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Topic: Sensing resistors of L293E? (Read 839 times) previous topic - next topic

ironbot

Hi,
On L293E there is something called "Sensing Resistors" I can't understand.

I downloaded the datasheet, both L293B and L293E share the same datasheet but while B type is DIP16, E one is DIP20, and on each side of the chip there are two pins for "sensing resistors". I didn't find enough info on the datasheet about the function of them (there is a schematic-application for stepping motor there, but I am to use the chip with spinning dc motors).

I first guessed that I can leave them unconnected and life would go on, but I was wrong: the motors won't move! Next, considering that application note in the datasheet, I just connected each 'sensing-resistor' pin to the ground and life started to go on, but so fast!

While I have pwm from Arduino normally working on my B type chip, after grounding those sensing-resistor pins, the motor spins the fastest way, as if I applied analogWrite(pwmPin, 254) on the 'enable pin' of the chip. Changing the value of pwm applying on the enable pin issues no changes!

I googled for L293E but can't come up with useful info, could anyone please give me some idea how to make the life "controllable" with pwm please? :D

MarkT

They are the returns to ground for each output stage so you can add current sensing resistors per channel - connect to ground if not using current sensing.  There's a chip schematic on the datasheet that shows them.
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ironbot


They are the returns to ground for each output stage so you can add current sensing resistors per channel - connect to ground if not using current sensing.  There's a chip schematic on the datasheet that shows them.


Thank you, but is there any effect on PWMing? I connected 3rd pin of Arduino to en, 2nd and 4th to in1 and in2 of L293B, and I had pwm working ok. When I changed to L293E I setup same pins, connected sensing resistors to ground, but now changing pwm seems having no effect on motor movements! motors are moving always at full speed!

Any idea how to get pwm back, running please?

MarkT

They are just the output stage returns - they are not used on the chip at all, only separated out so you can sense each current independently with external circuitry should you want/need to.
[ I won't respond to messages, use the forum please ]

ironbot


They are just the output stage returns - they are not used on the chip at all, only separated out so you can sense each current independently with external circuitry should you want/need to.


Thank you very much! This cleared question totally! :)

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