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ST92F120R9Q7 bảng dữ liệu(PDF) 9 Page - STMicroelectronics |
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9 / 324 page 9/324 ST92F120 - GENERAL DESCRIPTION 1.2.4.3 Internal Circuitry: Digital I/O pin In Figure 3 a schematic representation of an ST9 pin able to operate either as an input or as an out- put is shown. The circuitry implements a standard input buffer and a push-pull configuration for the output buffer. It is evident that although it is possi- ble to disable the output buffer when the input sec- tion is used, the MOS transistors of the buffer itself can still affect the behaviour of the pin when ex- posed to illegal conditions. In fact, the P-channel transistor of the output buffer implements a direct diode to VDD (P-diffusion of the drain connected to the pin and N-well connected to VDD), while the N- channel of the output buffer implements a diode to VSS (P-substrate connected to VSS and N-diffu- sion of the drain connected to the pin). In parallel to these diodes, dedicated circuitry is implemented to protect the logic from ESD events (MOS, diodes and input series resistor). The most important characteristic of these extra devices is that they must not disturb normal oper- ating modes, while acting during exposure to over limit conditions, avoiding permanent damage to the logic circuitry. All I/O pins can generally be programmed to work also as open-drain outputs, by simply writing in the corresponding register of the I/O Port. The gate of the P-channel of the output buffer is disabled: it is important to highlight that physically the P-channel transistor is still present, so the diode to VDD works. In some applications it can occur that the voltage applied to the pin is higher than the VDD value (supposing the external line is kept high, while the ST9 power supply is turned off): this con- dition will inject current through the diode, risking permanent damages to the device. In any case, programming I/O pins as open-drain can help when several pins in the system are tied to the same point: of course software must pay at- tention to program only one of them as output at any time, to avoid output driver contentions; it is advisable to configure these pins as output open- drain in order to reduce the risk of current conten- tions. Figure 4. Digital Input/Output - True Open Drain Output PIN OUTPUT BUFFER N P N N INPUT BUFFER ESD PROTECTION CIRCUITRY PORT CIRCUITRY I/O CIRCUITRY P EN EN 1 |
Số phần tương tự - ST92F120R9Q7 |
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Mô tả tương tự - ST92F120R9Q7 |
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