Microchip TC7920K6-G: Datasheet, Pinout, and Application Circuit Design
The Microchip TC7920K6-G is a highly integrated, 6-channel, low-side predriver IC designed specifically for controlling three-phase brushless DC (BLDC) motors. It serves as a crucial interface between a low-power microcontroller (MCU) and the high-power MOSFETs in the inverter bridge, simplifying motor control system design and enhancing reliability.
This article provides a detailed overview of the TC7920K6-G, covering its key specifications from the datasheet, pinout configuration, and a fundamental application circuit design.
Datasheet Overview and Key Features
The TC7920K6-G datasheet outlines a component built for robust performance. Its primary role is to amplify the PWM control signals from an MCU to drive the gates of N-channel power MOSFETs efficiently.
Key features extracted from the datasheet include:
6-Channel Low-Side Driver: Contains six independent drivers, perfect for the three half-bridges in a standard BLDC motor inverter.
Wide Operating Voltage Range: The driver section operates from 10V to 20V (VDD), suitable for various bus voltages, while the logic interface operates at a MCU-compatible 5V (VCC).
Built-In Charge Pump: This feature generates the necessary voltage above VDD to fully enhance the N-channel MOSFETs, ensuring low RDS(ON) and minimal heat generation. This eliminates the need for an external bootstrap circuit typically required for high-side drivers.
Integrated Error Protection: The IC includes Under-Voltage Lockout (UVLO) protection for both VDD and VCC. If the supply voltage drops below a safe threshold, the outputs are disabled, preventing MOSFETs from operating in a linear region, which could cause catastrophic failure.
High Output Current Capability: With peak output current and sink capabilities, the driver can quickly charge and discharge the large gate capacitances of power MOSFETs, minimizing switching losses and improving overall efficiency.
Pinout Configuration
The TC7920K6-G is available in a 20-pin SSOP package. Understanding its pinout is critical for PCB layout.
The key pins are categorized as follows:
Power Supply Pins (VCC, VDD, CP, GND): `VCC` (Pin 20) powers the internal logic (5V). `VDD` (Pins 1, 19) is the main driver supply voltage (10-20V). `CP` (Pin 2) is the charge pump capacitor connection. `GND` (Pins 10, 11) is the common ground.
Logic Input Pins (IN1~IN6): These six pins (Pins 3, 4, 5, 6, 7, 18) receive the low-voltage PWM control signals from the MCU.
Driver Output Pins (OUT1~OUT6): These six pins (Pins 12, 13, 14, 15, 16, 17) provide the high-current gate drive signals to the low-side MOSFETs.
Fault Output Pin (FO): This open-drain output (Pin 9) goes low to signal a fault condition (e.g., UVLO) to the MCU, allowing for immediate protective shutdown.
Application Circuit Design
A typical application circuit for driving a three-phase BLDC motor is shown in the block diagram below. The design focuses on the interaction between the MCU, the TC7920K6-G, and the power stage.
1. Power Supply Decoupling: Place a 100nF ceramic capacitor close to the `VCC` pin and a 1µF to 10µF ceramic capacitor close to the `VDD` pins to filter high-frequency noise. A larger electrolytic capacitor (e.g., 47µF) may be needed on the VDD line depending on the total gate charge of the MOSFETs.
2. Charge Pump Circuit: Connect a 100nF ceramic capacitor between the `CP` pin and `GND` as specified in the datasheet. This capacitor is essential for the internal charge pump to generate the gate drive voltage.
3. Microcontroller Interface: The six `INx` pins are connected directly to the PWM output pins of the MCU. A series resistor (e.g., 100Ω) can be added to each line to dampen any ringing and limit current, though it is often optional.
4. Gate Driving Outputs: Each `OUTx` pin is connected to the gate of a low-side N-channel MOSFET. It is critically important to use a gate resistor (e.g., 10Ω to 100Ω) in series with each output. This resistor controls the rise/fall time of the gate signal, reducing voltage overshoot and electromagnetic interference (EMI). A reverse-biased diode across this resistor can be used to enable faster turn-off if needed.
5. Fault Monitoring: The `FO` pin should be connected to a interrupt-capable input pin on the MCU via a pull-up resistor (e.g., 10kΩ) to `VCC`. This allows the system to react instantly to fault conditions.
6. Power Stage (Inverter Bridge): The TC7920K6-G drives the low-side MOSFETs. The high-side MOSFETs would require a separate high-side driver solution (like a bootstrap IC) or can be replaced by P-channel MOSFETs, though the latter is less common due to higher cost and RDS(ON).
---
ICGOODFIND Summary: The Microchip TC7920K6-G is a robust and highly reliable solution for low-side driving in three-phase motor control applications. Its integrated charge pump and protection features significantly reduce external component count and design complexity, making it an excellent choice for developers seeking to create efficient and safe BLDC motor drives for appliances, fans, pumps, and other industrial products.
Keywords: Brushless DC (BLDC) Motor Driver, Gate Driver IC, Low-Side Driver, Charge Pump, Under-Voltage Lockout (UVLO)
