L298 Motor Driver

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Hello everyone!
I'm trying to build a pcb for an L298 and I need your suggestions and help again :)
I want to drive a single DC Motor with this driver using PWM from an Atmega8.
Here is the schematic which I want to improve:

Just ignore the "1N5908" diode, I will be using 1N5822 instead.
While I was looking at the datasheet( http://www.st.com/stonline/books... ) I found at page 7, some suggestions and as I have no electronics background I don't quite understand what the following means:

Quote:

A non inductive capacitor, usually of 100 nF, must
be foreseen between both Vs and Vss, to ground,
as near as possible to GND pin. When the large capacitor
of the power supply is too far from the IC, a
second smaller one must be foreseen near the
L298.
The sense resistor, not of a wire wound type, must
be grounded near the negative pole of Vs that must
be near the GND pin of the I.C.

Do I have to put two non inductive capacitors, one between Vs and GND, and one between VCC and GND ?
Sense resistor? What's the deal with it? I've google'd and found some schematics using L298 IC and two I've found had a direct connection between SENSA,SENSB and GND. Where is the resistor?
Another thing I don't quite understand, one schematic had a resistor wired to the E1, and E2, then to the control pins from the Atmega. Why is that?

Nicu reSpawn.

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The sense resistor provides a way to monitor the motor current. You do not need it and the sense pins should be connected directly to ground, otherwise.

The way I read the text, they are asking for TWO caps. Now, at the range of frequencies that are present in this circuit, "low inductance" usually simply means ceramic surface mount. Ceramic disc should also be adequate. You would NOT want to use a film (or other tubular) cap (which has much higher inductance).

There is no good reason for a resistor between the micro and the enable pins. The enable pins can tolerate any input voltage from -0.3V to Vss. It does appear to be a standard TTL input, which means that it does draw a little current when pulled all the way to Vss, but the micro won't care.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Hello Jim, I don't know much about electronics, but I've read somewhere that is a good habbit to "tie"(?) the pin to a known state while the atmega is starting. Do you know something about this?
Regarding the sense resistor, I can hook them up somehow(?) to an ADC pin and read the ADC value then interpret it and I know how much current the motor draws?
What about the schematic? Any errors you guys see?

Thanks in advance :)

Nicu reSpawn.

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The updated schematic:

Nicu reSpawn.

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l293 has internal (non-zener) clamp diodes,
so your external zeners may not be necessary...
unless the load is high-inductance ?!?

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Why are you using zener diodes at all? When will the zener action ever come into play? The diodes are for clamping the output lines to the power supply lines. Use regular diodes, or better, use Schottky or Fast Recovery diodes.

If you think education is expensive, try ignorance.

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Just ignore the "1N5908" diode, I will be using 1N5822 instead which are Schottky.

Nicu reSpawn.