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Author Topic: Help Using a Full Bridge Motor Driver  (Read 779 times)

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Offline Warhawk87Topic starter

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Help Using a Full Bridge Motor Driver
« on: May 07, 2012, 07:24:24 PM »
Hey guys,

After a series of bad component choices, I am left with two overpowered motors (http://www.pololu.com/catalog/product/1102/specs) and 4 L6202 Full Bridge Drivers (http://users.ece.utexas.edu/~valvano/Datasheets/L6203.pdf) for them which I am having trouble with.

My first issue is that I dont have capacitors for the BOOT1 and BOOT2 pins shown on the datasheet.  I hoped I could just tie the pins to ground without too much trouble, please let me now if that thought is stupid.

Secondly, I have a 10k ohm resistor connect SENSE to GND, please let me know if this is correct because I didn't really know what I was doing when I put that together.

Third, with Enable tied to +5 Volts and Source to +12 Volts, the outputs produce +10 Volts no matter the combination of +5 or 0 volts given to IN1 and IN2, with the exception of IN1 High and IN2 Low, with makes OUT2 close to zero but OUT1 remains +10 Volts. 

To summarize, my problem is this.  I cannot get my L6202 to produce +12 Volts to OUT1 when IN1 is at +5 Volts nor produce +12 Volts to OUT2 when IN2 is at +5 Volts.  Therefore, I cannot run my motors correctly.  I am a novice, and I don't know too much about electronics, so any help is greatly appreciated.  Thank you for your time and help!

Also, I'll try to post a rough schematic of what I have hooked up.

Offline Warhawk87Topic starter

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Re: Help Using a Full Bridge Motor Driver
« Reply #1 on: May 07, 2012, 08:03:31 PM »
Here is the ROUGH Schematic, I believe that with this configuration I believe Output 2 should be 12 volts where Output 1 is 0V, but that isnt the result I get.

I forgot to add pin 7, which isnt connected anyway so it is of no importance
« Last Edit: May 07, 2012, 08:05:07 PM by Warhawk87 »

Offline Soeren

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Re: Help Using a Full Bridge Motor Driver
« Reply #2 on: May 08, 2012, 08:13:25 PM »
Hi,

My first issue is that I dont have capacitors for the BOOT1 and BOOT2 pins shown on the datasheet.  I hoped I could just tie the pins to ground without too much trouble, please let me now if that thought is stupid.
If you don't use these caps, leave the pins unconnected. The caps will make the high side MOSFETs more efficient though.
Don't ground the bootstrap pins!


Secondly, I have a 10k ohm resistor connect SENSE to GND, please let me know if this is correct because I didn't really know what I was doing when I put that together.
It's not.
The motor current runs through the sense resistors, so they need to be a very low value. If you don't use them at all (for current chopping) just make them a wire link, but they're a very good safety measure if used - which means that you use the voltage dropped over them to limit current, eg. a 0.68 Ohm resistor could trigger a small signal transistor at 1A and this cold in turn be used to turn off or limit the current - value depends on needed max. current.

For testing that the chip works, ground the sense pin and don't overdo the current.


Third, with Enable tied to +5 Volts and Source to +12 Volts, the outputs produce +10 Volts no matter the combination of +5 or 0 volts given to IN1 and IN2, with the exception of IN1 High and IN2 Low, with makes OUT2 close to zero but OUT1 remains +10 Volts. 
Just fix the sense resistors and remove the bootstrap-to-ground connection and Bob's your Uncle :)
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Warhawk87Topic starter

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Re: Help Using a Full Bridge Motor Driver
« Reply #3 on: May 10, 2012, 07:06:51 PM »
Hey Soeren,

Thank you very much for your reply!  Unfortunately I made the noted corrections and was not able to achieve a different outcome.  I never actually connected the chip to my motors, but rather just measured the voltage coming from the pins with my MM.  I tested the same hookup on all 4 of my l6202, and each one gave me the same general outcome.

The in voltages are Low = 0 High = 5
The out voltages are Low = 0 High = 9 to 11 volts depending on chip used.

IN1 Low IN2 Low = OUT1 High OUT2 High

IN1 High IN2 Low =  OUT1 High OUT2 High

IN1 Low IN2 High = OUT1 High OUT2 Low

Besides for the recommended changes the IC is wired the same as the schematic posted.

If you have any other thoughts on what the problem might be please let me know!

Offline Warhawk87Topic starter

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Re: Help Using a Full Bridge Motor Driver
« Reply #4 on: May 10, 2012, 07:17:39 PM »
On a hunch I removed the grounding wire from the Vref pin and I believe it is working now...If I dont post back assume its working =D Thanks again!

Edit - Tested it with the motor, it works!  Now another question, can I PWM using this board or can I not change the speed of the motor?
« Last Edit: May 10, 2012, 07:31:49 PM by Warhawk87 »

 


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