L298 Motor Driver

Log in or register to post comments
Go To Last Post
7 posts / 0 new
Author
Message
reSpawn
reSpawn's picture
Level: Wannabe
Joined: Sat. Jun 9, 2007
Posts: 62 View posts
Location: Romania, Oradea
#1
Posted by reSpawn: Wed. Jan 14, 2009 - 07:20 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

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.

Tags:

Learning and Information, General Electronics, ATmega8
Top
ka7ehk
ka7ehk's picture
Level: 10k+ Postman
Joined: Fri. Nov 22, 2002
Posts: 21793 View posts
Location: Tangent, OR, USA
Posted by ka7ehk: Wed. Jan 14, 2009 - 09:57 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

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

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

Top
reSpawn
reSpawn's picture
Level: Wannabe
Joined: Sat. Jun 9, 2007
Posts: 62 View posts
Location: Romania, Oradea
Posted by reSpawn: Thu. Jan 15, 2009 - 08:46 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

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.

Top
reSpawn
reSpawn's picture
Level: Wannabe
Joined: Sat. Jun 9, 2007
Posts: 62 View posts
Location: Romania, Oradea
Posted by reSpawn: Thu. Jan 15, 2009 - 07:25 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

The updated schematic:

Nicu reSpawn.

Top
wg0z
wg0z's picture
Level: Wannabe
Joined: Mon. Sep 15, 2008
Posts: 77 View posts
Posted by wg0z: Thu. Jan 15, 2009 - 07:40 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

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

Top
emuler
emuler's picture
Level: Raving Lunatic
Joined: Wed. Feb 7, 2007
Posts: 2348 View posts
Location: New Delhi, India
Posted by emuler: Thu. Jan 15, 2009 - 07:48 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

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.

Top
reSpawn
reSpawn's picture
Level: Wannabe
Joined: Sat. Jun 9, 2007
Posts: 62 View posts
Location: Romania, Oradea
Posted by reSpawn: Thu. Jan 15, 2009 - 10:12 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

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

Nicu reSpawn.

Top