I have a microcontroller that uses 4 GPIO pins as "bootstrap pins". The state of these pins (high/low) at boot time will determine important features of the microcontroller, such as output voltage to the flash chip.

It is therefore very important that these bootstrap pins have the correct state at boot.

They are defined to have internal pull-up / pull-down by default. The pull-up / pull-down has a strength of 75uA.

Can I safety leave these pins floating and rely on the pull-up / pull-down to set the state at boot? The datasheet seems to suggest that I can. However, I'm worried that stray noise or a finger (or a near by device), might overpower this 75uA drive strength.

Is this a realistic worry? I would like to save the space used by these 4 pointless external pull-up / pull-down resistors that I'm using if possible.

  • \$\begingroup\$ Which microcontroller are you using? \$\endgroup\$ – awjlogan Nov 14 '17 at 16:28
  • \$\begingroup\$ ESP32. Here's the documentation. espressif.com/en/products/hardware/esp32/resources \$\endgroup\$ – Shanee Vanstone Nov 14 '17 at 16:35
  • \$\begingroup\$ It depends a bit on your application. If it's just sitting on your desk, you'll be fine. If you're in a generator hall, you might not be so likely. If you're laying a board out, I would leave space for resistors at least for version one. \$\endgroup\$ – awjlogan Nov 14 '17 at 17:05
  • \$\begingroup\$ If you assume BSP state is unknown before Power is "good" , how can you gaurantee the boot state unless there is a known gauranteed default from POR. 3.3V/75uA=44 kOhm is ok for noise ingress to a small pad. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Nov 14 '17 at 17:18
  • \$\begingroup\$ @TonyStewart.EEsince'75 It's guaranteed at power on. \$\endgroup\$ – awjlogan Nov 14 '17 at 18:01

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