L297 & L298 Voltage problem


I have connected the L297 & L298 as showed in the datasheets with 470uF near the L298 and 100nF near the 5V supplies (and 2 at the 7805, which supply the logic circuits).
My main supply is ~8V, which I supply the L298 with (for the motors, 5V for the logic).

And here is my problem:
When I enable the L297, the voltage in the logic circuit rises to ~6,6V.
When the L297 is not enabled, there is 5,0V.

If I change the main supply, the 6,6V follows accordingly (drops/ rises).

How can this be?

I've read the long thread in this forum conserning the L297, and it was very helpfull for my understanding, but the problem remains.

I use BYW56 diodes for the motor if that has anything to say...

I'll be grateful for any reply that can guide me in the right direction.


Hi again.

I made some further measurements, and found that connecting pin 6 and/or 8 on the L297 (B and INH2) will make the voltage rise above 5V...

That is really strange! :S

I had gone through the long discussion on L297 and L298 stepper controller circuits and wired up my own board. But the L297 IC stops working after a couple of runs.
Could anyone tell me what could be the reason?
I have used schottky diodes as protection diodes.
Thanks in advance


a picture of how you have it wired would be good. If the L297 chip is burning up, my guess would be that the motor power supply voltages used in the L298 are feeding back into the L297...


i have sorted out the problem... the supply terminals had got shorted
now it is working but the output voltage is 2.89V only
i have used +5V for L297 and +12V for L298
and i have used a 1k trimpot for Vref

now my L297 L298 board is working but the output voltage is 2.89V only...i have tried it for the past few days to see if any problems are arising, other than the low voltage there are no other problems,what could be the reason for the low voltage?
could someone help me out?
i have used +5V for L297 and +12V for L298
and i have used a 1k trimpot for Vref


there are a thousand possibilities for what could be wrong... pictures are pretty much the only way for us to see what it might be!


PIctures would definately help -- but also check the current limits of the chips you are using.

7805 tend to be 1A limited (max, some less) and tho you are not driving the motors with them (as you describe) these limits can cause problems when motors start and stop -- even with the decoupling caps you describe.

Heat sink every chip you can -- a piece of aluminum (nothing fancy) to the metal tab of every chip that isn't a surface mount will also help alot. 298s can take a lot of current but do get hot -- check to see if this is a problem. i have not used 297s -- but the dip pacjage may be heat sinkable through ground -- look at how heat sinking is handled with a 293d.

finally put a really big cap across your power supply near your arduino -- sometimes back emf can cause brownouts and sometimes big caps make this go away.

the sad truth is something may have fried -- and then ignore all of the above and go shopping.

good luck