What are the features and use note of CMOS circuit?
( 1 ) Features
1 ) Low static power consumption. The static power consumption of the medium-scale circuit Vpp = 5V is less than 100W, which helps to improve the integration and packaging density, and reduce the cost, reduce power consumption.
2 ) Wide range of supply voltage. The power supply voltage can be selected in the range of 3 to 18 V, which makes the choice of power supply great, and the power supply design requirements are low.
3 )High impedance. The normal working CMOS circuit, the input protection diode is in the anti-bias state, the DC input impedance can be greater than 100MΩ, when the operating frequency is high, consideration should be given to the impact of losing capacitance.
4 ) Strong fan-out ability. In low frequency operation, an output can drive more than 50 CMOS devices, mainly because of the high input resistance of CMOS devices.
5 ) Strong anti-jamming capability. The voltage noise tolerance of CMOS circuits can reach 45 % of the supply voltage, and the noise tolerance limits of high level and low level are basically equal.
6 ) Large logical swing. When empty, the output high level VoH > ( VpD-0.05V ), the output low level VoL < ( Vss + 0.05 V ).
A protective diode is connected between the input end of the CMOS device and Vss. Besides some interface circuits, such as the level converter, there is also a guarantee between the input terminal and the positive supply Vo protecting diodes, therefore, in normal operation and welding CMOS devices, generally will not damage the device due to induced charge. However, when using CMOS circuits, the low level of the input signal cannot be lower than ( Vss-0.5V ), except for some interface circuits, the high level of the input signal shall not be higher than ( VDD + 0.5V ), otherwise it may cause the protection diode to turn on, even damage, which may cause damage to the input stage.
( 2 ) Use Note
1 ) Power connection and selection.
Vpp is connected to the positive pole of the power supply, and the VSS terminal is connected to the negative pole of the power supply. Absolutely not allowed to take the wrong, otherwise the device is damaged due to excessive current. The output impedance, working speed and power consumption of CMOS devices are changed at different supply voltages, which should be considered in the design.
2 ) Handling.
The excess input can not be left vacant. It is logical that the VoD or VSS should be connected to the VoD or VSS, otherwise,that can cause logical confusion and even damage the device. For the work speed requirement is not high, and the requirement to increase the load capacity, can be connected together to use the input. For CMOS devices installed on the printed circuit board, in order to avoid the suspension of the input terminal, the current limiting resistor and the protection resistor should be connected to the input terminal of the circuit board, when V = + 5V, the current limiting resistor is 5 k ohm, the protective resistance is generally 100 k ohm-1 Megohm.
3 ) Output processing. The output end is not allowed to directly connect Vpp or VSS, otherwise the device will be damaged. In addition to the tri-state ( TS ) device, two different chip outputs are not allowed to be used in parallel, but sometimes in order to increase the driving capability, the same signal output on the same chip can be connected in parallel.
4 ) Requirements for the signal U of the input. U's high level U1H < VDD, U low level U is less than the low voltage allowed by the circuit system, not less than VSSO
5 ). You must turn on the power, and then add the signal. After work, you should remove the signal, and then turn off the power. You can not plug in or pull out the component when the power is turned on. Welding and storage requirements. The grounding of the electric iron should be reliable, or the electric soldering iron can be quickly welded with the waste heat after the power is cut off. During storage, the components are generally short-circuited with metal foil or conductive foam.
This article is from Allicdata Electronics Limited.