What is the pull current, what is the sink current? What is the absorption current?

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What is the pull current, what is the sink current? What is the absorption current?
Pull current and sink current is to measure the circuit output drive ability (Note: Pull, irrigation is the output side, so is the drive capability) parameters, which is generally used in digital circuit.
Here, first of all, the chip manual in the pull, sink current is a parameter value, is the chip in the actual circuit allows the output end pull, sink the upper limit of the current value (maximum allowable). The concept below is the actual value in the circuit.
As the output of digital circuit only high and low (0,1) two level values, high-level output, is generally the output of the load supply current, the value of the supply current is called "Pull current", low-level output, is generally the output to absorb the load of the current, the value of the absorption current is called "pour (in) the current."
For devices with input current:
Both the sink current and the absorption current are input,
The sink current is passive,
The absorption current is active.
If the external current through the chip pin to the chip in the ' inflow ' is called the sink current (is poured into);
Conversely, if the internal current through the chip pin from the chip ' outflow ' is called pull the current (pulled)
2, why can measure the output drive capability
When the logic gate output is low, the current that is poured into the logic gate is called the sink current, the higher the sink current, the higher the output low level. The transistor output characteristic curve also can be seen, the larger the sink current, the greater the saturation pressure drop, the lower the greater.
However, the low level of the logic gate is limited, and it has a maximum value of Uolmax. When the logic gate is working, it is not allowed to exceed this value, and the specification of the TTL logic gate is uolmax≤0.4~0.5v. Therefore, the sink current has an upper limit.
When the logic gate output is high, the current at the logic gate output is flowing out of the logic gate, and this current is called the pull-current. The higher the pull current, the lower the high level on the output side. This is because the output stage transistor has internal resistance, the voltage drop on the internal resistance will cause the output voltage to drop. The greater the pull current, the lower the high level of the output.
However, the high level of the logic gate is limited, and it has a minimum value of uohmin. When the logic gate is working, it is not allowed to exceed this value, and the specification of the TTL logic gate is uohmin≥2.4v. Therefore, the pull current also has an upper limit.
It can be seen that both the pull current and the sink current at the output have an upper limit, otherwise the pull current will make the output level lower than uohmin when the high level output, and the sink current will make the output level higher than uolmax when the low level output. Therefore, the pull current and the sink current reflect the output drive capability. (The larger the number of pull and sink current parameters of the chip means that the chip can take more load, because, for example, the sink current is the load, the more load, the larger the current is poured into)
Because the high-level input current is very small, at the micro-security level, it is generally not necessary to consider, low-level current large, in the mah. Therefore, often low-level sink current does not exceed the problem. The fan-out factor is used to illustrate the ability of the logic gate to drive the same door, and the fan-out factor No is the ratio of the maximum output current at low level and the maximum input current at low level.
In the integrated circuit, the suction current, the pull current output and the sink current output is a very important concept.
Pull-out, active output current, is the output current from the output port.
Filling, passive input current, from the output port into the
The suction is the active suction current, which flows from the input port
The current sink and sink current is from the chip outside the circuit through the pin into the chip in the current, the difference is that the absorption current is active, from the chip input is called absorption current. The sink current is passive, and the incoming current from the output is called sink-in.
Pull current is the output current of the digital circuit output high to the load, the output low level of the sink current is external to the digital circuit input current, they are actually input, output current capability.
The absorption current is for the input (input), while the pull current (output outflow) and the sink current (the output is poured) is relative to the output side.
Give a visual explanation:
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The PB0 output 0,led will light up, the current direction of the PB0 is flow to PB0 is the current, and PB1 to output 1,led will light, PB1 the direction of the current is from the PB1 outflow, that is, pull the current.
In the actual circuit, the sink current is formed by the input low-level current of the logic gate, which is brought together and poured into the output of the front logic gate, readers see figure 18-2-3 self-evident. Obviously its test circuit should be shown in 18-2-4 (b), the input logic level is to ensure that the output can be low level, but the current sink is connected to the power supplyof a potentiometer, the adjustable potentiometer can change the sink current, and the output low voltage value will change.
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(a) sink current load (b) Pull current load
Figure 18-2-3 Sink current and discharge flow
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(a) current-sinking load characteristic curve (b) test circuit
figure 18-2-4 Load characteristic curve and test circuit of sink current
when the voltage value of the output low level increases with the increase of the sink current to the output low level maximum value, namely the Uol=uolmax when the corresponding sink current value is defined as the output low level current quantity large value Iolmax.
different series of logic circuit, the same series of different models of integrated circuits, national standards for the output low-level current maximum value of the Iolmax specification value is often different. The more commonly used values are as follows
TTL series Iolmax=16ma
LSTTL74 Series Iolmax=8ma
LSTTL54 Series Iolmax=4ma
the fan-out factor No is a parameter describing the capacity of the integrated circuit with load, and its definition is as follows 18-2-1)
no= Iolmax/iilmax
where Iolmax is the maximum allowable sink current, the Iilmax is a load gate that is poured into the current level.
the larger the No, the stronger the load capacity of the door. General product regulations require no≥8.
when determining the fan-out factor, it is important to calculate the current value correctly, and for figure 18-2-3, the input end of the logic gate is connected in parallel. When the output is low, the IIl at the back of the logic gate input end is independent of the number of parallel terminals due to the R1 current limiting effect. However, when the output is high, the direction of the current changes to the input end of the flow, the logic gate input stage after the multi-emitter transistor is quite two transistors in parallel. The inflow of Iih is doubled, which is related to the number of parallel end heads. For figure 18-2-3,nol=2, the fan-out factor may be different in the case of noh=3, output low and output high. Since the value of IIL is much larger than that of IIH, the main contradiction in IC is the low-level fan-out factor. So, generally we just need to consider the low-level fan-out factor on it.

What is the pull current, what is the sink current? What is the absorption current?