When we talk about switching power MOSFETs quickly and efficiently, one of the big challenges engineers face is how to drive those gates. MOSFETs have significant input capacitance, and pushing or pulling that gate charge at high speeds requires both current capability and precise timing. That’s where dedicated MOSFET driver ICs come into play. Among the well-known options are the TC4420 and TC4429, high-speed MOSFET drivers designed by Microchip (originally from TelCom Semiconductor). These chips have been around for a while, but they’re still widely used in switching power supplies, motor control, and digital power circuits.
Let’s break this down step by step in a casual, notebook-style way, but still with all the necessary depth.
1. What They Are
The TC4420 and TC4429 are basically high-current, high-speed drivers meant to control MOSFETs (or IGBTs, sometimes). They sit between the logic-level control signals (like from a microcontroller, DSP, or PWM generator) and the power MOSFET itself. Since MOSFETs often require amps of current just to charge and discharge their gates fast enough, you can’t always rely on a microcontroller pin directly—its drive strength is way too weak.
•TC4420 is non-inverting: meaning, if you put in a HIGH logic signal, you get a HIGH output at the driver pin.
•TC4429 is inverting: meaning, a HIGH input results in a LOW output, and vice versa.
This gives designers flexibility depending on the system requirements.
2. Key Features
Some of the standout specifications:
•High Peak Output Current: Both can source and sink around 6A peak. That’s a lot compared to most logic circuits.
•Wide Supply Voltage Range: They can operate anywhere from 4.5V up to 18V. This makes them handy for both logic-level MOSFETs (say, at 5V) and higher-voltage gate drives (like 10V–12V).
•Fast Switching: Typical rise and fall times are in the 25ns–30ns range when driving capacitive loads.
•Low Output Resistance: About 1.5Ω sourcing and sinking. That ensures good current delivery.
•Latch-Up Protected: They’re designed so that output won’t latch up when inputs go below ground.
•Input TTL/CMOS Compatibility: Inputs can be driven directly by microcontrollers or DSP outputs without needing extra interfacing.
•Robustness: They’re internally protected against shoot-through and can handle heavy gate-drive demands.
So in simple terms: they’re tough, fast, and versatile.
3. Internal Architecture (Simplified)
Inside each chip, the structure is straightforward but optimized for speed:
1.Input Buffer: Takes in the TTL/CMOS logic signal and conditions it.
2.Level Shifter: Ensures the logic is translated to the driver’s supply level.
3.Totem-Pole Output Stage: This is the big one. A pair of complementary MOSFETs (one pulling high, one pulling low) can quickly push or pull current into the load (the MOSFET gate).
4.Inverting/Non-Inverting Path: That’s the only difference between the 4420 and 4429.
This architecture ensures minimal propagation delay (about 55ns typical). That’s small enough for high-frequency switching applications.
4. Applications
These drivers are very popular in various switching environments. Let’s go through some:
a) Switch-Mode Power Supplies (SMPS)
In buck, boost, or flyback converters, MOSFETs need to be switched at high frequencies (tens or hundreds of kHz). The TC4420/4429 can quickly charge/discharge the MOSFET gates, reducing switching losses and improving efficiency.
b) Motor Control
In BLDC and stepper motor drivers, MOSFETs are used in H-bridges or half-bridges. Proper driver chips are required for fast transitions, otherwise motors will lose torque or efficiency.
c) DC-DC Converters
Portable devices and industrial converters need reliable gate drivers.
d) Class-D Amplifiers
Audio power amplifiers in Class-D rely on fast MOSFET switching. These drivers help push gates at MHz speeds.
e) General High-Speed Switching Circuits
Any circuit needing clean, fast transitions with MOSFETs—such as pulse circuits, digital power distribution, or even experimental RF setups.
5. Practical Advantages
Here’s why designers like the TC4420/4429:
•Versatility: The wide supply range lets you drive MOSFETs in both logic-level (5V) and “standard” (10–12V) gate voltages.
•Inverting vs Non-Inverting Options: You don’t need an extra inverter if your logic is reversed—just pick the right part.
•High Drive Strength: Driving big MOSFETs with high gate charge is no problem.
•Robust Build: Tolerates noisy environments, undershoot, and ringing better than weaker drivers.
•Ease of Use: Drop-in DIP or SOIC packages, simple two-pin input/output interface.
6. Limitations and Considerations
Nothing’s perfect. Some things to keep in mind:
•Power Dissipation: Since they can sink/source lots of current, the drivers themselves heat up when switching very fast into large gate capacitances. You need to consider thermal limits.
•Propagation Delay: At ~55ns, they’re fast enough for most applications, but not the absolute fastest on the market today.
•No Integrated Level Shifting for High-Side: These are low-side drivers only. If you need to drive a high-side MOSFET in a half-bridge, you’ll need a bootstrapped driver like the IR2110 or similar.
•Limited Input Protection: Inputs are TTL/CMOS, so they shouldn’t be left floating or driven above Vdd.
Still, for many mid-frequency switching jobs, these drivers are more than adequate.
7. Example Circuit
Imagine you’re designing a buck converter with a switching MOSFET. Your microcontroller gives a PWM signal at 100kHz. That PWM alone cannot directly drive the MOSFET gate, because the MOSFET might have, say, 50nC gate charge, and your MCU pin can only source a few mA.
Solution: put a TC4420 between them. The MCU PWM drives the TC4420 input, and the TC4420 then pushes/sinks up to 6A into the MOSFET gate. The MOSFET turns on and off very quickly, reducing switching losses, which improves efficiency.
If for some reason your system requires the PWM to be inverted, you’d use a TC4429 instead. That way, you avoid extra inverter circuitry.
8. Electrical Characteristics Snapshot
•Supply Voltage (Vdd): 4.5V–18V
•Output Current (peak): ±6A
•Input Threshold: ~1.4V (TTL compatible)
•Rise Time/Fall Time: ~25ns–30ns (typical with 1000pF load)
•Propagation Delay: ~55ns
•Output Resistance: ~1.5Ω sourcing/sinking
These numbers show why they’re called “high-speed drivers.”
9. Comparison with Other Drivers
•Compared to TC4426/27/28 family: The 4420/4429 have higher output current (6A vs ~1.5A).
•Compared to IR2110 (high/low-side driver): IR2110 is better for half-bridges, but TC4420/29 is simpler and cheaper for single low-side MOSFET drive.
•Compared to modern ultra-fast gate drivers (like GaN FET drivers): The TC4420/29 are slower, but still reliable workhorses.
So, they sit in the sweet spot: strong, simple, reliable.
10. Real-World Notes
•Decoupling: Always put a ceramic capacitor (like 0.1µF + 10µF) close to the Vdd pin. These drivers pull big transient currents.
•PCB Layout: Keep traces to the MOSFET gate short and wide to minimize inductance and ringing.
•Grounding: Star ground is recommended to prevent noise issues.
•Temperature: Junction temperature should be monitored when driving large loads continuously.
Engineers often underestimate how much gate drive losses heat the driver IC. In high-frequency designs, that’s important.
Conclusion
The TC4420 and TC4429 are classic, rugged, and powerful MOSFET drivers. They deliver high peak currents (6A), fast rise/fall times (~25ns), and can handle a wide range of supply voltages (4.5V–18V). The difference between the two is simply inversion: TC4420 is non-inverting, while TC4429 is inverting.
They shine in applications like switch-mode power supplies, motor drives, Class-D amplifiers, and general high-speed switching. While they don’t have advanced features like high-side drive or ultra-low propagation delays of modern GaN drivers, their balance of speed, drive strength, and simplicity makes them reliable building blocks in power electronics.
In short: if you need a straightforward, heavy-duty MOSFET driver that just works, the TC4420/29 is still a go-to choice for many engineers.
