TB6612FNG Motor Driver

What it is

The TB6612FNG is a dual H-bridge motor driver that does the same job as an L298N—standing between a microcontroller’s logic pins and motors that want far more current—but builds its output stage from MOSFETs instead of bipolar transistors. That one change is the whole story: a MOSFET switch drops a few tenths of a volt where the L298N’s stage drops around two.

On a 6 V battery driving 6 V motors, that difference is most of your speed. It is also most of your heat: the L298N wants a heatsink at sustained current, while a TB6612FNG carrier the size of a postage stamp runs merely warm.

How you control it

Each motor takes three signals, plus one shared pin for the chip:

• Two direction pins (AIN1/AIN2 for motor A, BIN1/BIN2 for motor B) select forward, reverse, brake, or coast.
• One PWM pin (PWMA or PWMB) sets speed. Unlike the L298N, where PWM rides on an enable pin, the TB6612FNG has a dedicated PWM input per channel that accepts up to 100 kHz—high enough to switch above the audible range so your robot stops whining.
• One STBY pin, shared. Hold it LOW and both bridges are dead regardless of everything else.

That STBY pin is worth repeating, because it costs beginners an evening: a correctly wired TB6612FNG with STBY left floating or LOW does absolutely nothing, silently, with no error to read.

When to use it

Reach for the TB6612FNG when your motors are small and your battery is precious—which describes nearly every line follower and line maze robot. Small robots run at 6–7.4 V, exactly the range where the L298N’s 2 V tax hurts most, and they run on a battery you would rather not waste as heat.

Stay with the L298N when your motor supply exceeds 13.5 V, which the TB6612FNG cannot accept, or when you need more than about 1.2 A continuous per channel.

Wiring and gotchas

• Drive STBY HIGH. The first thing your setup() should do after pinMode.
• Two supplies, one ground. Motor battery to VM, Arduino 5 V to VCC, and all grounds tied together—Arduino, driver, sensor array, and battery negative. A missing common ground gives control signals no reference, and the failure is silent.
• Respect 13.5 V. There is no on-board regulator and no headroom above the maximum motor supply. A 3S lithium pack at 12.6 V nominal will exceed it when freshly charged.
• A motor spinning the wrong way is a two-second fix. Swap that motor’s two output wires, or invert its direction logic in firmware. Do this before you tune anything else, or you will chase a control bug that is really a wiring one.

Pinout

Two rows on the common SparkFun-style carrier: logic on one side, power and motors on the other.

The truth table

The top row is the one that costs people an evening. A perfectly wired board with STBY floating does absolutely nothing, and floating is what an un-driven pin does. Drive it HIGH in setup(), on the first line after pinMode.

Wiring it to an Arduino

Minimal working code

const int STBY = 12;
const int PWMA = 9, AIN1 = 8, AIN2 = 7;
const int PWMB = 3, BIN1 = 5, BIN2 = 4;

void setup() {
  for (int p : {STBY, PWMA, AIN1, AIN2, PWMB, BIN1, BIN2}) pinMode(p, OUTPUT);
  digitalWrite(STBY, HIGH);          // without this, nothing happens at all
}

// speed: -255..255
void driveA(int speed) {
  speed = constrain(speed, -255, 255);
  digitalWrite(AIN1, speed > 0);
  digitalWrite(AIN2, speed < 0);
  analogWrite(PWMA, abs(speed));
}

void brakeA() {                       // short brake: both direction pins high
  digitalWrite(AIN1, HIGH);
  digitalWrite(AIN2, HIGH);
}

void loop() {
  driveA(200); delay(1000);
  brakeA();    delay(300);
  driveA(-200); delay(1000);
  brakeA();    delay(300);
}

Getting rid of the whine

This is the TB6612FNG’s quiet superpower and almost nobody uses it. The driver accepts PWM up to 100 kHz, but an Arduino Uno’s analogWrite runs at 490 Hz on most pins and 980 Hz on pins 5 and 6 — squarely in the audible band, which is why a robot sings while it drives.

Human hearing tops out around 20 kHz. Push the PWM above that and the noise disappears entirely. On an Uno, pins 9 and 10 are driven by Timer 1, which you can reprogram:

void setup() {
  // Timer1 (pins 9, 10): phase-correct PWM, no prescaler -> ~31.4 kHz
  TCCR1B = (TCCR1B & 0b11111000) | 0x01;
}

That single line moves the switching frequency to about 31 kHz — inaudible, and still well within the driver’s rating. The cost is that Timer 1 is also what the Servo library uses, so you cannot do both on the same timer.

An L298N cannot follow you up there; its bipolar stage switches too slowly and the losses climb sharply with frequency. This is a real, practical advantage of the MOSFET stage beyond the efficiency numbers.

What 0.5 V instead of 2 V actually buys

The lower your supply, the more the difference matters — which is exactly backwards from where people expect it to matter, and exactly why small robots feel transformed by the swap.

There is a thermal consequence too. At 1 A per channel the L298N dissipates roughly 2 W per channel; the TB6612FNG dissipates around 0.5 W across both. That is the difference between a part needing a heatsink and airflow, and a part you can bury under a chassis plate.

Troubleshooting

Two channels can be paralleled for a single motor — tie AIN1 to BIN1, AIN2 to BIN2, PWMA to PWMB, and the outputs together — for roughly 2.4 A continuous. The datasheet supports it, and it is the standard answer when one motor is just over the limit.

When the TB6612FNG is the wrong choice

It is the right default for small robots, and there are three clear cases where it is not.

Above 13.5 V. There is no headroom and no regulator. A 4S pack is out of the question, and a 3S pack needs checking when freshly charged.

Above ~1.2 A continuous per channel, and paralleling the channels does not get you far enough. An L298N manages 2 A per channel with heatsinking, and a BTS7960 goes to 43 A for genuinely large motors.

When you need current sensing or limiting. The DRV8833 is close to the TB6612FNG in every other respect and adds current limiting, which lets the driver protect itself against a stall rather than relying on your code to notice.