Troubles with L297/L298

[ragrillo]

Hi
I am a new user of stepper motors (bipolar) and I am trying to work with the L297 controller and the L298 driver. I am setting the the L297 in the two phases on mode.
The circuit I am ussing is the recommended in the Application Notes of SGS - Thompson.
I was able to manage the L297. It means I had get the outputs I was expecting from the controller, (in pines Inh1, Inh2, A, B, C and D while I move the clock manually) but I did not get the necessary voltage in the winding pins (2 - 3 and 13 - 14 of the L298).
The voltage I get between the ends of the same coil were, different of zero, but similiar between them, that means that never circulate any current through the windings.
As I place Control in High level, for Phase chopping, I thought the problem could be in the sensing current circuit. To avoid that problem, I connected the pins 13 and 14 of the L297 to Gnd and a pair of 14 ohms resistences instead of the windings and 20 Volts to the Supply Voltage (Pin 4 of L298), to be sure the curent wasn´t never higher than 2 A, but nothing change.
I had change several L298 chips, foresighting they were burned, but nothing changed.
I am sure I am making something wrong, but I don´t know what additional things can I do. I will appreciate very much any help.

Raul

[pminmo]

Raul,
How hard is it for you to remove the L297 from the circuit? I assume you have checked power and gnd to the L298? If you can easily remove the L297, I would suggest putting a pair of load resistors to simulate the motor. Test one output by a voltmeter across the load from out1 to out 2. With ena low, there should be no voltage reading (<.2v) from out1 to out2 regardless of the state of in1 and in2. When in1 and in2 are in oposite logic states you should read your power supply voltage minus a couple of volts, reversing the opposite states on in1 and in2 should reverse the polarity of the voltage reading. For example if you motor supply voltage is 20, in one state I would expect approximately 18V the opposite state it would switch to -18V.

Phil

p.s. we have a single sided pcb available here:
layout: http://webpages.charter.net/pminmo/L297_8board.pdf
Schematic: http://webpages.charter.net/pminmo/L297_8schematic.pdf
Copper for pcb: http://webpages.charter.net/pminmo/L297_8copper.pdf

The pcb is for toner transfer home brew pcb's

[ragrillo]

Phil

Thank you for your answer.

I had remove L297 from the circuit, then I am going to check if my schematic is the same you mentioned and will make the test.
Raul

[ragrillo]

Phil
I have remove the L297 from the circuit and checked the power, the ground and the +5V control voltage in the L298.
When In1 and In2 were in opposite logic states and EnaA high, no tension is reading between out 1 and out2. The same thing happens with In3, In4 and EnaB.

I work with a power voltage of 25 volts with a load of 15 ohms in the outputs.

I have changed several L298 thinking they were burnt and, if this is so, I do not understand why it happens. I am lost.

Raúl

[pminmo]

with no power applied, measure the resistance between in1 and in2 with no 15 ohm resistor.

Phil

[ragrillo]

Phil
The measured resistance between in1 and in2 (pin 5 and 7). It is >10 Megaohm. The same thing happen between in3 and in4 (13 and 14), out1 and out2 (2 and 3) and out3 and out4 (13 and 14).

Raúl

[pminmo]

Ok,
Make you measurements on the pins of the 298 directly. No power applied, assuming the multiwatt package:
1. Measure resistance between pin 15 and pin 1. should be low resistance < 5ohms
2. Measure resistance from pin 15 to pin 8. should be low resistance < 2ohms
3. Measure resistance from pin 1 to pin 8. should be low resistance < 2ohms
With power:
4. Measure dc volts at pin 9 to pin 8(negative) should be 5.
5. Measure dc volts at pin 4 to pin 8, should be 25.

Phil

[ragrillo]

All the readings are OK

Raúl

[pminmo]

With power applied, no load on the out1 or out 2 lines.
1. Jumper in1 and ena to 5v out 1 should be (S/B) approximately 24vdc to pin 8.
2. Leave ena to 5v and jumper in1 to gnd, out1 s/b less than 2V to pin 8.
3. Jumper in1 and ena to 5v out 2 should be (S/B) approximately 24vdc to pin 8.
4. Leave ena to 5v and jumper in1 to gnd, out2 s/b less than 2V to pin 8.
5. Jumper in3 and enb to 5v out 3 should be (S/B) approximately 24vdc to pin 8.
6. Leave enb to 5v and jumper in3 to gnd, out3 s/b less than 2V to pin 8.
7. Jumper in4 and enb to 5v out4 should be (S/B) approximately 24vdc to pin 8.
8. Leave enb to 5v and jumper in4 to gnd, out4 s/b less than 2V to pin 8.

Phil

[ragrillo]

In all the cases the outputs were between 0.6 to 1.5 volts, but it seems there are “floting” outputs, because the values are changing permanently.. The voltage between out 1 and 2 and between 3 and 4 is always, is in all the cases between 0 and 1.6 volts.

I read the applied voltage in the pins. There are no doubts they were applied.

L298 is just e little bit warm.

Raúl

[pminmo]

Raul,
I'm starting to be baffled. Do you have a schematic of the circuit you built? How about a digital picture of your board?

Phil

[ragrillo]

Phil
I am sending a doc, where I pasted the schematic of the circuit I built. I am sending a zip file with an Autocad drawing with the schematic, and a PCB of my board. In the schematic, the upper right corner is just a set of optically coupled isolators to avoid noises in the microprocessor board.
There is a light difference between the PCB and the Dwg. files. The actual board is like the schematic.
I hope yuo can open this files.

Raúl