L298N Motor Driver

What it is

The L298N is a dual H-bridge motor driver—the muscle between a microcontroller’s delicate logic pins and a motor that wants far more current than those pins can supply. A microcontroller pin can source only a few tens of milliamps; even a small geared DC motor pulls hundreds. The L298N takes low-power direction and speed signals from the board and switches a separate, higher-current motor supply to match. It drives two motors independently, which is exactly what a two-wheeled robot needs.

It is dated—an efficient MOSFET driver like a TB6612FNG or DRV8833 runs cooler and wastes less voltage—but the L298N is everywhere, cheap, rugged, and the module most robotics kits ship with, so it is worth understanding well.

How an H-bridge works

An H-bridge is four switches arranged around the motor in an “H”. Close the top-left and bottom-right switches and current flows one way—the motor spins forward. Close the opposite pair and current reverses—the motor spins backward. That is the whole trick: an H-bridge lets you reverse a motor without rewiring it.

You control each motor with three signals:

• Two direction pins (IN1/IN2) pick forward, reverse, or brake.
• One enable pin (ENA), fed a PWM signal, sets speed by switching the bridge on and off quickly. Full-on PWM is full speed; 50% duty is roughly half.

Feed the enable pin the output of a control loop and you can hold a target speed or steer a robot smoothly instead of lurching between stop and full-tilt.

When to use it

Reach for an L298N—or any H-bridge—any time a microcontroller must drive a brushed DC motor, which is nearly every wheeled robot. Its 2 A per channel comfortably handles the small yellow gear motors used in line followers and rovers.

Choose a MOSFET-based driver instead when efficiency and battery life matter, when your motors are small (the L298N’s voltage drop wastes a lot on a 6 V motor), or when you want the driver to run cool without a heatsink.

Wiring and gotchas

• Two supplies, one ground. The motor battery feeds the motor supply pin; 5 V logic feeds the logic side. Their grounds must be tied together or the control signals have no reference—a classic silent failure.
• It steals ~2 V. The older BJT output stage drops roughly 2 V before the motor sees anything. Give a 6 V motor about 8 V of supply to run at full speed.
• It gets hot. At sustained current the chip needs its heatsink. If motors weaken during a run, check the temperature.
• Mind the on-board 5 V regulator jumper. Many modules can power the logic side from the motor supply—handy, but only up to ~12 V in. Above that, remove the jumper and supply 5 V separately or you will cook the regulator.

Pinout

The red L298N module everyone means has three terminal blocks and two pin headers.

The two little jumpers on ENA and ENB are the reason so many first attempts have direction control but no speed control: while they are fitted, the channel is permanently enabled and PWM does nothing. Pull them off and wire those pins to PWM-capable outputs.

The third jumper, next to the power block, enables the onboard 5 V regulator.

The truth table

Three signals per motor, and six meaningful combinations. This table is the whole control interface.

Brake and coast are genuinely different, and the difference matters more than people expect. Coasting lets the robot roll on; braking shorts the motor’s own back-EMF through the bridge, which dumps the rotational energy as heat and stops it far more sharply. A line follower that overshoots every junction is often one that coasts when it should brake.

Wiring it to an Arduino

The 5 V regulator jumper, decided properly

Above roughly 12 V the linear regulator has to burn the difference as heat and it will cook. Below about 7 V it cannot maintain 5 V, and the logic browns out as the motors load the pack. Both failures look like random resets.

Minimal working code

const int ENA = 9, IN1 = 8, IN2 = 7;
const int ENB = 3, IN3 = 5, IN4 = 4;

void setup() {
  for (int p : {ENA, IN1, IN2, ENB, IN3, IN4}) pinMode(p, OUTPUT);
}

// speed: -255..255. Negative is reverse, 0 coasts.
void driveA(int speed) {
  digitalWrite(IN1, speed > 0);
  digitalWrite(IN2, speed < 0);
  analogWrite(ENA, abs(constrain(speed, -255, 255)));
}

void brakeA() {
  digitalWrite(IN1, HIGH);
  digitalWrite(IN2, HIGH);
  analogWrite(ENA, 255);
}

void loop() {
  driveA(180); delay(1500);   // forward
  brakeA();    delay(500);    // stop hard
  driveA(-180); delay(1500);  // reverse
  driveA(0);   delay(500);    // coast
}

Note driveA(0) coasts rather than brakes — setting the duty to zero disables the bridge. If you want a hard stop you must ask for one.

The 2 V problem, quantified

The L298N’s output stage is built from bipolar transistors, and each conducting pair drops voltage. The datasheet gives a total saturation drop of roughly 1.8 V at 1 A and up to about 2.7 V at 2 A. That voltage never reaches the motor; it becomes heat in the chip.

The consequences are worth seeing as numbers:

On a 6 V motor running from 6 V, a third of your battery is heating a chip. This is the whole reason the L298N feels weak on small robots — and why a 6 V motor wants roughly 8 V of supply behind this driver.

It is also a thermal problem. At 1 A per channel with both motors running, the chip is dissipating around 4 W. The little heatsink handles that only with airflow, and a current-limited stall will push it into thermal shutdown — which presents as motors that fade out mid-run and recover after a pause.

Troubleshooting

L298N or TB6612FNG?

Choose the TB6612FNG for essentially any small robot: two yellow gearmotors, a line follower, a maze solver. The efficiency difference is not marginal — on a 6 V system it is a third of your battery.

Choose the L298N when the motor supply exceeds 13.5 V, when you need more than about 1.2 A continuously per channel, or when it is simply what came in the kit. It is rugged, tolerant of abuse, and understanding it teaches you the H-bridge properly.

For newer designs also worth knowing: the DRV8833 (similar to the TB6612FNG, with current limiting) and the BTS7960 (43 A, for genuinely large motors).