Introduction to the IRLB8721 MOSFET
The IRLB8721 is an N-Channel 30V Logic Level Power MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) designed for high-efficiency power switching applications. This MOSFET is particularly suitable for use in low-voltage, high-current applications such as DC-DC converters, motor drivers, and power management systems.
Key Features of the IRLB8721
- Logic level gate drive compatibility (4.5V to 20V)
- Low on-state resistance (RDS(on)) for minimal power loss
- Fast switching speeds for high-efficiency operation
- Robust design with high avalanche energy capability
- TO-220AB package for easy mounting and heat dissipation
Understanding MOSFETs
What is a MOSFET?
A MOSFET is a type of transistor that uses an electric field to control the flow of current through a semiconductor channel. MOSFETs have three terminals: the gate, source, and drain. The gate terminal controls the flow of current between the source and drain terminals.
Types of MOSFETs
There are two main types of MOSFETs:
- N-Channel MOSFETs: These MOSFETs conduct current when a positive voltage is applied to the gate terminal relative to the source terminal.
- P-Channel MOSFETs: These MOSFETs conduct current when a negative voltage is applied to the gate terminal relative to the source terminal.
MOSFET Operation
A MOSFET operates in three regions:
- Cut-off Region: When the gate-to-source voltage (VGS) is below the threshold voltage (VTH), the MOSFET is in the cut-off region and does not conduct current.
- Linear Region: When VGS is above VTH, and the drain-to-source voltage (VDS) is less than VGS – VTH, the MOSFET operates in the linear region, and the drain current (ID) is proportional to VDS.
- Saturation Region: When VGS is above VTH, and VDS is greater than VGS – VTH, the MOSFET operates in the saturation region, and ID remains constant regardless of changes in VDS.
IRLB8721 Specifications
Absolute Maximum Ratings
| Parameter | Symbol | Value | Unit |
|---|---|---|---|
| Drain-to-Source Voltage | VDS | 30 | V |
| Gate-to-Source Voltage | VGS | ±20 | V |
| Continuous Drain Current (25°C) | ID | 62 | A |
| Pulsed Drain Current (25°C) | IDM | 200 | A |
| Total Power Dissipation (25°C) | PD | 83 | W |
| Operating Junction Temperature | TJ | -55 to 175 | °C |
| Storage Temperature | TSTG | -55 to 175 | °C |
Electrical Characteristics (TJ = 25°C unless otherwise noted)
| Parameter | Symbol | Min | Typ | Max | Unit |
|---|---|---|---|---|---|
| Gate Threshold Voltage (VDS = VGS, ID = 250µA) | VGS(th) | 1.0 | 1.5 | 2.5 | V |
| Static Drain-to-Source On-Resistance (VGS = 10V, ID = 20A) | RDS(on) | – | 5.5 | 6.5 | mΩ |
| Gate Charge (VDS = 15V, ID = 20A, VGS = 10V) | Qg | – | 48 | – | nC |
| Input Capacitance (VDS = 15V, VGS = 0V, f = 1MHz) | Ciss | – | 2300 | – | pF |
| Output Capacitance (VDS = 15V, VGS = 0V, f = 1MHz) | Coss | – | 450 | – | pF |
| Reverse Transfer Capacitance (VDS = 15V, VGS = 0V, f = 1MHz) | Crss | – | 130 | – | pF |
| Turn-On Delay Time (VDD = 15V, ID = 20A, VGS = 10V) | td(on) | – | 10 | – | ns |
| Rise Time (VDD = 15V, ID = 20A, VGS = 10V) | tr | – | 25 | – | ns |
| Turn-Off Delay Time (VDD = 15V, ID = 20A, VGS = 10V) | td(off) | – | 24 | – | ns |
| Fall Time (VDD = 15V, ID = 20A, VGS = 10V) | tf | – | 15 | – | ns |
Applications of the IRLB8721
DC-DC Converters
The IRLB8721 is well-suited for use in DC-DC converters due to its low on-state resistance and fast switching speeds. These properties help minimize power losses and improve the overall efficiency of the converter.
Example: Synchronous Buck Converter
In a synchronous buck converter, the IRLB8721 can be used as the low-side MOSFET, while a complementary P-Channel MOSFET is used as the high-side switch. The IRLB8721’s logic level gate drive compatibility simplifies the gate driver design, as it can be directly driven by the PWM controller’s output.
Motor Drivers
The IRLB8721’s high current capability and robust design make it an excellent choice for motor driver applications. Its low on-state resistance helps minimize power dissipation, while its fast switching speeds enable precise control of the motor’s speed and torque.
Example: H-Bridge Motor Driver
In an H-Bridge motor driver, four IRLB8721 MOSFETs can be used to control the direction and speed of a DC motor. By selectively turning on the appropriate pair of MOSFETs, the motor can be driven in either direction, while PWM control of the MOSFETs allows for smooth speed regulation.
Power Management Systems
The IRLB8721’s high efficiency and compact TO-220AB package make it suitable for use in various power management systems, such as voltage regulators, battery management systems, and power distribution networks.
Example: Low-Dropout (LDO) Voltage Regulator
In an LDO voltage regulator, the IRLB8721 can be used as the pass element, controlling the flow of current from the input to the output. Its low on-state resistance helps minimize the voltage drop across the MOSFET, allowing for a lower minimum input-to-output voltage difference and improved efficiency.
Designing with the IRLB8721
Gate Driver Considerations
When designing with the IRLB8721, it is essential to choose an appropriate gate driver that can provide the necessary drive current and voltage levels. The gate driver should be able to supply a peak current sufficient to charge and discharge the MOSFET’s input capacitance within the desired switching time.
Example: Gate Driver Selection
For a switching frequency of 100kHz and a desired rise time of 25ns, the required peak gate drive current can be calculated as:
I_peak = Qg / tr = 48nC / 25ns = 1.92A
A gate driver with a peak output current of at least 2A should be selected to ensure proper operation of the IRLB8721.
PCB Layout Considerations
Proper PCB layout is crucial for optimal performance of the IRLB8721. The following guidelines should be followed to minimize parasitic inductances and resistances, which can lead to voltage spikes, ringing, and increased power losses:
- Keep the gate drive loop as small as possible to minimize gate ringing and overshoot.
- Place the input capacitor close to the MOSFET to minimize the power loop inductance.
- Use a wide, short trace for the MOSFET’s source connection to minimize the source inductance.
- Provide an adequate heatsink or copper area for thermal dissipation.
Thermal Management
The IRLB8721’s power dissipation and thermal management must be considered to ensure reliable operation. The MOSFET’s junction temperature should be kept within the specified limits to prevent damage and maintain performance.
Example: Heatsink Selection
Given a maximum ambient temperature of 50°C, a maximum junction temperature of 175°C, and a power dissipation of 20W, the required thermal resistance from junction to ambient can be calculated as:
R_ja = (TJ_max – TA_max) / PD = (175°C – 50°C) / 20W = 6.25°C/W
A heatsink with a thermal resistance of less than 6.25°C/W should be selected to ensure the IRLB8721 operates within its thermal limits.
Frequently Asked Questions (FAQ)
1. What is the difference between a logic level MOSFET and a standard MOSFET?
A logic level MOSFET, like the IRLB8721, can be fully turned on with a gate voltage of 4.5V or less, making it compatible with logic level signals from microcontrollers and other low-voltage control circuitry. Standard MOSFETs typically require gate voltages of 10V or more to fully turn on, which may necessitate the use of additional gate drive circuitry.
2. Can the IRLB8721 be used in parallel to increase current capacity?
Yes, multiple IRLB8721 MOSFETs can be connected in parallel to increase the current handling capacity of the system. However, it is essential to ensure that the MOSFETs are properly matched and have equal gate drive characteristics to prevent current imbalances and ensure optimal performance.
3. What is the purpose of the MOSFET’s intrinsic diode?
The IRLB8721, like all MOSFETs, has an intrinsic body diode that conducts current from the source to the drain when the MOSFET is turned off. This diode is essential in applications where inductive loads are present, as it provides a path for the inductive current to flow during the MOSFET’s off-state, preventing voltage spikes and potential damage to the device.
4. How does the IRLB8721’s on-state resistance vary with temperature?
The IRLB8721’s on-state resistance (RDS(on)) increases with increasing junction temperature. This is an important consideration in power dissipation calculations and thermal management design, as higher on-state resistance leads to increased power losses and heat generation.
5. What is the purpose of the MOSFET’s avalanche energy rating?
The avalanche energy rating specifies the maximum energy the MOSFET can dissipate during an avalanche breakdown event without suffering damage. Avalanche breakdown occurs when the drain-to-source voltage exceeds the device’s breakdown voltage, leading to a rapid increase in current. The IRLB8721’s robust design and high avalanche energy rating make it more resilient to such events, enhancing the system’s overall reliability.
Conclusion
The IRLB8721 N-Channel 30V Logic Level Power MOSFET is a versatile and efficient choice for a wide range of power switching applications. Its low on-state resistance, fast switching speeds, and logic level gate drive compatibility make it particularly well-suited for use in DC-DC converters, motor drivers, and power management systems.
By understanding the IRLB8721’s specifications, application considerations, and design guidelines, engineers can effectively integrate this MOSFET into their designs to achieve optimal performance, efficiency, and reliability.
As with any power electronic component, proper selection, design, and thermal management are essential to ensure the IRLB8721 operates within its specified limits and meets the application’s requirements. By following best practices and considering the device’s characteristics, designers can harness the full potential of this logic level power MOSFET in their projects.
