I'm trying to connect 5v supply to a L298N motor driver at it's 12V-35V input pin but it's not working. If I'm connecting to 7.2V supply it's working. Is there any way to connect 5v supply? I want a constant 5v at output pins for motors.
Note: Since all vendors (checked Mouser, Octopart, and Sparkfun) link to the L298 datasheet when listing the L298N I will assume they are reasonably equivalent.
I will assume that the "12V-35V input pin" is the V_S pin, despite that label. There are only two supply pins on the L298 with the following electrical characteristics:
- V_S, Supply Voltage, pin 4, Operative Condition V_IH + 2.546V (max.: 46V)
- V_SS, Logic Supply Voltage, pin 9, typical 5V (min.: 4.5V, max.: 7V)
- V_IH, Input High Voltage, ranging from 2.3V to V_SS
Which would explain that the circuit works at 7.2V under the assumption that the logic inputs (enable A and B as well as inputs 1 through 4) are at close to 5V high levels. And here's the trick that might make it work: as noted V_S (the supply voltage) needs to be at a level of V_IH + 2.546V while V_IH could be as low as 2.3V and 2.3V + 2.546V < 5V. So driving the L298's logic inputs with a lower voltage for logic 1, i.e. closer to 2.3V high levels, could help.
Why is this? (source):
[..] The actual restriction is that the motor supply be somewhat greater than the logic "1" input, but that need not match the logic supply. [..]
A warning though:
- this circuit is now operating at the fringes, one might call it shady at best, intolerable at worst
- saturation voltage is related to output current and other parameters, e.g. temperature, so this might work now under certain conditions and fails horribly another day
Therefore better bets are:
- use a higher supply voltage
- ditch the L298 and its high voltage drop Darlingtons and use a MOSFET H-bridge motor driver, such as the TB6612FNG, see also
- ditch the L298 and use single bipolar transistors, depending on the output current
Other things to check:
Make sure V_SS is connected to the logic supply voltage (see AnT's comment). Make sure GND of the Arduino's power supply is connected to the L298's GND.