L297 Stepper Dirver

What voltage are you using for the L298 supply?

Although the motor is rated at 12V, you'll need a much higher voltage (say 36V) for the supply when driving fast - with only 12V, you can't get the motor current up high enough during one step period (because of the motor inductance). Don't worry about overloading the motor, the L297 is a chopper - i.e. it monitors the motor current and switches off when the current has built up high enough.

I've got a drawing of a simple L297/L298 circuit which works very well. Unfortunately it was done back in the days of pen-plotters, with an ancient software package that needed a (now-broken) hardware dongle. I could send you a scan if you like.

I've got an excellent ap note in an old ST book (1987) - I'll try to find an on-line copy & give you a link.

Lots of stepper motors don't like to be started at elevated step rates, and many manufacturers have papers on the need to ramp up the speed -- especially through resonant frequencies. Sounds like that's what you may be dealing with.

Thanks both of you for responding so quickly!

Motor driver is supplied with 24v.

Current sense is set for 1A (1R/2W resistor) with 1.2 v reference voltage at L297 pin.

And one more thing i would like to share with you that is:

When stepper motor gets stall (i.e. one phase continous ON), the l298 gets heat, is it normal behavior? because it does not get that much heated upon running operation of the motor.

Thanks & Regards!

We used the circuit above for setting the current. When running, the DRIVE input is pulled low, and RV1 sets the current. When the motor is idle, DRIVE is taken high, and RV2 is used to set a holding current, reducing motor heating (and wasted power). (Please ignore the TR1 legend - it crept in when I clipped this bit of circuit out of the bigger drawing).

(We also had the circuit to reduce each phase current by 70% when both windings are on, to give smoother driving - I haven't shown this, but I'll post it if you're interested.)

I still wonder if your 24V supply is high enough. Can you get a 'scope on one of the L297 current sense inputs, and check that it's getting up to Vref quickly enough at high step rates?

Hi!

Ofcourse interested.

Now I think i should provide 35 or more to the motor

I hope you can make this out - it's a pretty lousy image. Do you have anything that will open a DXF file? If so, I'll send you one.

Most stepper motors do not require 24 VDC, so the L298 is switching on and off to attempt to maintain no more than 1 amp through the motor, but it's always being cut off by the current limit circuit and not by command signal. It may not switch off as efficiently that way. In the dynamic mode, all channels are switched by command and the inductance of the windings probably keeps the current from reaching 1 amp before the phase is turned off and then next phase is switched on at some minimum frequency. At very low frequencies, the current may reach 1 amp limit in each phase, but it doesn't persist. Nevertheless, the L298 will probably run hotter at slow speeds than at higher speeds. Maximum current is reached after 5 time constants of the resistive-inductive circuit.