LPC55S69 : 6.1.1 Termination of unused pins

[EugeneHiihtaja]

Hello !

In DS I can see the next recommendations:

"

Unused pins with GPIO function should be configured as outputs set to LOW with their
internal pull-up disabled. To configure a GPIO pin as output and drive it LOW, select the
GPIO function in the IOCON register, select output in the GPIO DIR register, and write a 0
to the GPIO PORT register for that pin. Disable the pull-up in the pin’s IOCON register.
In addition, it is recommended to configure all GPIO pins that are not bonded out on
smaller packages as outputs driven LOW with their internal pull-up disabled.

"

But MCU loze DIR registers in PowerDown mode and all outputs start to be inputs.

Should be enable PullDown resistor for unused pins if if use PowerDown Low power mode ?

Or what kind of recommendations can be given for minimize effect of PowerDown mode for nonused GPIO pins ?

Regards,

Eugene

[xiangjun_rong]

Hi, Eugene,

As you know that during power-down mode, all the GPIO pins become input mode, so this is my opinion, I suggest you connect an external pull-down resistor on the unused pins. In active mode, you do not need to configure the unused pins as GPIO and output LOW logic, you do not need do any initialization, just keep it's default input mode for the pin, it is okay. From my experience, all unused pins have to keep a fixed logic(0 or 1), but float is not recommended, which leads to high leakage current.

BR

XiangJun Rong

[EugeneHiihtaja]

Hi xiangjun.rong‌ !

Can we use repeater mode for configure unused GPIO pins ?

In this case in Powerdown mode, PD resistor will be active.

Or external resistor is much better ? But it is difficult to route those everywhere.

Regards,

Eugene

[xiangjun_rong]

Hi, Eugene,

As you know that the GPIO pin will be in input mode in default if you do not initialize the pin, if the input pin does not connect a pull-up or pull-down resistor, the pin will be float, the float pin are NOT expected, the middle-voltage for the input pin is also not allowed. So in order to save power, every input pin must has a fixed logic low or high. So I think repeater mode is okay, because the pin will be LOW or HIGH, it can not be float or middle-voltage in repeater mode.

Hope it can help you

BR

Xiangjun Rong