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Pin configuration

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RoboWanabe

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I have an IC which i need help configuring.

I am concerned with the two pins DI ( Driver in) and DE (Driver enable)

for both pins it says the Input high voltage must be MIN= VCC-0.4. And Input low voltage max= 0.4v. I belive i must also supply a 20ma current to the pins, this activates a optocoupler diode.

I am driving both pins from a micro whos max pin voltage is 3.3v with a max output current of 20ma.

Can some one please help me with the calculations for a resistor connecting the pins together.

View attachment 68751

I hope i've included everything you need. I do know its simple ohms law whihc i can do but i just struggle biasing a circuit the way i need it, but i've just started a new job and i am learning alot :)
 

geobabu

Member
That depends on the VCC requirement of the IC, that you are using . If its working on 5V, then you need a level convertor here.
If its a 3.3V IC, then you can directly connect the microcontroller's pin that.

Anyway make sure about the IC's operating VCC.
 

dougy83

Well-Known Member
I think you've read it all wrong. What's the part number, or where's the datasheet?
 

dougy83

Well-Known Member
Oh, looks like you did read it right.. excuse me. DE' and DI' are not actually pins but external resistor connection points.

If VCC4 is connected exactly as shown in the block diagram (i.e. it's only connected to the optocoupler anodes), then VCC4 could instead go to 3V3. If as you said, 20mA is the diode current (I didn't see any value), then the diode forward voltage is 1V (20mA * 200ohms). For 3V3 the resistance would become 2V3/0.02A = 115ohms.

If VCC4 cannot be connected in such a manner, then you'd need to use something to drop the voltage (e.g. a few diodes) or a level translator (e.g. a logic IC, or a BJT transistor). Resistance would be the 200 ohms from the datasheet in this case.
 

RoboWanabe

Member
Yea i struggled to see a value for the forward current except the maximum value of 50ma in the "Absolute maximum Ratings" section. the 20ma i worked out by assuming they think ive got a 5v pin output from the micro( because of the xor they put on the input which has an output of 5v?) and dividing it by the recomended reistor of 200ohms? is this not the right way of thinking?. The configuration im using is figure 15 and the type ive got is max1480eacpi :)

Cheers for educating me :)
 
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