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What is the use of IC 74ACT244MTCX (dsPICDEM MCLV-2 development board)

electronicsLearner77

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upload_2020-11-23_0-42-58.png

I have seen IC 74ACT244MTCX as a part of motor control circuit. I downloaded the data sheet and found as Line driver and when try to understand, i only see lot of tables and it is difficult grasp information. What is this IC, why do i need to use this?
 

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bertus

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Hello,

There are 2 X 4 line drivers (buffers) in the chip.
When you look at this drawing, it might become more clear:

74XX244_logic.png
The /OE input can disable the 4 connected ports, making the outputs high-Z.

You might want to download the LOGIC Pocket Data Book:
https://www.ti.com/lit/ug/scyd013b/scyd013b.pdf

Bertus
 

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electronicsLearner77

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I checked the circuit the following are the observations
Pin 1 and Pin 19 are grounded and as per the data sheet and the truth table
upload_2020-11-23_17-30-6.png
The outputs do not go to high impedance state.
If the input is H/L the output is H/L.
upload_2020-11-23_17-58-32.png
So, the main purpose of the IC is it will convert the 3.3V PWM signal to 5V signal. Am I correct? This is called amplification? Does it increase current also?
 

bertus

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Hello,

I do not know what the MCU can deliver.
The ACT can deliver 24 mA max. (see the attached datasheet in post #2)

Bertus
 

electronicsLearner77

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Thank you very much for the support, I looked up to the datasheet and it is 24mA. So, i assume that the current levels are increasing from Micro to after the line driver (I confirm what the MCU deliver). One basic question i want to understand is, let us say the ACT is able to deliver 24mA, the IC to which it is connected let us say X1 and has got some resistance R1, the resistance R1 should be in the range such that it (X1) should not draw more than 24mA or should be less than 24mA, else the circuit will fail (or we cannot predict the behavior). Is my understanding correct? Please advise.
 

bertus

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Hello,

What will the ACT be driving?
Without the rest of the schematic, we can only be guessing.

Bertus
 

bertus

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Hello,

I see that the ACT is driving some gate drivers, wich are just logic inputs and will not draw many current:
electronics learner 77 driver sch.png

bertus
 

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electronicsLearner77

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Hello,
will not draw many current:
bertus
How did u arrive at this conclusion? Can you please tell me? Suppose if i design my circuit, what is the parameter i have to look for in the data sheet to find out how much current it draws? In the present data sheet of IR2181, which parameter i have to look for to find out the current it draws? Will it be same under all conditions?
 

Harald Kapp

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per ohm's law if the voltage increases obviously the current should increase. Am i correct?
That is valid for resistive loads only. Semiconductors are not resistive loads.
Another point: this has nothing to do with the capability of a driver to supply current.

Yes it does provide more current.
Sorry Constantin, but this cannot be said definitely. One needs to know the properties of the source of the driving signals (e.g. PWM1H1) to answer this question.
You are probably right, but is based on guessing :rolleyes:.
 

electronicsLearner77

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Another point: this has nothing to do with the capability of a driver to supply current.
From above point i assume the ACT is only for level shifting and we are not concerned of the current rating of the ACT, if it can provide minimum current should be fine?
 

Harald Kapp

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There are IR2181 MOSFET drivers that require max. 60 µA input current (datasheet). That is next to nothing with respect to a 74ACT244's max. output current. All is good.
 

electronicsLearner77

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upload_2021-1-18_20-17-34.png
upload_2021-1-18_20-18-31.png

I have few questions on the currents flowing in the schematic.
1. In the top highlighted red item, what is the purpose of the resistor R32?
2. In the next highlighted red item, what is -DC? Gnd and -DC are shorted, i don't understand that terminology.
3. I don't understand SHUNT_LOW_SUM it is passing through resistor R12, i can only see a voltage drop happening? But current should not change. He is generating a Fault signal by comparing both of them. How is it possible? Please help.
 

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