I am trying to use the VNH2SP30 on a micro with 3.3V levels, but it doesn’t seem to work. I assume that I don’t reach the 3.25V required by the motor controller. What can I do to boost my level, but maintain the pwm signal - in other words, how do I interface the motor controllers to my micro?
Any help is greatly appreciated!
That sounds like a good guess as to the source of your problem, and one simple solution would be to use a small transistor circuit with two current-limiting resistors to amplify the voltage of your PWM signal:
You can use the common PN2222 resistor, or a similar NPN transistor, or even a PNP transistor so long as you keep in mind that it will invert your PWM signal. Resistor values will depend on what transistor you use, and what your supply voltage will be, but we can make some good guesses.
The Base resistor isn’t 100% necessary since your microcontroller will only be able to supply a limited current to the transistor, but it’s good practice to include one. 1Kohm should do the trick, you don’t want to go too high or the transistor won’t fully [i]switch[i] on.
The collector resistor is more important, since it is protecting the input of your motor controller, and too much current will damage the chip! The spec sheet says you need at least 1uA, and an absolute max of 10mA (we don’t even want to get close to the abs max!). If you’re using a 5V source, another 1Kohm resistor will limit your current to less than 5mA (I say less than because there will be some votlage drop from the collector to the emitter of the transistor). This would be a good solution if you’re going to Radio Shack and paying $0.99 for a five pack of resistors. If you have an assortment of resistors around, or you feel like splurging $6.29 for the 100 piece assortment at Radio Shack (or $12.49 for the 500 piece assortment, gasp!), you might want to limit the current even further to about 1mA with a 4.7Kohm or a 5Kohm resistor.
If you want to use a higher voltage than 5V just remember to scale your collector resistor accordingly, remember V=IR! Good luck!
-Adam
