Open-Drain.

In this case, we are using the chip from Microchip. MIC7211/MIC7221.

Be careful that 7211 is push-pull output and 7221 is open-drain output. Therefore, if we use MIC7221, we need a pull-up resistor to the power supply. Otherwise there will NOT be any output (always 0).

Meanwhile, when choosing pull-up resistor, we have to find the proper “Supply Current” in the datasheet, which is 7 uA under 5V Vdd. Therefore, the resistor should be about 700 kOhm.

  • Phenomenon of over supply current
    If the resistor is too small, (say 10kOhm), therefore will be over-supply-current. Then the MOSFET will be turned on forever, it won’t change with the input until you shut the power and restart the board.