motor controller L297... need help

l297 vref

good day... too many question to ask... please help...

this is the data sheet i need help on
https://www.st.com/stonline/books/pdf/docs/1334.pdf


i hav few questions... please help... i am using it to control 2 phase variable magnet bipolar stepper motor

1. could anyone explain to me wad is the purpose of OSC pin?.. i know it is stated as chopper rate... anyone know how to explain this using more simple term?...i dunno wad is chopper even though i read many time the data sheet D....

wad is the value for the RC circuits,,, wad is this for... n wad value i can use,, any?

2. wad is the control pin for??... it stated either to act on A,B,C,D or /INH1/2 faint

3. wad is tht /INH1 and /INH2 for?? should i use it if i just wanna control the stepper motor. please explain on this 2 pin,,, i am really headache read over n over again wthout any understanding on this...

4. and how about the SENSE1 and sense2 pin....wad is tht also...

5. how fast the frequency of the step clock can i input to the /clock pin of the L297.... does it depend on the stepper motor i use?...

6. for stepper motor, which part of the data sheet i should refer in order to know how fast the step/clock i can use wth the motor from my controller??

i would b grateful if anyone can help... u can answer part or even one question if u r really busy... any will help....

many many many thanks... in advance...

my warm regards,
sp

l297 home

1. The IC has a 'protection' mechanism that is triggered (activated) when the current exceeds a certain level (as measured by Sense1/Sense2 and compared to Vref). What happens then is that the output switches off. It is then restarted a certain time later (determined by the chopper rate, which is set by the OSC pin). This mechanism is then repeated over and over.
This basically means that, when this switching off and on again happens, that the (stepper) motor is driven by a constant current (the current sensed by Sense1/2).
The timing of this chopping is set by the resistor/capacitor value. The frequency is 1/(0.69 * R * C). With the 22kOhm and 3.3nF in the sample application this would result in a frequency of 20 kHz.

2/3. The control pin determines if either the ABCD outputs or the inhibit outputs are used to switch off the driver. Typically the inhibit outputs place the driver in a floating situation, whereas the ABCD would switch it off actively (this all depends on the driver used). In a 'floating' situation the motor keeps it's momentum, and in the active off situation the motor is being 'braked'.

4. The sense pins are used to measure the current flowing through the motor windings. This is done using a series resistor.

5. The clock input does depend on the stepper motor used. A stepper motor can only go at a certain speed before it looses torque etc. A stepper motor is typically accelerated to it's speed (if a high speed is the goal). For slow speeds no acceleration is typically needed.

6. I don't know what parameters are given in a typical stepper motor datasheet, but I think you should have a look at the steprate. There is typically a curve with the steprate versus torque (or something simular).

l297+r sense

thanxs Marcel Majoor... ur help is really appreciated n informative.... anyway, i pressed the helped button... thanks

for question num.1 so wad is the best chopper rate?... the higher the better??...

for question num.2 and 3... do u mean tht the control pin is use to select the switch off mechanism only?... b4 reading ur help... i was confuse as we would always use ABCD to control the motor... if use INH1/2.. how to control the stepper motor?..
so the bottom line is tht this CONTROL pin is use to control the motor behaviour when no clock step are input to the driver(switch off)... am i correct?

for question num.4... the sense resistors..y it use 0.5ohm?... 10ohm will works?... wad is the selection of the value?

for question num.5.....if i use 1MHz.. will the motor works?... how to determine the max frequency? Marcel Majoor mentioned tht the motor will losses its torque... i tot when frequency too high... the motor willl stall....


thanks again and again.... i m grateful

my warm regards,
sp

l297 clock

hi

here is the simulation cicuit fOr L297 how it works

stepper motor controller l297

thanxs for reply,,, could u make it more easily to read,, like pic,,,

bcos my pc hav no much space left for me to install orcad capture...

hope other will continue help answering my question... grateful

thanxs,,,

regards,
sp

vref l297

A higher chopper rate is not necessarily better. A low frequency is typically 'worse' for our ears (audible range), so this is one reason to choose a frequency like 20 kHz. If the frequency is too high then, (guessing), the current limiting becomes less effective (the motor windings are a coil ... ..).

When the (over)current becomes active the output (ABCD or INH1/2) are -momentarily- switched off (one cycle of the chopper frequency). The control pin only select which of these will be chopped (either ABCD or INH1/2). This has nothing to with the normal operations of the device. You use the device as you would normally use (just assume this current regulation mechanism does not exist). The control pin ONLY defines the action taken during 'protection' and not when no step signal is being generated.
Note: You don't need to use the current regulation feature of the device. If you don't use any sense resistors and short the sense inputs of the device to 0V then no chopping will be used at all. In that case the device only translates the clokc/direction inputs to an ABCD output sequence.

The (sense) resistor value is based on the the current 'protection' level you want. The current through this resistor generates a voltage which is 'sensed' by the L297 (Sense1/2). If the L297 protection level is set to 0.5V (Vref input) then the maximum current allowed through the motor winding would be 1A with a 0.5 ohm resistor. With a 10 ohm resistor this would be 0.05A . So, the selection is based on the allowed current through the motor winding and the Vref you are using. A typical VRef would be 1.2V (using a 1.2V reference 'zener'). If you require a maximum current of, for example 0.5A, then your resistor would be 1.2V / 0.5A == 2.4 ohm

With 1MHz the motor will definitely not run. With every clock signal the motor moves from one position to the other. The motor has to have time to move to that position before you should generate the next clock signal. It has to overcome it's mass and any inertia present. I think a few hundreds herzt as a maximum frequency is probably a very high value (and you typically have to accelerate to the maximum possible speed).
If the clock changes too fast, the motor just does not have time to move to the next position and, hence, will not move (or very slow/obscure).

l297 chopper frecuency

thank you Marcel Majoor for all the help... i am really grateful... u almost clear all my doubt,, now it is turn for me to try out myself,,,

anyway... wad is the frequency hav to do wth ear?.. or u mean analogy...

as for the ABCD and INH1/2.. i think i get it finally,,,, however, which one should i use,,, ABCD or INH1/2?? i mean i should set wad to control pin,,, which one is more preferable?...

i am connecting the Vref to my +5V... should it ok,, bcos i want max peak current,,, if i use 0.5ohm so 5V/0.5ohm= 10A... so will this 10A too large n burn some of my part?..

another one would b how i know wad is the max step my stepper motor can support... i buy from an electronics shop n the guy dunno anything bout it... the motor length is 2cm including the head come out from the motor and the diameter is bout 2.5cm... n it has 4 wire(red yellow blue brown...i dunno how to connect this also).. any idea?


thank you again,,, i really dunno how to express my gratefulness

regards,
sp

l297 c source

The frequency at which a motor (or a switching power supply for that matter) is controlled has a lot to do with the human ear. The switching of the motor (or chokes/transformers in a swtching power supply) do generate an audible sound (as if they were speakers). 'Users' don't like to hear a continuous noise coming from an electrical circuit or motor. That is one of the reasons why a frequency higher than audible for the human ear is generally preferred. Obviously there are also other reasons for selecting other frequencies, but this is just an, obvious, one.

I think you just experiment to decide which one (ABCD or INH1/2) is better. Using INH/2 reduces the dissipation in the sense resistors so this might be an obvious choise. But, it mght be that the motor runs better using ABCD-control instead of INH1/2-control. You just have to experiment.

Don't connect Vref to +5V. The maximum input is 3V!!
If you are using the +5V then at least use a resistor divider. For instance, put two 10 kOhm resistors in series and connect the ends to the 0V and +5V. The center connection then goes to the Vref input, which should be about 2.5V then (I assume the input impedance of the Vref input is relatively high).

Depending on the motor you use (and/or the capabilities of the driver/output drive), you have to set the current. You have to look at the specificatiosn of the driver and/or motor to find out which is an absolute maximum allowed current. Then set your 'protection' somewhat lower (75% ??).
If you are using the L298 as a driver, then this one can drive a maximum (!) current of 4A. The continuous current for this device is 2A, so in this case you would set the 'protection' to 2A (2.5V/2A = 1.25 ohm).

Figuring out the connection for a stepper motor should be not to difficult, but be aware that their are different type of stepper motors. Unfortunately I don't have the information by hand on how to find out the connections.
For the maximum speed concerned; this can be determined by experimentation. By slowly increasing the speed (clock frequency) you should easily be able to determine at which speed it still runs correct and at which it does not (be sure to connect the mechanical 'load' to the motor when testing...)

limit curent l297

dear Mr. experience,

thank you again,,,, but my question continue,,,, please b patient wth me.... hehehe

Don't connect Vref to +5V. The maximum input is 3V!!
If you are using the +5V then at least use a resistor divider. For instance, put two 10 kOhm resistors in series and connect the ends to the 0V and +5V. The center connection then goes to the Vref input, which should be about 2.5V then (I assume the input impedance of the Vref input is relatively high)

Click to expand...

fortunately u mention it... i tot 5V would b ok,,, how u know maximum is 3V??

if i use voltage divider...will it increase the losses too much as current may flow in any condition?...


for this paragraph....

Depending on the motor you use (and/or the capabilities of the driver/output drive), you have to set the current. You have to look at the specificatiosn of the driver and/or motor to find out which is an absolute maximum allowed current. Then set your 'protection' somewhat lower (75% ??).
If you are using the L298 as a driver, then this one can drive a maximum (!) current of 4A. The continuous current for this device is 2A, so in this case you would set the 'protection' to 2A (2.5V/2A = 1.25 ohm).

Click to expand...

for the absolute maximum I for L298,,, i look at the data sheet but i only can find the "TOTAL DC CURRENT UP TO 4 A" at the intro on the front page of the data sheet... i cant seems to find it inside the data sheet... which specification mention the max allowed current?

this i just wanna make sure... for 75% of 4A... it should b almost 3A.. why u mention 2A??

hope i am correct assuming "(2.5V/2A = 1.25 ohm)" is to find the sense resistor...no???.......... (and if Vref can support 5V... and i want 3A... so 5V/3A = 1.6667 ohm.. so i find my sense resistor... yes?)

i think i start to understand tht the sense resistor is to cutoff the current when it is over the limit set by user...for "2.5V/2A = 1.25 ohm" the max current is 2A... over then it is cut out....correct??

if the L298 can support 4A but my motor can only support 2A.. is it ok to just use 4A?...or this maximum current is depend on the voltage n load condition (ohm's law) so it doesnt matter....
wad i mean is tht the max current is not a constant current supply to the motor,,, it is just the max current available tht the motor can eat up (if the motor request more than 4A, the L298 will say sorry; and if the motor request less, L298 supply less).. am i correct again??

the last part u teach how to find the motor max speed,, it is brilliant...

thank you Marcel Majoor and everyone helping ... thanks lot.... really grateful..
(when u think u solve a problem, u might just create another, so many question :lol: really hav to ask... i am in doubt)


my warm regards,
sp :lol:

l297 problems with cw

The absolute maximum of 3V can be found in the datasheet of the L297. It is a simple as that. Look at page 7 of the datasheet, electrical characteristics of the Vref input - min 0V, max 3V .......
Thus, never put 5V on the Vref input. This might (will) destroy it!
The sense resistor calculations are based on the law of Ohm: U = I * R, so calculations are simple, assuming you know the Vref you decided on (< 3V !!) and you know the maximum current you want to allow.
The sense resistor is not used to cutoff the current directly (although it -will- limit the current flowing based on Ohms law), but the sense resistor is used to measure the current flowing through the motor winding. This is done by converting this current into a voltage (by means of the sense resistor). This voltage then goes to the sense input of the L297, where it is compared with the Vref voltage. If it is higher, then the driver outputs (ABCD or INH1/2 depending on the control input, you remember) are temporarily switched off.

A voltage divider always draws some current, but the current depends on the resistor values choosen. With 2x10kOhm this would be 5/20000 == 250 uA which is negligible . Even if you have to use 1KOhminstead of 10kOhm this would still be 2.5 mA, which should be no problem for the +5V power supply.
Instead of a voltage dvider you can use a voltage reference IC (e.g. which generates 1.2V or 2.5V). This makes the Vref more stable, but these devices also draw some current ....

On page 2 of the L298 datasheet themaximum rating are also beding shown. There is also additional data (under 'Peak output current), like 'Non repetative', and 'DC'. This 'DC' is the allowed current when the device is continuously on
The reason for 2A is that you typically want to be in the safe 'area' of the device. This is, at all times, 2A (assuming the devices is being cooled the way it should). Thus if you use 2A as your 'protection' base (disregard the 75% in that respect) then you should be fine. Don't try to draw 4A out of the device. This is an absolute maximum .... Even 3A is only allowed 'Non repettive'.
Thus, use 2A as the 'protection' in your design (note: this 'protection' is then only used to protect the L298 driver - if the motor has a lower maximum current then you should design for that limit).
BTW: It is the L297 which limits the current (by the chopping mechanism), based on the sensed voltage and Vref. The L298 does not limit the current in any way.

l297 simulation

sorry... i was looking at the application note of the L297,,,, tht's the prob... sorry...

thanks again,,,Marcel Majoor... i press the helped anyway...

if i am using 2.5V (voltage divider)... i can't use 0.5ohm as it shows in the data sheet for R(sense).... if i want to hav 1A... so R(sense)=2.5V/1A=2.5ohm... correct?...

anyway... could u tell me bout the clk timing... as u can c from the bellow pic... y the tclk time is just on the low pulse,,,, wad it means?..

if the tclk is shown... can we determine the clk period??....i think this is the fastest posible clk pulse allowed....

it seems like u are teaching me how to understand the datasheet....hehehe

Thank you.... i am grateful....

my regards,
sp

pull up l297

The 2.5V/2.5 ohm == 1A is correct.

From the 0.5 us in the datasheet you could conclude that the (max) clock is 1 MHz (0.5 us low/0.5us high signal).
However, you should not be bothered about this, because this maximum is far (and I mean faaaar) beyond the capabilities of the steppermotor. Assuming you have an *ideal* steppermotor, only then you would we able to run at this frequency. Simple calculation dictate then, that with 1 Mhz, the steppermotor will do 1000000 steps/s. Assuming you have a stepper motor with 250 steps/revolution this is 4000 rotations/s == 240000 RPM ........
Unfortunately we don't deal with an ideal stepper motor so the maximum frequency you will actually be using willbe in the few hundreds Herz ... (just guessing here).

The L297 'steps' on the rising edge of the clock input.
The 'setup time'/'hold time' and such you see in the datasheet means that you can't (should not) switch the other signals at the same time as the clock signal. They need to be present a certain amount of time before the clock signal is activated, and need to be present some time after the clock signal is removed. Typically you don't have to bother about this at all, since these signals (CW/CCW/HALF/FULL) are fixed level signals. You don't change them all the time. Only the CW/CCW signal is changed, for changing directions, and an 'incorrect' timing would only mean that you would do one or two false steps.

what is clock in l297

sorry for asking again... need help on the "HALF/FULL_NOT" pin

as listed on the L297 DS... as bellow...

there are 3 type...half step op, One-phase-on full step mode, Two-phase-on full step mode...

the half step is ok, just set the "HALF/FULL_NOT" pin to '1';

however, for the "One-phase-on full step mode" and "Two-phase-on full step mode" how to select one of it?...set the "HALF/FULL_NOT" pin to '0' and the 2 mode depend on your luck??????? like it mention there it depend on the translator state, can the translator state b controled?..

hope someone can help....

many many many thanks...

regards,
sp

l297 y driver de 10a

You have to know the state the L297 is in. This can be detected using the HOME output of the L297. When this output is active you know that the L297 internal controller is in state 1. Once you know this, and because YOU control the steps (clock), you also know in which state the L297 (should be), and when to switch to the correct FULL STEP mode.
Note that you should do this 'synchronization'/'detection' in HALF STEP mode, since in this mode all states are 'used'.
You can also use another approach. When you set the FULL STEP MODE then the HOME output is activated only when the NORMAL DRIVE MODE is active. The HOME output is not active when WAVE DRIVE MODE is active. Thus, set FULL STEP mode, do 4 or more steps and when the HOME was activated then NORMAL DRIVE MODE is active. If this is NOT the mode you want then switch back to HALF STEP mode, do 1 step, switch to FULL STEP mode and check again. This time it should be the correct mode.

différence osc ou clock l297

wow! u are great... thank you....

from wad u say... so the full step mode cannot b control using mechanical switch as the motor move so fast...

so it would only feasible to control it using the controller....

actually yesterday nite i already can run the stepper motor,,, but one prob is the cw/ccw_not... i change to ccw using switch... but the motor doesnt wanna change direction,,,


thank you again...

warm regards,
sp

what is chopper l297

The FULL STEP mode can be controlled by mechanical means, but you still need some logic to make sure the correct full step mode is switched on.
OR .... if you also use the RESET input then you know that, after a RESET, the controller is in state 1 ('HOME').
So, using the RESET input of the L297 you can also set the correct mode, without using the HOME as feedback.
NORMAL DRIVE MODE: set HALF STEP mode, activate RESET, de-activate RESET, set FULL STEP mode
WAVE DRIVE MODE: set HALF STEP mode, activate RESET, de-activate RESET, do one step (1 clock cycle), set FULL STEP mode

Changing directions is typically done at 'zero' speed of the motor. If you use a mechanical switch make sure that is (preferably) debounced, and that you swith from one level to the other (switch-over contact). Alternatively you could use a make or break contact switch (instead of a switch-over) and use a passive resistor (10k) to +5V. You let the switch then shorten the CW/CCW input to 0V.

reset l297

thank you x 1000 Marcel Majoor... again

wth "HALF/FULL_NOT" set to '0' and after reset_not for L297 is press and release... the home state(0101) start.... so this "NORMAL DRIVE MODE " is easily enter...

but for "WAVE DRIVE MODE" after reset_not ,,, waiting for one clk cycle is imposible for mechanical switch?... i think tht cannot do....

this is ok,, i can live wth the normal wave drive mode.... but the open collector output of the "home"... i cannot read from this pin, i dont understand why ... when it reach the 0101 state "home" will b '1' or '0'??

for the cw/cww_not.. the problem solved D,
the "app_note in L297" use a 470uF btween the power supply pin and gnd pin of L298N, but i dont hav the 470uF, so i used 10uF instead(my mistake)... the motor so weak n it cannot change direction....
after i plug out the capacitance, everything work supperb...
and the change direction is synchronously, so u can change anytime u like

another question is regarding the voltage drop for L298N... i use 15v from adapter(ac to dc) and it drop to 8-9V after the motor start to run....
so for this, should i use a voltage regulator to make it constantly 12V?...i prefer 12V
actually under my observation, the motor run better wth higher voltage(btween 9-10V).. 12V constantly should b better?...

the cheap stepper motor cost bout USD3.5(max almost 1000 steps per second, i try it out myself).... and everytime i assert the reset_not(L297)... the motor need some time to settle down,,, it shakes(not spinning well) a lot before it cool down and run properly, higher voltage shorter the time to settle down.
so 12V voltage regulator required? or a 9V one?

and for the "control" pin... it make no diff(high or low) on the performance....any comment?

should i buy better motor so tht it doesnt shake tht muchafter reset_not.. is quality the problem here?


thank you again.... i am grateful again.. hehehe...

my warm regards,
sp

chopper frequency l297

Using a mechanical switch to select the mode is, basically, only possible with some dediacted hardware added. So in your situation I don't think it is a possibility.

Since the HOME output is an open-collector output, it floats when it is inactive. This means that if you want to measure the signal that you need a pull-up resistor (e.g. 10 kOhm) to +5V. This way you will measure 5V when the L297 is in it's initial state , and 0V otherwise. Thus, only with a pull-up resistor you will measure a '1' (HOME) or '0'. Without it you will either measure a '0' or a floating signal (which most of the time also 'translates' in a '0').

The 470 uF you mention is the 'buffer' of the power supply. The actual value depends on the current drawn from this power supply by the motors. Typically, the larger the better. The 10 uF you used does not 'buffer' that much (meaning that the voltage drops or becomes more erratic/changeable). When you removed the 10 uF the voltage probably dropped even more.

Using a regulator will not make the voltage become higher. Only a buffer capacitor (like the 470 uF) can make some difference here since it will provide additional power when a temporarily higher power is needed by the motor and which the power supply can not always provide (fast enough).

Most of the erratic movements might be due to an irregular voltage. A constant voltage is always the best. This does not necessarily need to be a regulated voltage (the motor does not really care if it has 5V or 5.5V ....). This constant voltage can be created using at least a large buffer capacitor. Obviously the power supply you use must also be able to provide enough power/current to the motor without a decreased output voltage. If you have a good power supply, and not connected that far away from the electronics then you can omit the buffer capacitor, or at least use a smaller one.

The CONTROL function is that it will chop the output only when an overcurrent situation occurs. If the current is lower than at what the chopper operation is set to, then you won't notice anything. And even when the chopper 'kicks' in, this might not be too obvious when looking at the motor (it should still functions as normal, only the 'torque' the motor can generate is less because the power applied to the motor is reduced by the chopper).

So, check if the power supply can generate the voltage and current the motor requires (without knowing the requirements of the motor things will stay 'experimental').
If not, use another power supply - a buffer capacitor is always a good idea but with a good power supply not that critical. During operation of the motor the voltage should not drop too much (this would indicate that the power supply can not supply the required current). If the voltage drops more than 0.5 - 1V (just guessing here) then I would suspect an 'underpowered' power supply.

Bottom line: You probably need a better power supply. Use a buffer capacitor. Check for the correct voltage for the motor (a few volts too high is almost never a problem).

how to control stepper motor with l297

thank you x 10... again...

for the "home" i understand D.... however the low output voltage level is 1.2-1.5V(using 1Mohm)... but my controller can only accept the max low is 0.8V(Vil)...
wad should i do?...i think this is the prob tht i cannot detect the change on this output...

for the buffer u meantion... can u look at the the diagram on my topmost first post....
there is another 100nF(C3) connected wth parallel wth the 470uF,,, wad is the purpose on this so-many-capacitors?... a 470uF is not enuff?..

i can change the direction of the motor,,,, but after a while,,, nth works anymore,,, i hav no idea wad is the problem... is it the prob wth the voltage from the adapter?..
sometimes it can,,, sometimes it cannot,,, i am really sick of it
i check the input to the CW/CW_NOT, it is asserted properly so it is not mistake-connect prob..
wad can i do?..

is it also my lousy motor quality?... when i tried wth 1000 steps/s the motor spin more smoothly... but wth my hand,,, i can change the direction to wadever direction i want,,, it doesnt seems like following my direction switch...

this is good one... i am sick of this lousy motor....
but i do learn a lot(from you)...

thank you again... please help

warm regards,
sp

sense resistors l297

The reason for a smaller and a larger capacitor is that the smaller capacitor is used to filter out the higher frequencies and the larger for the lower frequencies (or in your case to buffer the power supply). A capacitor has a certain resistance at a given frequency (impedance). With a given frequency the resistance of a smaller capacitor is lower than that of a larger capacitor and will therefore 'shorten' the signal more to ground than a large capacitor. The higher the frequency, the lower the resistance, the more the signal is shortened to ground.

The HOME output should have no problems getting the signal low enough (the datasheet mentions 0.4V as a maximum). However, be advised that using a pull-up resistor of 1 MOhm is not typical. A typical pull-up is more in the 10 kOhm .. 100 kOhm range (depending on fast/steep the pull-up should be). I would use a 10 kOhm resistor. You can use a pull-up which is as low as 1 kOhm (not advised though), and still you should have a 0.4V output (max) when the HOME output is active (meaning NOT HOME). When the HOME output is inactive (meaning HOME) the level should reach the 5V the pull-up is connected to (maybe 1V lower). This is the situation when the HOME output is not conencted to anything (except the pull-up resistor). Check this first. If this is correct, then connect the HOME output to the circuit you use for detection and test again. You probably will experience some different values, but the 0.4V 'low' voltage should still be possible (the HOME output can sink at least 5 mA without getting above the 0.4V level -> if not the circuit connected to the HOME is probably not correct).

If you have a 'bad' power supply you can get bad results. Also, when driving the motor too fast, the torque of the motor is very low and thus the motor can easily be stopped by 'external' means (a finger touching the motor). The only way to get the motor restarted is then typicall to lower the frequency which drives the motor. A stepper motor can only be run at a relative low frequency when no acceleration is used! I would advise to use a much lower frequency than the 1000 Hz you are using. Try it at 100 Hz and see if the motor behaves in the same way as it does at 1000 Hz.