Gpio Hardware Guideline; Avoid Floating Unused Pin; Cross-Voltage Domains Leakage; Figure 15. Multi Voltage Leakage Example - ST STM32 Application Note

AN4899
6

GPIO hardware guideline

This chapter sums up some of the most important rules to check when developing
applications with STM32 GPIO.
6.1

Avoid floating unused pin

Do not leave unused pin floating. Connect it either to ground or to supply on the PCB, or use
PU / PD. Noise on non-connected input pin is a source of extra consumption by making the
input buffer switch randomly.
If the application is sensitive to ESD, prefer a connection to ground or define the pin as PP
output and drive it to low.
6.2

Cross-voltage domains leakage

In applications with multiple different voltages (for instance 3.3 V and 1.8 V, or 5 V and
3.3 V), check that all the GPIOs with PU are not exposed to an input voltage that exceeds
V . This is particularly valid when optional external circuitry is connected (debugger probe
DD
and systems or others).
Digital
input
ADC
Digital
output
The example provided in
up resistor when the STM32 and the driving buffer are not supplied with the same V
source. The pink arrow marks the leakage current path.

Figure 15. Multi voltage leakage example

Internal V
EnP
GND
Analog
EnN
Internal ground
Figure 15 shows the leakage current induced by the internal pull-
AN4899 Rev 3
DD
PU
ESD
protection
PD
STM32
GPIO hardware guideline
Buffer V
DD
VDD
GPIO
+
DC
leakage
-
GND
PCB
MSv46886V2
DD
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