General purpose input/output, more commonly known as GPIO, is a digital signal pin that can either be configured as an input or output on an integrated circuit. GPIO is a standard interface for a microcontroller to communicate. If GPIO pins are exposed to the outside world, then there is a risk of an electrostatic discharge (ESD) event. The addition of an ESD protection diode is recommended to protect the system against harmful transients. To verify the system is protected properly from any damaging ESD strikes, the characteristics of the GPIO interface must be considered for correct ESD diode selection.
GPIO pins are common across various systems and applications, and can be used to read values from sensors, control LEDs, and read the state of switches. GPIOs have a low voltage of 3.3 or 5V and require a low voltage ESD protection diode. Depending on the number of GPIO pins that must be protected in the system, a single or multichannel diode can be used.
There are many sources of ESD including sliding a plastic container across carpet or removing shrink film from a PCB. This charge can build up and eventually discharge on an exposed connector that is present, including a GPIO header or human interface port. When a connector is in contact with the outside world, the system is at risk of a high voltage strike. This ESD strike or transient event can cause damage to the downstream components in the system.
To protect GPIOs, follow the list of parameters:
Table 1 lists device that support these specifications.
The first step in selecting an ESD diode is the system requirements. For this example, the system is a 3.6V microcontroller with an absolute maximum voltage of 6V, only positive voltages, and eight GPIO pins that require protection. Based on the system requirements, the working voltage of the diode can be 3.6V. Since only positive voltages are seen on the line, a unidirectional diode is recommended. An absolute maximum voltage of 6V causes the diode to have a clamping voltage less than six. With eight GPIO pins needing protection, a multichannel device is recommended but eight single channel devices can also meet the requirements. An example is shown below using ESDS304 as the protection diode that meets the above requirements.
ESDS304 was selected for protection because the device met the system requirements. When selecting an ESD diode for GPIO or any application, considering the system requirements is required to properly protect the circuitry.
GPIO pins require ESD protection to survive real-world ESD strikes. Selecting the correct protection diode is crucial in maintaining system functionality and coverage in the event of a high voltage transient. Table 1 lists device recommendations for protecting GPIO pins, and more devices can be found here.
Device | VRWM (V) | IEC 61000-4-2 (kV) (Contact/Air-gap) | Channel Count | Polarity | Package Size (mm) |
---|---|---|---|---|---|
ESD351 | 3.6 | 30/30 | 1 | Unidirectional | DFN1006 (1.00 × 0.60) |
ESDS304 | 3.6 | 30/30 | 4 | Unidirectional | SOT-23 (2.90 × 2.80) |
TPD8E003 | 5.5 | 12/15 | 8 | Unidirectional | WSON(1.60 × 1.35) |
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