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L298 problem

I'm making a robot and I'm using an L298 to drive 2 DC hobby motors (specifically, the tamiya twin gearbox). For some reason, the L298 give out 3.4V on its outputs when applying logic low to the corresponding input. Does anyone know why this is? I am going by the example schematic in the datasheet, using 5V for logic power supply and 9V for motor power supply.

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You can expect a 1.8 to 3V drop from the input voltage of the L298 to the motor output. Actually, it will be even higher at high current draw.

From what you describe and picture, I see a couple of possible issues.

  1. You are using a standard alkaline 9V, which can only deliver a limited current.
  2. The stock motors in the Tamiya twin gearbox only like about 3V.

So you are using to high a voltage supply, with not enough current. You may have gotten your motor to turn by directly connecting the battery, but I'm not sure it would turn under load.

Now, as to why your OUT2 of the L298 is at 3.4V, I only have a guess. Perhaps the internal resistance of the 9V battery is causing a voltage drop internal to the battery.

Try supplying the L298 with 4 AA alkaline batteries, giving 6V and better current capacity. See if that helps.

by disconnecting the motor and checking the voltages that come out on the output pins. While I agree that a 9v battery is not meant for driving motors, I understand that you are trying to figure out why a logic 0 is providing 3.4v at that output.

Are all of your grounds tied together? I could see it being possible that your "ground" is floating if your grounds are separated.

Hello, I had the same problem. The pins number 1 and 15 have very misleading labels: Current Sensing A and Current Sensing B. When you look into the datasheet, you can see this pins must be grounded, even if you don't control the current.