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Rather than getting into a long winded discussion on the functionality 
of this device, have you looked into the application and tech notes on 
the ST web site. Putting aside the marketing waffle that is present in 
all data sheets, the app notes and tech notes are very good.

http://www.st.com/stonline/stappl/productcatalog/app?page=stcom/PcStComTlMainMenu

Yes, every one will give more than likely only half the answer. The 
other half will come by reading the app and tech notes. There is even a 
good app note describing catastrophic failure conditions which the L297 
will not protect against. Rather than just concentrating on the L297, 
have a look at app notes for bridge drivers. The L297 is only half the 
story.

Regards,

Antonio Benci.

Jinx wrote:
> I'm looking into the inner workings of the L297 stepper motor
> controller, specifically to find out how the chopper works
> 
> The camera pan unit I'm building (recent [PIC] thread) has at the
> moment all components - PIC, L297, L298, and motor - using 5V.
> I'd like to be using 12V for the motors to get the step rate up
> 
> The ones I will be using are Type 17 bipolar, 9.6V, 0.4A, 24 ohm
> coils. ISTR measuring the inductance at 10mH, but can't be sure
> 
> So, Googling around, I find a lot of pages by people who know that
> the L297 has a chopper (and kind of proudly imply they know how
> to use it), but offer the same standard datasheet application schematic
> with no further explanation. Many dead-end discussions in forums
> between people who frustratingly know only half the story and stop
> short of saying anything useful. Admitedly some do have a stab at it
> but there's a lot of waffle to wade through, and mistakes I've seen
> in some parts don't inspire confidence in the rest
> 
> Fuzzy diagram, great colour scheme ;-/
> 
> http://www.societyofrobots.com/member_tutorials/node/168
> 
> Jones has a very good page on current-limiting theory, which should
> be helpful once I can apply it to a specific IC and set of conditions
> 
> http://www.cs.uiowa.edu/~jones/step/current.html
> 
> This ST pdf looked promising
> 
> http://measure.feld.cvut.cz/groups/edu/y38pmm/1650___AN468_stepper.pdf
> 
> Ultimately a bit of a tease. For example, the unexplained
> 
> "Where several chopper drives are used in the same system, they
> should be synchronized to prevent intermodulation effects"
> 
> and the voltage divider in Figure 5 with no calculations
> 
> I'm quite prepared to put the legwork in myself with a board, a motor,
> a PSU, and a lot of tinkering, but does anyone have a good reference
> to chopping high voltages with an L297 ? Including perhaps, probably
> unlikely, comparison graphs of step rates vs supply vs motor specs
> 
> The sort of thing you'd find on a "Everything an L297 + L298 can do
> and how to do it" page
> 
> Which I'd happily write up for the PICList site
> 
> TIA
> 


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