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I am trying to control (Turn ON/OFF) a Voltage Regulator which has an enable pin by connecting it to a digital pin of a micro-controller. I need help to find the resistor values (R1 and R2) to be used for the interfacing. Please find my circuit below.

schematic

simulate this circuit – Schematic created using CircuitLab

Specifications

The microcontroller works on 3.3V and the GPIO1 current is limited to 4mA. The Voltage Regulator enable pin logic high minimum is 2.4V, logic low maximum is 0.8V and the max current is 750uA LDO

Datasheet - https://www.mouser.in/datasheet/2/268/MIC2915x_30x_50x_75x_High_Current_Low_Dropout_Regu-1889172.pdf

I am beginner and would appreciate any help to understand other challenges for this interfacing.

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1 Answer 1

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R1 can be omitted if the GPIO of the MCU is configured as a push-pull output. The regulator allows a direct connection from MCU's GPIO pin to EN input but still a 1k resistor (R2) is sufficient.

Note that the regulator will not be enabled without MCU's enable signal. If MCU fails for some reason then the regulator will output zero.

R1's value is not that important as it prevents the regulator to run if the MCU fails or is not placed during production. It can be pulled up to +3V3 if the regulator should run without the need of an MCU (Thanks to @Transistor for pointing out).

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  • \$\begingroup\$ OP could add a pull-up or pull-down resistor to have a defined default mode if the MCU fails and the output is tri-stated. \$\endgroup\$
    – Transistor
    Aug 23, 2020 at 8:51
  • \$\begingroup\$ @Transistor yes, you are right. \$\endgroup\$ Aug 23, 2020 at 8:53
  • \$\begingroup\$ Thanks for pointing that out. The default mode for LDO must be power OFF. Hope I can proceed safely with R1 - 10K and R2 - 1K \$\endgroup\$
    – Zac
    Aug 23, 2020 at 9:17
  • \$\begingroup\$ @Zac, what is R2 doing for you? I don't see any benefit. \$\endgroup\$
    – Transistor
    Aug 23, 2020 at 12:02
  • \$\begingroup\$ @Transistor I guess R2 will limit the current flow in case of some shorting in LDO, thus saving the microcontroller. 1K would limit the current to less than 4mA. Are there any downsides in using R2? \$\endgroup\$
    – Zac
    Aug 24, 2020 at 12:30

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