I am building a stepper motor driver that will be pulsed and direction-controlled by a PICAXE - probably a 40X2 given the other aspects of the system. The driver is quite straightforward and is based upon an L297 stepper driver and an L298 H-Bridge and works just fine.
The L297/L298 combination permits current-limiting regulation by applying a voltage (1-3 volts) to leg 15 (VRef) of the L297 driver http://www.st.com/st-web-ui/static/active/en/resource/technical/document/datasheet/CD00000063.pdf . This is mostly done by using a straightforward potentiometer and voltage divider from +5V.
My application requires the stepper motor to operate with varying levels of torque; sometimes it will be loaded and require max amps through the windings, but when it is stationary it will not have much of load to resist and therefore could operate with the current quite markedly limited. Therefore I am thinking of using the PICAXE DAC to drive the 1-3 volts needed at VRef of the L297. My question is whether or not this needs an intervening Op. Amp. or whether the DAC output could drive this directly. Obviously I realise that I should look up the parameters for the current requirements of the VRef pin, input impedance etc., but all that I can find is a note that the "comparator bias current (pin 15) = 10uA" . Clearly I could just wire it up and try it, but even if it works I guess that it might be overloading the DAC output and cause damage at some point later.
This seems a perfect application for the PICAXE DAC. Expert technical opinion would be much appreciated.
The L297/L298 combination permits current-limiting regulation by applying a voltage (1-3 volts) to leg 15 (VRef) of the L297 driver http://www.st.com/st-web-ui/static/active/en/resource/technical/document/datasheet/CD00000063.pdf . This is mostly done by using a straightforward potentiometer and voltage divider from +5V.
My application requires the stepper motor to operate with varying levels of torque; sometimes it will be loaded and require max amps through the windings, but when it is stationary it will not have much of load to resist and therefore could operate with the current quite markedly limited. Therefore I am thinking of using the PICAXE DAC to drive the 1-3 volts needed at VRef of the L297. My question is whether or not this needs an intervening Op. Amp. or whether the DAC output could drive this directly. Obviously I realise that I should look up the parameters for the current requirements of the VRef pin, input impedance etc., but all that I can find is a note that the "comparator bias current (pin 15) = 10uA" . Clearly I could just wire it up and try it, but even if it works I guess that it might be overloading the DAC output and cause damage at some point later.
This seems a perfect application for the PICAXE DAC. Expert technical opinion would be much appreciated.